Eurorack panel components

This information is for doing DIY, or repairs on Eurorack front panels. It's not comprehensive, everyone has preferences, but attempts to cover the commonly used parts and what sort of things will work.

Avoid cheap parts, especially if mechanical. Invest in quality, you always get what you pay for. Otherwise your entire system might later develop intermittent faults. Vertical mount front panel components will need to of a similar height to neatly fit the gap between the PCB and front panel.

In order to construct low profile/skiff friendly Eurorack modules vertical mount components are required. These allow the PCB to be mounted parallel to the front panel, keeping module depth to a minimum.

Eurorack panel specifications
The Eurorack format was developed in parallel by Analogue Systems and Doepfer, with different approaches to module power connectors and front panel mounting holes. These days the Doepfer standard predominates. The format is based on [//en.wikipedia.org/wiki/Deutsches_Institut_f%C3%BCr_Normung DIN] 41494 Eurocard standard.

Doepfer specifies the Eurorack front panel material as 2 mm anodized aluminium. In practice panels from other manufacturers may slightly differ, e.g. Synthwerks use the closest gauge that Metalphoto offer which is 0.0625" (1.59 mm). Also check data sheets for front panel parts, e.g. the maximum recommended thickness for 3.5 mm Cliff 1384 jacks is 2.5 mm. Front panel dimensions in the the 3U Eurorack format are specified in U and HP not in inches or millimeters. One U (unit) or in German HE (höhen einheit) is 1.75 inches equivalent to 44.45 mm. Thus the panels height is 5.25" (133.35 mm) less any allowance for mounting rail flange. Width is measured in HP (horizontal pitch) or in German TE (teilungs einheiten); 1 HP is 1/5" (0.2", 5.08 mm or 200 mil). The actual width of a front panel is a few tenth of a mm less than whatever multiple of 5.08 mm it is, to give some tolerance for final assembly. A 19-inch rack has a usable width of 84 HP.

The vertical distance between the mounting holes on Eurorack rails is 122.5mm apart (4.823"). Based on the manufacturer's drawings for the most common rails used in Euro cases, the clear space between pairs of rails is: These don't include a tolerances for the screw hole in the panel or for the nut in the rail. These can cause the rails to be closer or further apart when any given module is tightened in. It's better to give a little more clearance than suggested by these figures.
 * Schroff, 112.2 mm (4.415 inches)
 * Gie-Tec, Proma (now defunct) and TipTop Z-Rails, 112.5mm (4.429 inches)
 * Vector, 115.1mm (4.531 inches)

Panel mounting holes
If the Doepfer specification is followed, or rails with sliding nuts are used, elongated holes are not required. These are useful for non-standard panel widths and to compensate for for manufacturing tolerances of the panel width or hole position. They help to fit the modules flush against one another. In a double width case, there will be a gap where the two threaded inserts meet, unless e.g. single 168 HP tiptop Z rails are used.

Oval holes were originally for mixed Analogue Systems (AS) and Doepfer systems. The AS holes are 0.2" from the panel edge and the Doepfer holes are 0.3" (7.62 mm) from the edge. The oval holes were originally used to allow these modules to be placed in the same threaded rows without having the 1/2 HP gap that would otherwise result. These days the oval holes are mostly just centered on the Doepfer spacing.

For front panels up to 10 HP (2 inches) two mounting holes are sufficient, wider than this and four mounting holes are usual. To attach the modules to the mounting rails M3x6 DIN 7985 cross recessed pan head machine screws are used. The mounting hole diameter is 3.2mm (0.13"), centered 3mm from top and bottom edges and 7.45mm from the left edge. The right hand mounting holes are an increment of 5.08mm, (1 hp) from those on the left. It is normal for left and right holes to be at different distances from the panel edges.

Blank panels
See Eurorack DIY parts#Blank panels

PCB dimensions and mounting
These days Eurorack modules tend to mount the PCB parralel to the front panel, held in place by the pots, jacks and switches. Modules with wired front panel components cost more to manufacture than PCB mounted, however these electro-mechanical components have limited lifetimes and while PCB mounted parts can be repaired it's not as easily as wired components. Also PCB mounted components mean the board is designed around specific parts. If any of these parts goes out of production the modules have to be redesigned, with the additional cost of updating the PCBs.

To fit between the mounting rails the maximum vertical PCB size can be from 108mm (4.25") to 110mm. The width of the PCB needs to be a touch less than that of the front panel, whilst allowing for clearance and taking tolerances into consideration.

Stacked PCBs
Stacked PCBs can be connected with standard 0.1" single and double row male/female pin headers. These combine to a height of 7/16 inch or 11mm and boards can be mounted to each other with spacers of this length.

To cut the headers, don't use tools you value highly, these are made of brittle glass filled epoxy which will damage the edge of any blades used to cut it. To get the single row male headers to length, grip the last pin of the length you want firmly in pliers and snap the rest off. The female headers don't snap easily so first pull the pins out of the body at the point where you want it to snap, then file the ends smooth. Alternately combine smaller lengths to make up the length required. To get them to butt against each other at 0.1" if there is extra plastic on the ends file it down.

Suitable parts can be purchased for example:
 * 517-929974-01-36-RK, Mouser female 2.54mm pin header, 36 way, tin plated copper
 * 517-834-01-36, Mouser male 2.54mm pin header, 36 way, tin plated copper
 * 855-R30-1001102, Mouser M3x11mm hex spacer. Fit to the PCB with M3x5mm machine screws.

Component layout
Choose between having jacks easier to read placed near their associated controls, or below where patch cables are then easier to keep out of the way.

Design the panel so that behind the panel the component bodies have enough clearance from each other and in front both the controls and the users fingers have enough room to operate. Also check that any close to an edge won't interfere with mounting the panel into its enclosure. Check the angle of rotation of the pot will match the scale going to be marked on the panel.

Doepfer and Analogue Solutions both use 20mm (0.8") vertical spacing between pots.

Behind the panel leave 10 mm clear from top and bottom edges for panel mounted components to clear the rails.

3.5mm jack sockets
3.5mm jack sockets are not 1/8 inch. Popular brands of vertical mount 3.5mm mono jacks for Eurorack are Cliff (used by Doepfer), Erthenvar aka Flight of Harmony, Kobiconn (used by Cwejman, Make Noise, Malekko and Metasonix) and Switchcraft. These are available switched (for normalisation) and unswitched. Erthenvar 3.5mm vertical mount jacks with a thread diameter about 5.9mm (0.232"), will fit well with panel drill holes of 6.0 to 6.5mm diameter. Suppliers:

Cliff horizontal PCB mount

 * Newark:3.5mm mono PCB jack socket
 * Rapid:3.5mm mono PCB jack socket

Vertical PCB mount
Vertical mount 3.5 mm jack sockets are hard to find. Options include:
 * Cliff, used by Doepfer
 * Erthenvar 3.5mm vertical mount jacks, switched
 * Jalco YK21-5157 and variations. 10.5mm high versions and in mono, unthreaded bush
 * Mouser:Kobiconn 16PJ138
 * Farnell:Lumberg 1502 03 looks like a wired chassis socket with solder tags, it also has a PCB template
 * QingPu, available from Thonk:
 * WQP-PJ3410, plastic bush
 * WQP-PJ3010BM, metal bush model with two ground lugs. PCB to panel gaps of 9.0 to 12.0 mm look feasible, with the lower values achieved by bending the four feet diagonally or at 90 degrees.
 * WQP-PJ301M-12, an alternative to Kobiconn 16PJ138, all PCB mount pins, with the reliable beryllium copper spring
 * Rapid:TruConnect PJ-360, stereo, unthreaded bush
 * Mouser:Kobiconn 161-0352-EX, stereo, 3.5 mm

Wired/panel mount

 * Mouser:Kobiconn 16PJ138, mono 3.5mm, switched

Banana sockets
4 mm banana sockets and jacks aren't normally used on unmodified Eurorack, banana jack socket are unshielded but CVs don't need shielding and because audio levels are usually high, this won't be a problem. When patching into external synths or other devices use a shielded cable with both ends of the shield connected to ground. Banana sockets are cheaper because they are mechanically simpler. They are also much more durable since there is less to go wrong. They are widely available and come in a range of colours. Banana plugs are stackable i.e. one can plug into the end of another. Most banana synths are designed with stackable plugs in mind, whereas most 1/4" and 3.5mm jack systems include multiples. Regular jacks provide an extra switched connection enabling normalization (connections when there is no cable plugged in).
 * Mouser
 * Bushing used where the PCB is parallel to the panel and there isn't enough room behind for the length of the shaft of the banana jack. Obviously this arrangement will protrude further out from the front of panel. Approximate measurements: .32" id, .4" od, .3" high.

Horizontal PCB mount

 * Mouser:311-1902F
 * SmallBear:PC Mount Right-Angle potentiometers
 * SmallBear SKU 1012A
 * Tayda SKU A-1847

Vertical PCB mount

 * Thonk:Alpha 9mm Pots
 * Mouser:Alpha RK12L types
 * Mouser:BI Technologies 10.5mm high linear pots
 * Bourns:
 * PDB12-M, PCB mount, 9mm high, no thread, 12mm package
 * PTV09A-4
 * Farnell:3310Y series, 5mm deep with 6mm of thread so may be too low to be used easily
 * PTV111-3 7.5 mm high body with 5.0 mm high bushing, available with centre detent
 * Digital continuous encoders for microcontroller based products
 * Vishay:
 * P12 series 11mm to panel
 * P9 vertical mount 7mm high with 7mm bushing, only up to 10V

Wired/panel mount

 * SmallBear SKU 0221C1
 * Jameco 317236
 * 0.55" 136241
 * 19.8mm 264990
 * 33.3mm 264946
 * Mouser 633-M201901-RO
 * SP3T toggle switch 633-M202402-RO
 * 633-FB15ANEP2

Rotary switches

 * Small rotary switches by Grayhill, e.g. Grayhill miniature 8 position rotary 706-50P36-01-1-08N, Mouser
 * Alpha 8 way vertical mount, Mouser
 * NKK MR series, Mouser

LEDs

 * Mouser 3mm LED 593-2000C (C stands for clear)