Part 2 — Core

What every Eurorack product shares, whoever makes it. Core binds every product and is never claimed; a product may add the optional interfaces of Part 3. A Core requirement applies to what a product has: the bus rules bind a product with a power header, and a product without one owes none of them, but for BUS-011, which binds every module (6.4).

Mechanical (chapter 5). What makes a module fit a row and a row fit a rack: the HP and the rack unit (5.1), the front panel and the boards behind it (5.2), the rails, inserts, and mounting screws (5.3), and the enclosure (5.4). The requirements restate the Doepfer A-100 conventions, fix the few figures they leave open, and take the Intellijel 1U format for 1U rows.

Power (chapter 6). Two power interfaces, each with its own connectors, distribution, and limits (6.1); the bus is Core, and the 12 V DC rail an optional interface (Part 3):

• PWR-BUS, the Eurorack bus: ±12 V and optional +5 V from a supply, through bus boards and ribbons, to a module's power header (6.4 to 6.6).
• PWR-DC12 (8.1): nominal 12 V DC from an external adapter or a supply into a product's DC entry. It serves a product that draws more than one power header carries, and a product that runs on a desk, or in a case with no bus, from a wall adapter. Each product filters or regulates its DC rail, so the rail's noise does not reach a signal.

What both share is in 6.1 to 6.3: the currents a product publishes, a source's protection and ripple, and the one 0 V a row's signals are measured from.

Patch signals (chapter 7). What travels on a port, and what every patch jack owes whatever it carries: the port list, patch safety, and the jacks inside the case (7.1); the seven signal classes, AUDIO, CV, VIDEO, PITCH, GATE, TRIG, and CLOCK, with their ranges (7.2); and VIDEO's interface, paths, and bandwidth (7.3).

Contents

• 5.1 Rack dimensions: The 19-inch frame a row sits in
• 5.2 Modules: A module, its panel, or its boards
• 5.3 Rails, inserts, and mounting screws: What makes a panel fit a row
• 5.4 Enclosures: The case a module mounts in
• 6.1 Power architecture: The power interfaces, sources, distribution, entries, and the rules for every power interface
• 6.2 Power supplies: Protection, published ripple, the ripple limit of each power interface
• 6.3 Grounding and 0 V: The 0 V reference, protective earth, and joining cases
• 6.4 The bus: PWR-BUS: rails, header, pinout, marking, keying, and a module on the bus
• 6.5 Bus boards: Capacity, links, ribbons
• 6.6 Bus CV and gate: The 16-pin CV and gate nets
• 7.1 Signals: The port list, patch safety, and the jacks inside the case
• 7.2 Signal classes: The seven signal classes, AUDIO, CV, VIDEO, PITCH, GATE, TRIG, and CLOCK, and their ranges
• 7.3 Video signals: VIDEO on patch jacks: levels, impedances, path kinds, and bandwidth

5.1 Rack dimensions

One HP shall be 5.08 mm (RACK-001) and one rack unit shall be 44.45 mm (RACK-002), quoted from IEC 60297-3-101:2004. Both bind modules and enclosures.

A rack-mount frame, one that fastens into a 19-inch rack, shall meet IEC 60297-3-101:2004 and IEC 60297-3-100:2008 for the flange width, the flange mounting-hole positions and slot, the 3U height H1, and the 84 HP row width (RACK-003). A desktop or portable case needs no flanges; its rows keep the same HP, rack unit, and mounting-hole span (PANEL-009).

The figures RACK-003 applies:

IEC 60297-3-100 applies H1, H2, and H3 to front panels, chassis, and subracks alike (its clause 5.1). Its detail A draws the slot as an oval open at the outer edge, 6.8 mm high (+0.5 / 0) and 14.7 mm deep (±1.2), and also permits a second hole type; the figure draws the open oval.

A front panel sits within H1, between the rails. The IEC publications do not set rail depth; 5.3 gives the recommended section.

The figures are in data/standards.json. The panel and flange figures (482.6 mm, H1, H2, H3, detail A, 1U, 84 × 5.08 mm) are read from the publications' own pages in the IEC's public preview: IEC 60297-3-100:2008 clause 5, Figure 2, and Table 1, and IEC 60297-3-101:2004 Figures 3 and 5 (bibliography). The rack mounting grid (465.1 mm centers, 12.7 mm and 31.75 mm steps) is in IEC 60297-3-100:2008 clause 6, beyond the preview, and is transcribed from the Schroff standards summary; where the two differ, the publication governs. The IEC publications are not stored in this repository.

5.2 Modules

A module fills HP in a row: a front panel, the boards behind it, and the parts on them. It screws to the rails of an enclosure and, unless it is passive, takes power at a power entry (6.1), for most modules its power header, cabled to the row's bus board.

A module shall be 1U or 3U high (PANEL-001); the panel height, the mounting holes, and the board clearance follow from that choice. Its width is any positive whole number of HP (PANEL-002). A module shall publish its width in HP and how far it extends behind the panel's back face (PANEL-003), so that a buyer can check it against the width and depth a row publishes (ENC-001).

Fitting a module into a row, current check first, is in Assembling a system.

Tolerances

A dimension of clauses 5.1 to 5.3 shall hold within the tolerance the register states for its requirement, and a dimension with no tolerance stated is a limit (PANEL-013). The tolerances are in data/requirements.json:

5.2.1 Front panels

A front panel is the plate on the front of a module, or a blank panel that fills unused width in a row. It screws to the rails through a rail insert.

A front panel shall be no more than 2.0 mm thick (PANEL-004). EIS recommends 5052 aluminum or FR-4 circuit board, 1.6 mm to 2.0 mm thick. FR-4 is less stiff, so an FR-4 panel needs extra mounting holes at a narrower width than aluminum (Extra mounting holes).

A front panel thinner than 1.6 mm shall ship with M3 mounting screws with a head at most 7.0 mm across, whose length fits the window of 5.3 for its own thickness on a rail of the section 5.3 recommends (PANEL-014). The enclosure's screws are sized for panels of 1.6 mm to 2.0 mm and can bottom out through a thinner one.

A patch jack shall be a 3.5 mm mono (TS) socket (PANEL-005). 7.1 recommends insulating jacks from the panel; the panel and 0 V says how.

A blank panel plays the panel role of 4.1 and meets the same height, width, thickness, and hole requirements as a module's panel.

The panel and 0 V

A panel makes two choices, and they are independent. A module shall publish both: whether its front panel is connected to its 0 V, and whether the panel is bonded to the rails (PANEL-015).

EIS recommends the first row: a panel insulated from 0 V, bonded to the rails if it is metal and the maker wants a shield, floating otherwise. Insulated means that nothing at 0 V touches the panel: not a jack's sleeve, a pot's bushing, a switch's frame, or an encoder's body.

Insulated jacks on an FR4 panel

The usual 3.5 mm jack has a metal threaded bushing, about 6 mm across, a hex nut of 8 mm across the flats (9.2 mm across the corners) and a washer of about 9.5 mm. On an FR4 panel the board itself is the insulator, and the jack is insulated by keeping the panel's copper away from everything the jack touches:

• the hole is unplated (NPTH), to the jack's drawing, about 6.1 mm to 6.4 mm for a 6 mm bushing;
• no copper on any layer within a circle at least 1 mm beyond the nut's corners and the washer: Ø12 mm for the jack above, centered on the hole, so that the hole's bore, the nut, and the washer meet no copper;
• solder mask may run over the panel's copper up to the keep-out and across it; it is cosmetic, not the insulation: 15 µm to 30 µm of mask under a nut turned to torque may or may not be cut through, which is also why GND-004 refuses it as a bond surface;
• the same keep-out on the back face, where the jack's body sits; the usual jacks have plastic bodies, and a metal-cased jack or a pot's bushing needs the keep-out to cover whatever it touches.

The jack's sleeve is then at the module's 0 V on the board behind the panel and nowhere else, and the panel's copper is free to be bonded to the rails through finished lands at the mounting holes, or left floating.

Insulated jacks on a metal panel

A metal bushing through a bare metal panel is a connection, and through an anodized one it may or may not be: anodize in a hole's bore is thin, and a bushing turned into it cuts through or does not. To insulate a jack on a metal panel, use a jack whose bushing is plastic, or an insulating shoulder washer in an oversized hole with a flat insulating washer under the nut. Pots, switches, and encoders with metal bushings take the same treatment. Otherwise the panel is published as connected to 0 V, and EIS recommends that the connection be made a bond, bare metal under at least one bushing's nut or washer, rather than whatever a bushing scratches through anodize.

Height

A 3U front panel shall be 128.5 mm high (PANEL-006): 4.85 mm under three rack units (133.35 mm), so it fits within the 132.55 ± 0.4 mm 3U height H1 of 5.1. The 4.85 mm is clearance, not a rail lip; where a rail has a lip, EIS recommends at most 1.5 mm (5.3).

A 1U front panel shall be 39.65 mm high (PANEL-007), the Intellijel 1U format, 4.80 mm under one rack unit. EIS defines no other panel height.

Mounting holes shall be 3.0 mm in from the top and bottom panel edges (PANEL-008). A panel that is to be chassis is bonded to the rails only by what is under its screw heads (6.3): EIS recommends a bare 7 mm disc at each hole on a coated panel, or a finished copper land on an FR4 one. The hole span is then the panel height less 6.0 mm, and it shall be 122.5 mm at 3U and 33.65 mm at 1U, the same on the panel and between the inserts of a row's two rails (PANEL-009).

Width

The nominal width of an N HP panel is N × 5.08 mm, where N is any positive whole number. An N HP panel shall be no wider than its nominal width (PANEL-002). EIS recommends making it 0.3 mm narrower, so that neighboring panels do not bind:

panel width = N × 5.08 − 0.3 mm

The board behind the panel is 0.6 mm under the nominal width (5.2.2). A rail gives at least the nominal width of its row (RAIL-002), so a row of panels at either width fits it.

Mounting holes

Mounting holes shall be drilled Ø3.2 mm, or slotted 3.2 mm wide and no longer than 5.5 mm along the rail, centered on the hole position (PANEL-010). Either clears the M3 mounting screw; a short slot takes up a rail's position error without letting the panel drop.

Along the rail, each mounting hole shall be a whole number of HP plus 2.54 mm from the panel's nominal left edge (PANEL-011). The nominal edges are N × 5.08 mm apart and centered on the panel, so every hole meets a hole in the rail insert, whatever the panel's width and wherever it sits in the row. The top and bottom rows of holes are the same.

Measured from the panel center:

• an odd-HP panel has its holes a whole number of HP out, an even-HP panel a whole number of HP plus 2.54 mm;
• from 3 HP up, the outer holes are 7.62 mm in from each nominal edge, which puts the one hole of a 3 HP panel on its center;
• a 1 HP panel has one hole, on its center, and a 2 HP panel has its holes at ±2.54 mm.

The two cards below show an 8 HP panel.

Extra mounting holes

EIS sets no hole count; four holes are the usual pattern. A wide panel needs more so that a 10 N push at midspan, about the force of seating a plug, bows it no more than 0.5 mm between screws. On four screws a 3U panel reaches 41 HP in 1.6 mm 5052 and 26 HP in 1.6 mm FR-4, the most flexible recommended sheet; past that, a hole is added on each rail, a middle hole first, until every gap is inside the span. On an even-HP panel the middle hole sits 2.54 mm to one side of the center, on the hole grid.

The numbers are in data/module.json. tools/module.py derives the hole spans and widths and computes the extra-hole patterns; tools/cards_system.py draws the span card.

5.2.2 Boards

The circuit boards behind a front panel. A module has a parallel board, a right-angle board, or both.

Edge clearance

A board shall stay at least 9.25 mm clear of the top and bottom panel edges, and a rail shall cover no more than 9.25 mm of the panel face at each edge (PANEL-012). The rails' inner faces are then at least 110 mm apart at 3U and 21.15 mm at 1U. A 110 mm board is the tallest that fits at 3U; the usual 1U board is 21.10 mm, two rack units shorter.

On a rail whose inner face is 5.075 mm from the hole center, such as Schroff 34560-184, the 3U opening is 112.35 mm and a 110 mm board has 1.175 mm to spare on each side. 5.3 gives the inner-face measurements of catalog rails.

The rest of this clause describes common construction and sets no requirement. The numbers are in data/module.json.

Parallel boards

A parallel board faces the panel. Its front face is usually 10 mm behind the panel's back face, the height of a jack body. Its width is 0.6 mm under the panel's nominal width, twice the panel clearance:

board width = N × 5.08 − 0.6 mm

An 8 HP parallel board is 40.04 mm wide, and 110 mm tall at 3U or 21.10 mm at 1U. 1.6 mm FR-4 is the usual material.

Right-angle boards

A right-angle board stands square to the back of the panel, with no gap. Its left edge meets the panel, and its parts face right. Its height is the board height above. Its depth is the maker's choice, and the module publishes how far it reaches (PANEL-003). Even a 30 mm deep right-angle board reaches past a rail of the recommended section (5.4).

Module depth

EIS recommends that a module extend no more than 50 mm behind the panel's back face, measured to its deepest point. A deeper module still conforms; its published depth (PANEL-003) is checked against the row's (ENC-001). In the eis-reference survey, 94.8 % of 270 modules are within 50 mm and the median is 35 mm.

5.3 Rails, inserts, and mounting screws

A front panel screws to a pair of rails through a threaded rail insert in each. Five things make a module fit any conforming row:

Rails and inserts

The holes in a rail insert shall be 5.08 mm apart (RAIL-001), so that every panel hole meets one. A rail for an N HP row shall give at least N × 5.08 mm of mounting length (RAIL-002).

An insert shall be threaded M3 (RAIL-003) and shall be at least 1.5 mm thick, three thread pitches (RAIL-004).

Mounting screws

A mounting screw shall be M3 (RAIL-005): its thread pitch shall be 0.5 mm (RAIL-006) and its major diameter 3.0 mm (RAIL-007), as ISO 261:1998 gives them. M3 is the thread of the Doepfer A-100 frame, of nearly every Eurorack case on sale, and of the screws modules ship with. A case built on M2.5 IEC subrack hardware, or on #4-40 groove nuts in a Vector T-strut, is not an EIS row, though a module's Ø3.2 mm hole (PANEL-010) clears those screws.

A mounting screw shall engage at least three full threads through a 2.0 mm panel (RAIL-008). Its length L shall fall inside this window, and the throat in front of the insert shall clear the 3.0 mm major diameter (RAIL-009):

2.0 mm + seat + 1.5 mm  ≤  L  ≤  1.6 mm + D

Seat is the depth of the insert's front face behind the rail's mounting face, and D is the depth of the screw cavity behind it (Terms). The upper bound keeps the tip off the cavity floor through a 1.6 mm panel, the thinnest EIS recommends.

The screw head shall be at most 7.0 mm across (RAIL-010). The narrowest catalog rail face reaches 3.7 mm past the hole center (the Vector T-strut, half its 7.391 mm height), so a head of that size bears on the panel and on the rail face of every catalog rail; an ISO 7045 pan head or a 7 mm washer fits.

An enclosure shall publish the mounting-screw length, and shall supply those screws or name them (RAIL-011). A module need not ship with screws unless its panel is thinner than 1.6 mm (PANEL-014).

Recommended practice

Everything else about a rail, an insert, and a screw is construction: the extrusion section and its lip, the groove, the insert width and ends, the screw lengths, the tap drill, the head form, and the finish. EIS recommends the following for a new rail; a rail built another way conforms if it meets the requirements above.

Recommended rail section

Two vendor figures recur in EIS. The Vector T-strut height (drawing 5280006) is the small end of the recommended height below. The inner face of the Schroff 34560-184 section, with the mounting hole on the cavity center, sets the board opening in 5.2.2: 112.35 mm at 3U, 1.175 mm more on each side than a 110 mm board.

A new rail inside these limits takes the 5.0 mm × 2.0 mm M3 strip most Eurorack cases use, and a 6, 8, or 10 mm screw. The limits are the envelope of the two extrusions EIS measured, rounded: the Vector T-strut at the small end, the Schroff L-KD at the large. A rail built another way conforms if it meets 5.3.

A lip is optional; its two limits include its corner radius. The groove admits a rectangular insert 5.0 mm across and 2.0 mm thick; a larger groove is fine if that rectangle enters and stays. The throat in front of the insert clears 3.0 mm (RAIL-009). EIS recommends that a rail maker publish the insert seat, the screw-cavity depth D, and a screw length that fits the window (RAIL-009).

An N HP strip is N × 5.08 + 4.58 mm long with N holes, or is cut from a longer strip; the first-hole and end-margin figures are measured on the Schroff 34561-484 model. A slide nut fits the same 5.0 mm × 2.0 mm section. M3 slide nuts for Eurorack rails are made to the groove; a DIN 562 M3 square nut, 5.5 mm across flats, does not fit it.

The numbers are in data/rail.json, data/insert.json, and data/screw.json; tools/rail.py, tools/insert.py, tools/insert_card.py, and tools/screw.py check them and draw the cards. The catalog rail sections and inserts measured against these limits, and the screw that fits each, are in the eis-reference repository.

5.4 Enclosures

The case a module screws into. An enclosure is made of rows; each row has a pair of rails with an insert in each, and usually a bus board behind the panels.

Rows

An enclosure shall publish, for each row, its width in HP and the depth it keeps clear behind the panel's back face (ENC-001).

A row is 1U or 3U, matching the front panels it holds; a 6U case is two 3U rows. A row's usable width is a whole number of HP. 84 HP fits a 19-inch rack; wider rows, such as 104 HP, are the maker's choice.

Frame

The frame is a 19-inch rack frame, which meets RACK-003 (5.1), or a desktop or portable frame with the same rows and hole span (5.3).

The front rails take the mounting screws of 5.3, whose length the enclosure publishes (RAIL-011). Other rails carry the bus board or stiffen the frame. The enclosure publishes which of its metal parts are bonded to one another and where its metalwork takes a bond to the row's 0 V (GND-005, 6.3): anodized rails and inserts lying in them are not bonded by their fit. Mains inlet, fusing, and the construction of a supply are outside EIS.

Depth

EIS recommends that a row keep at least 50 mm clear behind the panel's back face, the module depth 5.2.2 recommends. A rail of the recommended section (5.3) is 25 mm to 28.5 mm deep, front face to back face. In the case catalog behind the eis-reference survey, 20 of 25 current cases give 50 mm somewhere in the row and 17 give it over the whole row; the shallow part is usually over the supply or the bus board.

Built-in supply and bus board

An enclosure with a built-in supply is also a power supply, and one with a built-in bus board is also a bus board. Each built-in part claims its own role (4.1), and the enclosure's documentation carries what each publishes:

• a built-in supply publishes its rail ratings and its ripple and noise (PWR-002, SUP-001), meets SUP-002 to SUP-007 (6.2), and publishes how its 0 V meets protective earth (GND-003, 6.3);
• a built-in bus board publishes its totals and its per-header limit (PWR-002), which BUS-012 caps at 1.5 A per rail where it has PWR-BUS outlets.

EIS recommends that an enclosure publish, for each row, the dissipation it carries for a 10 °C rise above room temperature; Annex H gives the method.

The informative row budget is a planning table for one row: header count, bus and supply currents, and video sync distribution.

6.1 Power architecture

EIS power comes in two power interfaces. A power interface is a set of rails with its own connectors, its own way of reaching a module, and its own limits:

• PWR-BUS, the bus: +12 V and −12 V, and optionally +5 V, that a power supply feeds through bus boards and power ribbons to each module's power header;
• PWR-DC12: nominal 12 V DC from an external adapter or a supply, which enters a product at a DC entry.

PWR-BUS is Core; PWR-DC12 is an optional interface (8.1). A product takes a power interface at an entry and gives it at outlets, and its claim file lists each (4.2). An interface's rules apply to a product that has an entry or an outlet of it; a passive module, with neither, owes none of them but BUS-011, which binds every module (6.4).

The designators follow one rule: the word after PWR names the interface's topology, and a number its rail voltage. BUS, the Eurorack bus, is defined by its header pinout rather than by one voltage, so it has no number; DCnn is a single nn V DC rail fed from an adapter, the trade's DC jack.

This clause, 6.2 (sources), and 6.3 (0 V) hold what both interfaces share. The bus has 6.4 to 6.6, and PWR-DC12 has 8.1. A maker's own power entry at other rails is outside EIS: the product names it in its claim file as an entry EIS does not cover, and it adds no requirement. Mains voltage, safety certification, and the internal construction of a supply are outside EIS.

Power interfaces

Sources, distribution, and entries

On each interface, a source makes the power: a power supply, for a row or for the one product it is mounted on. Distribution passes it on without converting it. A product takes it at a power entry: a module's power header or its DC entry. A source or a distribution product delivers at outlets: a supply's output terminals, a bus board's headers, and the PWR-DC12 outlets (DC-BAR21 jacks or DC-VH2 headers) of a bus board, a module, or a supply.

One product can sit on both interfaces:

• a power supply that takes PWR-DC12 at a DC entry and delivers the bus is a PWR-DC12 entry and a bus source;
• a dual-source module has a power header and a DC entry;
• a supply mounted on one product is an entry of the interface it takes and a source of the one it makes.

Rules for every power interface

A product shall publish, for each power entry, the maximum current it takes on each rail at the entry's nominal voltage, stating 0 for a rail it does not draw (PWR-001). A power supply, a bus board, and any product with power outlets shall publish the maximum current it delivers on each rail, in total and at each outlet (PWR-002). The person assembling a system budgets a row with these figures (ASM-001).

A product whose power entries are alternatives, each able to power it alone, shall not require more than one of them to be connected at the same time (PWR-003); the installer connects one (ASM-003). Entries that feed different circuits, such as a DC entry for one board and the bus for another, are not alternatives, and the claim file says which the product needs.

A module shall not source current into a rail of any of its power entries (PWR-004). A module with its own +5 V regulator leaves pins 11 and 12 of its power header undriven, and a module with a DC entry does not feed its DC rail onto the bus.

Every power entry's 0 V, and the −V of a DC entry, is the product's one 0 V (GND-001, 6.3).

A row of modules is a large capacitive load on its source; a supply states the capacitance it starts into (6.2), and EIS recommends that a product limit the inrush its own decoupling draws.

Row wiring

Row wiring is the discrete conductors, not a power-interface connector, that join a power supply to its bus boards, linked bus boards to each other, and a case DC entry to the supply, bus board, or PWR-DC12 outlets it feeds. A bond of 0 V to the chassis or earth is not row wiring; it follows PWR-008.

Terminals. Where a product takes or gives a rail or 0 V on row wiring, each terminal shall be an M4 screw, stud, or threaded standoff that clamps a ring terminal under a lock washer, rated for at least the current it carries, and the product shall publish the conductor sizes its terminals accept (PWR-005). That covers a supply's outputs, a bus board's input and its links, a DC entry panel's outputs to the supply, and the input of a product with PWR-DC12 outlets. A supply's terminal is marked with its rail or 0 V (SUP-003); EIS recommends the same marking on every other row wiring terminal.

Conductors. A row wiring conductor shall be insulated stranded copper rated 105 °C or more, with a crimped ring terminal at each end, of at least 18 AWG (16 AWG above 3 A, 14 AWG above 5 A, 12 AWG above 8 A, 10 AWG above 15 A), and shall carry no more than 25 A, a 0 V conductor carrying the larger of the +12 V and +5 V currents together and the −12 V current (PWR-006). A joint shall not rely on solder alone (PWR-006). A 0 V link may instead be a tinned copper braid with crimped or pressed ring ends, or a copper bar, of no more resistance (PWR-006). Metric wire meets the temperature rating as silicone (H05SJ-K) or 105 °C PVC; H05V-K and H07V-K are 70 °C wire and do not. Row wiring from a case DC entry carries what the adapter can deliver into a fault, not only the load: EIS recommends sizing it for the entry's published current, or fusing it at its conductor's rating. A wire nut, an insulation-displacement splice, a soldered strand under a screw, and a bare wire wrapped around a stud are not row wiring.

Resistance. Each row wiring conductor shall measure no more than 5 mΩ from ring terminal to ring terminal, and the 0 V conductor between a power supply and a bus board, or between linked bus boards, no more than any rail conductor beside it (PWR-007). The figure is Hinton Instruments' limit for supply cables, the place where one module's current couples into every other module's 0 V (Normative references). The table gives the longest conductor of each gauge that meets it, stranded copper at 1.05 times the ASTM B258 solid figure, allowing 0.25 mΩ for each crimp and its bolted joint; a conductor measured at 5 mΩ or less conforms whatever its length.

Bonds. Where a product bonds its 0 V to its chassis or to a protective-earth terminal, the bond shall be a conductor of at least 14 AWG, or copper of its own board of that section, landed by a ring terminal, a bracket, or a standoff on an M4 or larger stud or screw that presses metal GND-004 accepts under a toothed lock washer, or a bus bar of equivalent section (PWR-008). A DC entry panel whose board copper reaches its panel through brass brackets and ends at an M4 CHASSIS stud makes the bond that way (6.3).

An installer who joins a supply and bus boards from different makers wires them the same way (ASM-008, 9.1).

EIS recommends:

• an insulated or heat-shrink ring terminal sized to the conductor, with a 4.3 mm hole (M4 or #8), crimped with the ratchet tool its maker names;
• a split or toothed lock washer under the screw head or nut, or a screw with a captive one; at most two ring terminals on one terminal, back to back;
• terminals at least 14 mm apart, center to center, so that the widest ring a terminal accepts turns without touching its neighbor;
• a supply that ships its M4 screws and lock washers, and publishes their length and the torque for its terminals;
• stranded tinned copper, 105 °C PVC (UL 1015 at 600 V or UL 1569 at 300 V), or silicone (UL 3135) where the wire flexes;
• the supply placed close to the bus board's input, so that its conductors stay short, and the bus board's input near the middle of its headers;
• each rail conductor run together with its 0 V, bundled or twisted, to keep the loop small;
• a 0 V link (6.3) of 12 AWG or heavier, or a tinned copper braid or a bar of the same resistance (PWR-006), inside the 2 mΩ ASM-009 sets; the table gives the longest link of each gauge;
• red for +12 V, blue for −12 V, black for 0 V, and green-and-yellow only for an earth bond; EIS names no color for +5 V.

6.2 Power supplies

A power supply is the source of a power interface: for a row, or for the single product it is mounted on, such as the bus made on the back of a module from a DC rail (6.1). A bus supply feeds the row's bus board with the rails of 6.4: +12 V and −12 V, and +5 V if it provides one. A supply may be built into an enclosure or sold on its own.

The rules of this clause bind every outlet of a supply, whatever its interface; the limits that differ by interface are tabulated under Output quality. A supply that takes 12 V DC at a DC entry also keeps the entry rules of 8.1.

A supply of the DC rail

A power supply may provide the 12 V DC rail of 8.1 alongside or instead of the bus; it then has PWR-DC12 outlets, publishes the current of each outlet, and meets the outlet rules of 8.1 (SUP-009): an outlet to a module on a DC-BAR21 jack or a DC-VH2 header (DC-009), each protected separately (DC-012); an outlet to a distribution product's input may be an M4 row wiring terminal (PWR-005). Its claim file lists each outlet and each entry with its figures, including the DC entry of a supply fed from an external adapter; its claim line is EIS draft, power supply. Otherwise the 12 V of PWR-DC12 comes from an external adapter, which is outside EIS.

What a supply publishes

A power supply shall publish its ripple and noise on each rail it provides, peak-to-peak, measured as stated under Output quality (SUP-001). It also publishes the current it delivers on each rail, in total and at each outlet (PWR-002, 6.1).

Output connector and protection

An output on a plug-and-socket connector other than a power header, such as a wire-to-board housing or a DC plug, shall not mate with reversed polarity, a power-header outlet meeting the marking and keying of 6.4 instead (SUP-002), since an unkeyed ribbon socket enters any header. An output on row wiring terminals, the M4 terminals of 6.1, cannot be keyed and is exempt; each such terminal shall be marked with its rail or 0 V (SUP-003).

Each output rail of a power supply shall stay within ±5 % of its nominal voltage at its output terminals, from the minimum load the supply publishes on each rail to its rated current, whatever the load on its other rails within those limits (SUP-010): a cross-regulated triple-output supply drifts out of it when one rail is lightly loaded, and then publishes the minimum load that holds it.

Each output rail of a power supply shall survive an indefinite short to 0 V without damage, and shall return to its rated output when the short is removed, after an input cycle if it latches off (SUP-004). During power-up, power-down, or a short on another rail, no output rail shall be driven more than 0.7 V toward the opposite polarity (SUP-005); a Schottky clamp across each rail holds it at rated current. At start-up, no output rail shall overshoot its nominal voltage by more than 10 % (SUP-006). EIS recommends that each rail also survive a short to another rail, and that a supply with +5 V survive +12 V forced onto +5 V, which a 16-pin ribbon reversed at the bus end does (6.4).

A row is a large capacitive load, and a current limiter that cannot charge it within its on-time never starts. EIS recommends constant-current limiting, or a hiccup or foldback limiter whose maker states the capacitance it starts into, published with the supply's ratings. EIS recommends bringing the rails up in an order that avoids reverse stress on modules; SUP-005 bounds the reverse swing whatever the order.

Output quality

Each output rail of a power supply shall have ripple and noise below the limit in the table below for its power interface, 150 mV peak-to-peak on PWR-BUS, measured as stated below (SUP-007):

EIS requires no particular topology. EIS recommends a setpoint within ±1 % and load regulation within ±1 % from 10 % to 100 % load. A linear or post-regulated supply is typically under 5 mV, which suits a row of modules with VIDEO ports.

Ripple and noise are measured peak-to-peak on each rail:

• every rail at its rated current;
• a 300 mm (12 in) twisted pair from the rail's output terminals, or from test points the product publishes;
• the pair terminated at its far end by a 0.1 µF ceramic capacitor in parallel with a 47 µF electrolytic;
• the probe across those capacitors with a short ground spring, at 20 MHz oscilloscope bandwidth.

This is the method of common supply datasheets, Mean Well's among them, so one maker's figure compares with another's; the pair's inductance against the capacitors is part of it.

A supply for one product

A power supply mounted on the product it powers shall publish the heat it dissipates at its rated output and how far it extends behind that product (SUP-008). Like every power entry, it publishes the current it takes at its input (PWR-001); for a linear regulator on the bus, that is its output current plus its own. A module sold with such a supply publishes the currents and the depth of the pair. A supply that takes the bus keeps the power-header rules of 6.4 as a module does (BUS-008, BUS-009, BUS-019).

EIS recommends that such a supply's board fit the outline of a 1U module board (5.2.2): a parallel board no taller than 21.10 mm, with the 1U mounting-hole span of 33.65 mm (PANEL-009) behind a 1U panel. The same supply can then be mounted as a 1U module in a row that has one, or behind the product it feeds.

6.3 Grounding and 0 V

Every patch cable and every coaxial cable joins the 0 V of the two products it connects, so the products in a system share one 0 V whether or not anyone planned it. This clause makes that shared reference predictable: where 0 V runs in a row, across its power interfaces, how it meets protective earth, and how it reaches the next case.

In a row

A product shall connect every 0 V pin of its power headers, and the −V of its DC entry, to its 0 V (GND-001). The header's 0 V pins share the return current of all three bus rails, and a module that connects only some of them puts that current through fewer contacts. One 0 V gives a dual-source module one signal reference whichever entry is connected, and keeps a supply that takes PWR-DC12 and delivers the bus on one reference. An isolated power supply mounted on the product it powers joins its output 0 V to its input 0 V.

A bus board shall join the 0 V pins of every header to one 0 V that runs to the supply's 0 V terminal (GND-002).

EIS recommends keeping any panel-mounted part whose body touches the panel free of a connection to the module's 0 V; an insulated jack (7.1) meets that.

Return and reference

The 0 V of a row does two jobs, and EIS wires them differently.

• Return. Every module's current comes back to its supply through its bus board's 0 V and the board's 0 V conductor to that supply (GND-002). Each bus board has its own, a star from the supply, and never returns through another board: the drop on a return is that board's alone, and it does not move another board's reference.
• Reference. Every bus board's 0 V is the reference of every module on it, and a patch between two rows carries the difference between their references as signal. In a row with one supply, the board's copper and its return are the reference. With more than one supply, the returns end at different supplies, so where the bus boards of one enclosure are fed by more than one power supply, installation shall link their 0 V so that every bus board reaches, directly or through other boards' links, a bus board fed by each other supply, each 0 V link at most 2 mΩ terminal to terminal, and each bus board shall keep its own 0 V conductor to the supply that feeds it (ASM-009, 9.1). A chain of links along the rows does it; EIS recommends a grid, a link between every pair of neighbors, for three rows or more. The links hold every board at one potential whatever each return carries; the drop on a return then costs nothing but headroom.

A 0 V link is row wiring (6.1) on the boards' M4 0 V terminals; EIS recommends 12 AWG or heavier, or a braided strap or a bar, and the table in 6.1 gives the longest link of each gauge. A bus board may carry a 0 V strip, bare copper of its 0 V plane with a bus bar clamped on it, for the purpose (BUS-021, 6.5): its M4 holes, two rings on each, take its return and a link each way.

What a row's 0 V gains, in order: a bus board whose 0 V copper is a plane or a wide pour (6.5); 0 V links between the boards, which force one reference across supplies and across makers; a 0 V bar clamped on each board's bare 0 V strip, which takes the board's copper out of the path between its headers and its terminals; and the bar with the links.

One chassis tie

A system bonds its 0 V to the chassis, and the chassis to protective earth where it has one, at one point: the power entry of the case. A second bond gives mains-frequency and switching current a loop through 0 V, which shows as hum on audio and as slow horizontal bars on a picture.

A power supply publishes whether its 0 V output is connected to protective earth, and where (GND-003); a built-in supply publishes it in the enclosure's documentation. A product with a case DC entry publishes whether its 0 V is bonded to the chassis at the entry, and where (DC-014, 8.1). Mains safety, including the bonding of a metal case to protective earth, follows the safety standard the supply or case is certified to, not EIS.

EIS recommends that the product at the tie carry an M4 CHASSIS terminal, bonded to its 0 V or its earth in PWR-008's form and marked CHASSIS, so that straps to the case's other panels and metalwork land in one place; a DC entry panel is chassis where its screw heads press bare metal (Chassis continuity), and the terminal is for the parts that are not. A DC adapter whose output floats, the usual Class II desktop adapter, adds no second bond. EIS recommends that chassis ground carry only metalwork and screens, and bond to 0 V at the tie alone.

The mounting screws bond a front panel to the rails only where bare metal meets bare metal (Chassis continuity). With insulated jacks (7.1) the panel carries no signal return, and bonding the case metal to the supply's earth terminal, where it has one, is a shielding choice rather than a signal path.

Chassis continuity

Everything metal in a case other than the product at the tie is bonded to the tie only through the fasteners that hold the case together, and a fastener bonds two parts only where it presses conducting metal on conducting metal. Where a product makes a bond of a metal part to its 0 V, to its CHASSIS terminal, or to another metal part, and publishes it as a bond, the fastener shall press bare, plated, or conversion-coated metal, or a copper land clear of solder mask, not paint, powder coat, anodizing, or solder mask, and the bond shall measure at most 100 mΩ, and a bond of 0 V to the chassis (PWR-008) at most 10 mΩ (GND-004). The bonds it means are the ones a product publishes: a PWR-008 bond, a panel published as bonded to the rails, a strap, a link. The four-wire check is not the protective-bonding test of a mains product's safety standard, which a mains product still passes. An enclosure shall publish which of its metal parts, rails, inserts, sides, rear, and lid, are bonded to one another, and where its metalwork takes a bond to the row's 0 V (GND-005).

A joint either conducts, at a few milliohms, or it does not, at megohms, and no finish is conductive enough to carry a bond through it. The 100 mΩ figure is not a performance limit but a pass mark: the model in the eis-reference bonding page puts every metal-to-metal joint under 50 mΩ after years in a case, most under 10 mΩ, and every finished joint open. What a bond does for static, leakage, and interference depends on its length and width, not on its milliohms; what it needs is to exist.

EIS recommends:

• that a case bond every part a hand or a cable can reach: in the common wooden case with anodized rails and steel inserts the chassis is the inserts and the panels, and the rails float unless a bare pad or a strap joins them;
• that a part whose every path to the tie crosses a surface that does not conduct, or a loose fit such as an insert lying in an anodized groove, get a bare pad at one fastener, a conversion coating in place of anodize, or failing those a strap of PWR-008's form to the CHASSIS terminal or to a part already bonded, by the shortest route;
• that a module whose panel is to be chassis leave its front face bare under each mounting-screw head, a 7 mm disc at each hole on a coated panel or a finished copper land on an FR4 one; a coated panel with no bare spot is held by its screws and bonded by nothing;
• that a bond be checked four-wire at 1 A or more after assembly, from the CHASSIS terminal to the part.

Between cases

A patch cable or a VID-75 cable between two cases joins their 0 V through its sleeve or shell: a patch jack's sleeve is 0 V, and so is a VID-75 jack's shell (V75-002). A loop through two earth bonds shows as hum on audio and as slow-moving horizontal bars on a picture. EIS recommends:

• that the cases of one system take their 0 V from supplies that are all bonded to protective earth at the same outlet strip, or all floating;
• that a system spread over several cases, each with its own supply, join their bus boards' 0 V with a 0 V link, 0 V terminal to 0 V terminal, rather than through signal cables alone: 10 AWG or heavier, as short as the cases allow, and at most 2 mΩ where it can be, which on 10 AWG is about 0.44 m; and three or more cases as a grid rather than a chain, as Hinton Instruments' ZeroVolt link does with heavy cable and high-current connectors. ASM-009's 2 mΩ binds inside one enclosure, where a link that short can always be run.

Annex H turns the currents published under 6.1 into the heat of a row.

6.4 The bus

The bus (PWR-BUS) is the power interface most Eurorack rows are built on: +12 V and −12 V, and optionally +5 V, made by a power supply, carried by bus boards and power ribbons, and taken by a module at its power header. A product that takes the bus at a power header owes the rules of a PWR-BUS entry, and one that gives it at outlets the rules of a PWR-BUS outlet; a product with neither, such as a passive module, owes nothing in this clause or the two that follow except BUS-011, which binds every module (6.4).

This clause defines the rails, the power header with its pinout, marking, and keying, and what a module owes at its header. 6.5 adds the bus board and the ribbon, and 6.6 the CV and gate lines.

Rails

The bus shall provide +12 V and −12 V, and may provide +5 V, at every power header (BUS-001).

Header and pinout

A power header on a module or a bus board shall be a 2 × 5 or 2 × 8 pin header on a 2.54 mm grid, and a power cable shall end in IDC ribbon sockets that mate it (BUS-002). A power header on a module, a bus board, or a cable shall follow this pinout (BUS-003):

Some community tables give a different order, with +12 V on pins 7 and 8 and +5 V on pins 15 and 16. A cable or bus board made to such a table puts +12 V on a module's 0 V pins.

A module need not use the CV and gate lines; their levels and the rules for a module on them are in 6.6.

Marking and keying

The marked conductor of a power ribbon cable shall be −12 V, and on a module, a bus board, or a power supply it shall lie at the −12 V end of the header (BUS-004). A module, a bus board, and a power supply shall mark the −12 V end of each power header on the board (BUS-019), so that an unshrouded header can be oriented by eye at both ends.

A shrouded power header on a module or a bus board shall be keyed so that, viewed from the mating side with the −12 V end at the bottom, the key gap is on the right, and a keyed cable socket shall match it (BUS-005). The figure below is the reference view, and every header drawing uses it: pins 1 and 2 at the bottom, the gap centered in the right-hand wall. Shrouded headers in the field are keyed both ways, so a keyed cable from a conforming product enters a conforming bus board and may not enter another.

A module on the bus

A module powered from the bus shall draw only +12 V and −12 V, and may also draw +5 V (BUS-006). A module that uses neither +5 V nor bus CV or gate may use the 10-pin header (BUS-007). Like every power entry, it publishes its current on each rail (PWR-001).

A module or a power supply shall not draw more than 1.5 A on any rail through one power header (BUS-008), the charging of its decoupling at power-up excluded: each rail has two IDC contacts rated 1 A, and through a short ribbon they share the current up to about 2:1, so 1.5 A keeps the busier contact at its rating. A module that needs more uses a second header or a DC entry.

A module or a power supply shall tolerate reverse polarity at its power header without damage (BUS-009): a ribbon fitted backwards is the commonest field fault. Reversed at the module end it puts −12 V where +12 V belongs and the reverse, which a module survives with series diodes or a reverse-blocking regulator. Reversed at the bus end, a 16-pin ribbon also joins bus +12 V, +5 V, and CV through the module's 0 V pins, for every module on the board; the module cannot prevent that, and 6.2 recommends a supply that survives it. EIS covers only the pinout above and a reversed ribbon; any other voltage on these pins is outside EIS.

A bus cable supplied with a module shall be keyed so that it enters a shrouded header only with the marked conductor on −12 V (BUS-010). On a bus board whose shroud is keyed the other way, outside EIS, the installer fits an unkeyed cable with the marked conductor on −12 V.

Other headers

A header on a module that is not its power header shall either not mate a Eurorack power ribbon socket or tolerate one fitted to it, either way round, without damage (BUS-011). A header of a different pitch or connector family, or a shrouded header too small for the socket, meets it by not mating; a 2.54 mm header a ribbon socket fits, shrouded or not, meets it only by surviving a ribbon either way round, since an unkeyed socket enters any shroud; Annex G covers expanders and links.

Expander and link headers are often 2 × 5 or 2 × 8 pin headers on the same grid, and a power ribbon fitted to one puts ±12 V on its signal pins. A 2 × 7 header mates a 2 × 5 socket as readily as a 2 × 5 header does, so the rule reaches any rear 2.54 mm header, such as an expander link (Annex G).

6.5 Bus boards

The board in a row that carries the bus from the supply to the modules that take it at a power header. A row with the bus has one or more behind the panels, and an enclosure may build them in. Every header on a bus board is an outlet of the bus and meets 6.4: the rails, the header form, the pinout, the marked conductor on −12 V, and the shroud key.

Capacity

A bus board publishes its maximum current on each rail, in total and at each header (PWR-002). The per-header limit a bus board, a built-in bus board of an enclosure, or a power supply publishes for its power-header outlets shall not exceed 1.5 A per rail (BUS-012), the module limit of BUS-008.

Links and CV and gate regions

A bus board may split CV and gate into two regions (BUS-013). A bus board that splits CV and gate into regions shall mark on the board, and publish, which headers lie in each region (BUS-022). EIS recommends that a module publish whether it can transmit bus CV or gate. A link between two bus boards shall join CV to CV and gate to gate (BUS-014). How many modules may transmit on a line is a rule for assembling a system.

The board's supply input and its links to other bus boards are row wiring (6.1): M4 terminals that take ring terminals (PWR-005), on conductors of at most 5 mΩ (PWR-007), and its 0 V runs to the supply's 0 V terminal (GND-002).

EIS recommends that the 0 V copper from the board's 0 V terminal to its farthest header measure under 10 mΩ, a plane or a wide pour rather than a trace, and that the board take at least two 0 V links, on a second M4 terminal or a bus bar. The row wiring and the board carry the return current of every module on the board; a power ribbon carries the current of the modules on its sockets, through about 25 mΩ of 0 V at its 400 mm limit (BUS-015), its six 28 AWG conductors and the header contacts at each end.

A 0 V strip and bus bar

A bus board may carry a 0 V strip: a band of its outer-layer 0 V plane left bare of solder mask along the board's length, with plated holes at its mounting-hole positions, on which a 0 V bus bar is clamped by screws through the bar and the holes; the strip's end holes take M4, and a ring terminal under an M4 screw of the strip or the bar is a 0 V terminal of the board (BUS-021). The bar presses on the copper itself, with nothing between them but the finish, so the board's 0 V is the bar's the whole length of the board; the strip's M4 holes, two rings on each, give a board in the middle of a chain the positions one stud cannot, its return and a link each way (6.3). Without a bar the strip's M4 holes are still the board's link points.

EIS recommends:

• a strip at least 6 mm wide the full length of the board, on the plane's layer, finished as the board's pads are, beside the mounting holes rather than over them, with a plated M3 hole at every mounting-hole position, M4 at the two ends, and one more M4 position near the middle of a board longer than 42 HP;
• a copper bar, C110 or C101, no wider than the strip and under 0.5 mΩ end to end; the table gives the longest bar of each section. Brass is about four times the resistance and is not recommended. The bare strip alone, 70 µm (2 oz) copper 6 mm wide, is about 41 mΩ/m; the bar brings the board's 0 V under 1.5 mΩ/m, and under 1 mΩ/m from 6 × 3 mm up;
• a screw with a lock washer at every strip hole, torqued as the mounting screws are, so the joint stays under 0.1 mΩ for the life of the case; a ring terminal lands under the screw head, on the bar;
• the strip and the bar marked 0 V.

A set of bus bars, or a flying bus of row wiring, that feeds modules through cables ending in power headers or ribbon sockets is a bus board for EIS: it meets this clause and 6.4, with its M4 positions as its terminals.

Distribution on a bus board

A bus board may also distribute a DC rail or the video sync behind the panel; it then meets the rules of what it carries: the PWR-DC12 outlet rules of 8.1, or the video sync ports of 8.2 (BUS-020).

• Its PWR-DC12 outlets are those of 8.1, each protected (DC-009, DC-012).
• As a video sync distributor, it takes the video sync at a COAX-IN and gives each module a buffered copy at a COAX-THRU (8.2).

The claim line is EIS draft, bus board whatever it carries (4.2), and the claim file lists the outlets and ports. A board that carries no bus at all, only a DC rail or the video sync tree, is still a bus board, with no PWR-BUS outlets. Everything on the board shares its one 0 V (6.3).

Power ribbon cables

A power ribbon from a bus header to a module shall be no longer than 400 mm and shall use conductors of at least 28 AWG (BUS-015), the conductor of standard 1.27 mm pitch ribbon. A longer or thinner ribbon drops more at the header limit, and the drop comes off the module's rails: at 28 AWG (0.21 Ω/m), a 400 mm ribbon carrying 1.5 A on a rail drops about 65 mV in that rail's two conductors and about 30 mV more in their contacts at the two ends, about 95 mV; the 0 V return, six conductors and their contacts, about 25 mΩ, adds about 40 mV per 1.5 A it returns, up to about 75 mV with +12 V and +5 V both at the limit. A power ribbon cable sold on its own meets the marking and keying of 6.4 (BUS-004, BUS-005). The figures are in data/power_ribbon.json.

6.6 Bus CV and gate

The CV and gate lines of the 16-pin power header (6.4): when a module may use them, and their levels. Both follow A-100 practice.

A module shall listen to or transmit bus CV or gate only when a jumper or switch on the module is set to do so (BUS-016). A module that drives or receives bus CV shall meet the BUS-CV limits below (BUS-017), and one that drives or receives bus gate shall meet the BUS-GATE limits (BUS-018). At most one module transmits on each line, across linked bus boards (ASM-002). The patch classes are in 7.2.

• BUS-CV is 1 V/octave pitch CV, with the scale of PITCH, from one transmitter, such as a MIDI interface or a keyboard controller, to the oscillators that listen. It is not general control CV: an LFO or an envelope on it would detune every listening oscillator. The transmitter drives from an op-amp output through at most 100 Ω and holds 1.00 V/octave within ±0.3 % of scale at the header into 10 kΩ, ten listeners; each listener presents at least 100 kΩ.
• BUS-GATE is a 0 / +5 V gate that keeps the GATE contract: an output high at +4 V to +12 V and low at +0.5 V or less, and a listener that reads +3 V or more as high and +1 V or less as low. The transmitter drives through at most 2 kΩ, high at +4 V or more at the header into 4.7 kΩ, ten listeners; each listener presents at least 47 kΩ.

The lines are multi-drop, so the source impedance matters: ten listeners at 100 kΩ each load a line with 10 kΩ, and a 1 kΩ source into that load loses 9 % of scale, nearly an octave at the top of a 10 V range. Even 100 Ω loses 1 % into that load, so a transmitter meets ±0.3 % only by taking its feedback after the resistor or by using a smaller one; EIS recommends at most ten listeners on a line (9.2).

Class table

7.1 Signals

How a module declares what each port carries, and the rules every patch jack follows whatever it carries.

Port list

A module shall publish a port list naming, for every port, its signal class or unclassified, and for a video sync port its mode (8.2) (SIG-001). A module with no ports publishes an empty list. The port list goes in the manual, on the product page, or in a claim file. For each port it gives:

• its direction: in, out, or in_out for a port that is both, such as a bidirectional expander link;
• its class, or unclassified;
• the range it claims, when that is not the class default (7.2);
• for a COAX-IN or COAX-OUT, the formats it locks to or generates (8.3).

A port that claims a class meets that class's limits, in 7.2, and VIDEO's interface in 7.3.

A port that is neither a patch jack nor a video sync port, such as a coaxial picture jack, a line audio port, or MIDI, is listed as unclassified or by its Annex C class. EIS places no requirement on it beyond what this clause says of every jack. Its class is no patch class (7.2). EIS recommends that a 3.5 mm audio socket on the panel withstand a mono patch plug (patch safety).

EIS recommends labeling each port with its class, on the panel or in the manual.

Patch safety

These requirements apply to every patch jack on a module, whatever its class:

• A patch input shall withstand ±12 V indefinitely (SIG-002).
• A patch output shall withstand an indefinite short to 0 V or to another patch output (SIG-003).
• A patch output shall not drive the patch tip beyond ±12 V (SIG-004).

The ±12 V is the rails' nominal figure, applied from a source of 1 kΩ or less. A supply's 10 % start-up overshoot (SUP-006) is a rail figure: no conforming output drives a tip beyond ±12 V while its rails are anywhere inside the supply's limits.

EIS recommends:

• that a patch input withstand ±15 V, the rails of the ±15 V systems a patch cable can reach through an adapter;
• that every other 3.5 mm socket on the panel, such as a TRS MIDI, headphone, or stereo port, withstand ±12 V on its tip and a short from tip to sleeve, since a mono patch plug fits it;
• that every patch jack, and every RCA, BNC, or SMA jack, have its sleeve or shell insulated from the panel metal, so that no signal return runs through the panel and the case; 5.2.1 gives the construction on FR4 and on metal.

Patched signals only

A patch jack shall carry patched signals only: a module shall neither take nor give its video sync at a patch jack, and no patch jack shall list a format of clause 8.3 (SIG-015). The video sync is system configuration, wired once behind the panel at the video sync ports of 8.2, so patching never changes a module's timing. A timing pulse on a patch jack is a patched signal like any other (7.3).

A product that generates or locks to an external video sync shall take or give it at a video sync port on its rear (SIG-018), a COAX-IN or COAX-OUT of 8.2; a product with no such port neither generates nor locks to one.

Jacks inside the case

A jack inside the case shall not be a BNC jack: none at the rear of a module, on a bus board, or on a power supply (SIG-017). A BNC jack is on the outside of the case only, on a front panel or an enclosure's wall. A coaxial jack inside the case is an RCA, mated with a push, or an SMA, mated with a few turns of a small nut: a BNC's body and bayonet sleeve need room for fingers to grip and turn, which the space behind the panels and over a bus board does not give.

7.2 Signal classes

Every patch jack names the class of signal it carries, or unclassified (port list). EIS has seven classes: AUDIO, CV, and VIDEO, the signals a patch carries, with PITCH for calibrated pitch and GATE, TRIG, and CLOCK for timing. A module mixes them freely: a video module may take AUDIO, and an audio module may give VIDEO.

A port shall meet the limits of the class it names, at the range it names: an output keeps its full-scale signal within the range's ceiling, and an input accepts the range's full swing without clipping (SIG-005). The limits are in the class table.

Every patch jack keeps its safety (7.1), so a patch from one class into another damages neither jack; it only meets a level the input was not built for.

The shared interface

Every class but VIDEO has one interface: a source impedance of 1 kΩ typical and at most 2 kΩ, into a load of 100 kΩ typical and at least 47 kΩ. The worst conforming pair, a 2 kΩ source into a 47 kΩ load, loses 4 %. VIDEO has its own (7.3).

Each class has:

• a nominal level, what an output puts on the port;
• a full scale, the swing its range allows;
• a class ceiling and a damage limit (Terms);
• for gate, trigger, and clock, thresholds: what an input reads.

In the class table, a cell marked typical or recommended is a guide; every other figure is a limit (SIG-005). The levels are EIS figures; the gate thresholds follow A-100 practice (Scope 1.4).

Audio

AUDIO is Eurorack audio on a patch jack.

• Level: nominally ±5 V on the patch tip; full scale ±10 V peak at the default range B10, 7.07 V RMS for a full-scale sine. A port may claim B5 or B1 for a quieter signal.
• Coupling: AC or DC. An AC-coupled input passes 20 Hz within 1 dB; a DC-coupled output states its offset.

CV

CV is control voltage that is not calibrated for pitch: envelopes, LFOs, offsets, ramps, and the like. Its level is the range the port claims, bipolar or unipolar at 1, 5, or 10 V full scale. The default is B5, −5 to +5 V, which is what most control inputs and outputs are built for. An envelope from 0 to +8 V is CV at U10; a control on the VIDEO scale, 0 to +1 V, is CV at U1. A control port with a stated scaling other than 1 V/octave, such as Hz/V, is CV and names the scaling in its port list.

Pitch

PITCH is precision pitch CV: 1.00 V per octave within ±0.3 % of scale (3.6 cents per octave), over the span the port's range names. The default is B10; a 0 to +10 V sequencer or MIDI-to-CV output is U10, and a narrower span B5 or U5. The range states the span; the scale stays 1.00 V per octave.

EIS recommends:

• that 0 V correspond to C0 (16.35 Hz, MIDI note 12); every oscillator has a tune control, so the absolute pitch at 0 V is a calibration figure, not a requirement;
• that the manual publish the tracking error of a pitch output;
• that pitch ports be labeled 1 V/oct, so that they are not mistaken for video ports.

Video

VIDEO is video-rate signal on a patch jack, 0 to +1 V: pictures, ramps, keys, and control at the rate of a picture. Its interface, its paths, and its bandwidth are in 7.3.

Gate, trigger, and clock

GATE, TRIG, and CLOCK share one contract:

• An output drives high at +4 V to +12 V into 100 kΩ, and low at +0.5 V or less.
• An input reads +3 V or more as high and +1 V or less as low. EIS recommends at least 0.5 V of hysteresis between the two.

They differ in timing:

• GATE is a sustained high or low level. A run, reset, or start signal is a GATE.
• TRIG is a pulse at least 1 ms high (5 ms recommended). A TRIG input catches a 1 ms pulse.
• CLOCK is a repeating wave, high and low each at least 1 ms, at any duty. The product states the rate it accepts or produces and, for a tempo clock, the pulses per quarter note.

The gate line on the 16-pin header is BUS-GATE (6.6).

Ranges

A range is the full-scale swing a port is built for, named in the port list beside the class. The class table says which ranges a class takes and which is the default.

• A port that names no range has its class's default.
• A unipolar ceiling allows 20 % above full scale and 10 % below 0 V; a bipolar ceiling allows 20 % beyond full scale either way.
• An input accepts a swing when its gain at full scale is within 0.5 dB of its small-signal gain.
• Ranges do not relax patch safety.

EIS recommends that an output claim the smallest range that contains its full-scale signal, that an input claim the largest range whose full swing it accepts, and that a range other than the default be printed on the panel next to the jack.

Class table

The table is generated from data/signals.json. Every class is on a 3.5 mm mono jack. An impedance cell gives the typical figure and the limit; VIDEO's is a limit alone (SIG-009, SIG-010).

7.3 Video signals

Video on a patch jack, and the video ports beyond the patch field. VIDEO is a signal class like AUDIO and CV (7.2); its jacks are patch jacks and follow patch safety, and its interface is its own.

VIDEO

VIDEO carries video-rate signals on patch jacks: pictures, ramps, keys, and control. It is 0 to +1 V DC, range U1, with a ceiling of −0.1 to +1.2 V:

• A VIDEO input shall present 100 kΩ ±1 % to 0 V at the patch tip (SIG-009).
• A VIDEO output shall drive the patch tip through a 75 Ω ±1 % series resistor (SIG-010).
• A VIDEO input that reads a signal as high or low, such as a comparator, logic, or key input, shall switch at a threshold of +0.5 V: it reads above the threshold as high and below it as low (SIG-019).

+0.5 V is the midpoint of the VIDEO scale, so any VIDEO output drives any VIDEO logic input the same way, and a key or comparator splits a picture at mid-gray. EIS recommends that a VIDEO logic output give 0 V for low and +1 V for high, and a hysteresis of no more than 0.1 V, centered on the threshold, so that a slow ramp switches once and a fine picture is not coarsened. An input whose threshold is set by a control, such as a key level, meets SIG-019 at the control's marked center or default setting.

A 75 Ω source into a 100 kΩ load arrives at almost unity gain. The cable's capacitance and the input's set the bandwidth of the link (below), so EIS recommends an input capacitance of 30 pF or less. A control on the same 0 to +1 V scale is CV at U1, with the shared interface of 7.2; a VIDEO output drives it directly.

Video beyond the patch field

Video on a 75 Ω RCA, BNC, or SMA jack is not VIDEO:

• A video sync port on the rear is a COAX-IN, COAX-OUT, or COAX-THRU of 8.2, and lists the 8.3 formats it locks to or generates.
• A picture jack on the front, composite or component video, is listed in the port list by its Annex C class (VID-CVBS, VID-SVIDEO, VID-YPBPR, VID-RGBS, VID-RGSB, or VID-RGBHV) with the formats it carries. A digital port, such as SDI on a BNC jack, is listed by its Annex C class too.

A picture port has no rule of 8.2. EIS recommends that an analog picture port take the COAX-IN termination or the COAX-OUT back-termination of 8.2, so that it drives and loads a 75 Ω line the way a video sync port does.

Black, paths, and bandwidth

EIS recommends that a picture on VIDEO place black at 0 V and full scale (white, or a color channel at full saturation) at +1 V, so that a mixer or keyer can treat any two picture sources alike.

A VIDEO path is what lies between an input jack and an output jack of one module. A module shall publish, for each VIDEO output, the kind of path behind it and, for a linear or variable path, its −3 dB bandwidth measured as this clause states (SIG-016). The kind says whether a bandwidth describes the path at all:

In the port list:

• A path is linear when the module has a VIDEO input and the port list says nothing else, and a generator when the module has none.
• When a module has several inputs, the port list names the input a figure is measured from (from).
• Linear paths that share one figure publish it once, as a floor for them all (video.bandwidth_mhz), with any output that differs listed beside it.

Bandwidth is the −3 dB frequency of the path relative to its response at 100 kHz, measured:

• from a 75 Ω source at the input jack;
• into a load of 100 kΩ in parallel with 30 pF at the output jack;
• with a 0.5 V peak-to-peak signal about +0.5 V;
• with the module's controls at the setting that gives the widest response, which the port list names when it is not the default.

The three measurements of Annex A, a stepped sine, a step, and a multiburst, give the figure; the stepped sine settles a disagreement.

EIS sets no minimum bandwidth: a 1 MHz filter and a 100 MHz buffer both conform, each with its figure beside it. The figure says what the path does, not what a reader may do with it. Compared with a format's picture bandwidth, a path at or above that figure carries the format at full sharpness, and a narrower path carries it softer.

EIS recommends writing a bandwidth, in a port list and on a panel, as its bandwidth mark: BW and the figure in megahertz, rounded down to a whole number, so that a 35.7 MHz path is BW35. The mark is a number, never a format name, and two port lists compare at a glance.

EIS recommends that a module also publish, in the same port list:

• the delay of each linear or variable path, in nanoseconds, from an edge at the input jack to the same edge at the output jack;
• the rise time of each shaped path, 10 % to 90 % at the output jack;
• the bandwidth of each generator output, into the same load, although it has no path to measure;
• the input capacitance of each VIDEO input, which with the output's 75 Ω and the cable sets the bandwidth of the link;
• the Annex A method its figures were measured by (measured_by).

Delay matters when two copies of one picture reach a mixer by paths of different delay: they land side by side on the screen, offset by the difference, one HD sample per 13.5 ns at 74.25 MHz.

The patch link

A published bandwidth is the module's own; what arrives at the next module also depends on the cable. The output's 75 Ω, a patch cable of 100 pF/m, and a 30 pF input form one pole, whose −3 dB frequency falls as the cable grows:

On a cable of ordinary length, above about 30 MHz the link, not the module, is the limit. A stacked cable or a passive multiple adds a second cable and a second input to the same pole.

EIS recommends a patch cable of 100 pF/m or less, and that a maker of patch cables publish the capacitance per metre. A patch cable is not an EIS product; the figure is the cable maker's to publish.

Timing pulses on patch jacks

A video module's timing pulses on patch jacks, horizontal, vertical, field, burst-gate, or composite video sync, are patched signals like any other (7.1):

• a 0 / +5 V field or frame pulse is GATE;
• a line-rate pulse, too fast for CLOCK's 1 ms states, is unclassified, or VIDEO at 0 to +1 V;
• a 0 to +1 V composite video sync waveform is VIDEO.

A module may reset a ramp, key, or trigger from such a pulse. Its own raster timing, the formats of 8.3, locks to an external video sync only at a video sync port on its rear (SIG-015, SIG-018). A module that derives its line and field timing from a patch jack locks to a patched signal and does not meet SIG-015; it lists that jack by its class and has no video sync port for it.