Soundtronics Breakout Boards for Synths

MFOS Dual AR 5U Synth Panel Breakout PCB Set

£11.18 incl VAT
(£9.32 exc. tax)
200.00 g.
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We find that wiring a MFOS PCB to the front panel controls is both time consuming and often detracts from the overall finish. We are not able to alter the MFOS PCBs to make panel wiring easier so we approached the problem from a different angle. We chose to mount the front panel controls on a mini PCBs (breakout boards) that take the panel controls to a JST type XH socket into which is plugged a lead (not included with set but available separately). This lead is then dressed to the main MFOS PCB (or sometimes to other panel controls) and soldered into the respective pads. Many breakout boards have solderable jumpers for making common connections as well as thin tracks to cut where panel mounted resistors need to be connected inline with say a pot wiper. MFOS projects may require multiple breakout boards so we bundle these altogether and offer them in one ST Synth Panel Breakout PCB Set. The pack description will further describe the wiring colour code and what if any links need to be made or cut.

This method does have other advantages other than just time saving and appearance:

  • Time saving
  • Neater more professional appearance - improves resale value
  • Takes care of common connections between panel components
  • Has space to accommodate panel mounted resistors and capacitors
  • Can improve reliability - have you tried soldering a diode, LED and a wire to one pin on a toggle switch on the 16-step sequencer?
  • Makes fault finding easier

If you have any reservations about using connectors, then simply solder wires direct to the breakout boards. Takes longer but you still get all of the other advantages.

The boards are designed to fit our front panel component spacing so you will see references to pitch and whether it is in the 'x' or 'y' or both direction. At the time of writing, there was 30+ breakout boards developed for pots (using pot brackets), sockets (jack and banana), switches and LEDs. Whilst these will not take care of every panel component on over 40 MFOS projects, it will go a long way to achieving it. As we work through making up each MFOS project with these breakout boards, we will see where improvements can be made or even create more breakout boards to provide the best possible solution.

The panel PCBs can also be used with our YuSynth range. YuSynth PCBs are better laid out as regards panel wiring but can still take advantage of these breakout PCBs.

This pack contains the following breakout PCBs:

  • 7210-703 x 2
  • 7210-721 x 2
  • 7210-750 x 1

Whilst you can solder wires between the breakout PCBs and the main PCB, we do recommend using our JST cable assemblies. For the Dual AR, you will need the following:

  • 7210-109 x 4
  • 7210-103 x 2

See the Build Guide tab for wiring information on how to use these breakout PCBs with this module.

Guidelines when building a Dual AR module using our panel PCBs, front and back panels, PCB holder and the MFOS main PCB.

Parts needed

  • Assembled MFOS PCB #7210-021
  • Front Panel #7210-521
  • Back Panel #7210-821
  • PCB Holder #7210-921
  • 3-Way Pot PCB #7210-703 (2 reqd.)
  • 2-way Socket PCB #7210-721 (2 reqd)
  • AR Toggle Switch PCB #7210-750
  • Pot Brackets #7300-000 (6 reqd)
  • 3-way Cable Assemble #7210-103 (2 reqd)
  • 9-Way Cable Assembly #7210-109 (4 reqd)
  • PCB Holder Brackets Fixing Kit #7210-181
  • PCB Mounting Fixing Kit #7210-182
  • Additionally you will need our Switchcraft Jack Sockets #7212-204 (Pack of 4)

Panel PCB Preparation

Two PCBs #7210-703 used for the Dual AR, one for each channel. The boards are handed so we suggest marking the boards as AR1 & AR2. The first task is to cut option links as we need to solder in two resistors.

For AR1 cut R8 and for AR2 cut R2 as indicated by the blue arrows below.

Next, solder in the two 9-way JST sockets noting that the slots face towards the top of the PCB. Solder in the 1k resistors into position R8 on AR1 and R2 on AR2. On AR1, solder bridges B & C. On AR2, solder bridges A & E.

Next solder in wire links as follows:

AR1 PCB R2 to R3, R5 to R6

AR2 PCB R5 to R6, R8 to R9


Pot PCB Assembly (see photo above)

  1. Remove any anti-rotation lugs on the pots
  2. Insert pot into bracket and temporarily do up lock nut
  3. Insert pot with bracket into PCB and solder in position ensuring the pot bracket sits flat on PCB. Only solder the bracket lugs on the bottom of the board
  4. Repeat for remaining pots
  5. Remove pot nut

A special panel PCB #7210-750 was designed for the dual AR. Solder in the tantalum capacitors 1uF in C3 & C22, 4.7uF in C4 & C23. Then solder in the two 9-way JST sockets with their slots facing upwards.

Solder in the 3-way JST sockets to the jack socket PCBs 7210-721 noting the correct orientation


With the front panel and aluminium back panel together, fit the toggle switches, push button switches and the jack sockets. Ensure the orientation of each is as per the photo below. Place the toggle PCB over switches, ensure it is level and then solder all of the connections. 

Place the jack socket PCBs on the sockets and solder in place. Mount the completed PCB to the PCB holder and then fix to the front panel using the 'L' brackets noting the correct way around in the photo below. Do not fully tighten the M4 screws to the aluminium panel just yet.

Install the pot PCBs ensuring AR1 & AR2 are put in the correct position. Now you can tighten the mounting brackets.


Panel Wiring

With the assembly of the Panel complete, it's time for the wiring.

Firstly, plug in the JST cable assemblies, they will only go in one way around as they are keyed.

Not all of the wires are required so we suggest cutting them off at the plug.

Cables not required are:

AR1 3-pot PCB

  • Red
  • Orange
  • Green

AR2 3-pot PCB

  • Orange
  • Green
  • Violet

Socket PCBs

  • Yellow on both PCBs

Inter-Panel Wiring

Most wires go to the main MFOS PCB but some connect between the panel PCBs which are described in the wiring schedule tables below.

Now the remaining wires can be dressed and soldered to the main PCB. We tend to route the wire first to get a final length before cutting. The cut end is then stripped and tinned and placed into the respective pin on the MFOS PCB. With a fine tipped soldering iron (<1mm), we then solder the wire in position from the top of the PCB. We each have our own preferred method but this works well for us.

Wiring Schedule

AR1 pot PCB Cable

1 Black ATK1
2 Red Cut
3 White CMN1
4 Yellow REL1
5 Orange Cut
6 Green Cut
7 Blue Ground on MFOS PCB
8 Violet To R1 position on AR1 jack socket PCB (see photo above)
9 Grey ARO1


 AR2 pot PCB Cable

9 Grey CMN2
8 Violet Cut
7 Blue ATK2
6 Green Cut
5 Orange Cut
4 Yellow REL2
3 White ARO2
2 Red To R1 position on AR1 jack socket PCB (see photo above)
1 Black Ground on MFOS PCB


AR1 Socket PCB

1 Yellow Cut
2 Black X2* pad on the toggle PCB
3 Red Ground pad on AR1 pot PCB

AR2 Socket PCB

1 Yellow Cut
2 Black X1* pad on the toggle PCB
3 Red Ground pad on AR2 pot PCB

*Update 25/3/18 X1 and X2 now corrected, thanks Dado for pointing this out.

Toggle PCB U1 Connector

1 Black MG2
2 Red +12V
3 White Connect to bottom pad of R5 on AR2 pot PCB
4 Yellow RP2A
5 Orange RP2B
6 Green GTA2
7 Blue GTB2
8 Violet GTD2
9 Grey GTC2

Toggle PCB U2 Connector

1 Black MG1
2 Red Ground on End of AR1 pot PCB
3 White Connect to bottom pad of R5 on AR1 pot PCB
4 Yellow RP1A
5 Orange RP1B
6 Green GTA1
7 Blue GTC1
8 Violet GTB1
9 Grey GTD1

Wiring is now complete except for the +/-12V supply which depends on your own system. We solder in a 3-core cable with a plug on the end which we use for power distribution in our racks. Next is a visual inspection and we also apply power before inserting chips to check for correct polarity across one of the IC sockets.

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