Soundtronics Breakout Boards for Synths

MFOS VCO 5U Synth Panel Breakout PCB Set

£8.42 incl VAT
(£7.02 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
  • 7210-734 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 VCO, you will need the following:

  • 7210-109 x 2
  • 7210-112 x 1

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

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

Parts needed

  • Assembled MFOS PCB #7210-001
  • Front Panel #7210-501
  • Back Panel #7210-801
  • PCB Holder #7210-901
  • 3-Way Pot PCB #7210-703 (2 reqd.)
  • 12-Way 1/4" Jack Socket PCB #7210-734
  • 12-way Cable Assemble #7210-112
  • 9-Way Cable Assembly #7210-109
  • PCB Holder Brackets Fixing Kit #7210-181
  • PCB Mounting Fixing Kit #7210-182
  • Additionally you will need our Switchcraft Jack Sockets #7212-210 (Pack of 10)

Panel PCB Preparation

PCB #7210-703 used for the coarse and FM depth controls require links B&G solder bridging.

PCB #7210-734 requires J7 solder bridging

Pot PCB Assembly

There are two pot PCBs to assemble, the one with the solder bridges (see above) has all three pots inserted wheras the PCB for the Fine Freq and PWM controls only has two pots inserted, middle position P3 is not used.

Make sure the solder bridges B & G are done before assembly as it is very difficult to solder G afterwards. Yes, I forgot as you may well spot in the pic below.

  1. Solder in JST headers noting that the slots in the socket housing point towards the top of the board on the pot
  2. Remove any anti-rotation lugs on the pots
  3. Insert pot into bracket and temporarily do up lock nut
  4. 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
  5. Repeat for remaining pots
  6. Remove pot nut

Socket PCB Assembly

General advice an assembling socket boards can be found on the PCB product page. Solder bridge J7 is required as it allows for a ground connection. Ensure the JST socket is also soldered in before the sockets. Sockets to solder in are:J1 to J6, J8 to J10 & J12

Panel PCBs Completed

You now have 3 panel PCBs populated and ready for assembly to the panel (front and back panels)


Assembly order is PCB mounting angle brackets, socket PCB, PCB with two pots on, PCB holder, 3-pot PCB, finally the main MFOS PCB itself

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:

2-pot PCB

  • Green
  • Orange
  • Yellow

3-pot PCB

  • Grey
  • Blue
  • Green

Socket PCB

  • Black going to J11 (note not the black wire on J1)

Inter-Panel Wiring

2 wires on the socket board are wired to the 3-pot PCB and suggest soldering these first. The grey wire goes to the top of the R9 position, The red wire from J12 goes to the top of the R6 position.

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

Socket PCB Cable

J12 Red R6
J11 Black Cut Off
J10 Brown PWM
J9 Grey R9
J9 Violet SYNC
J7 Blue GND
J6 Green CV3
J5 Orange SIN
J4 Yellow TRI
J3 White LIN
J2 Red RMP
J1 Black SQR

Note: R6 & R9 are on the 3-pot PCB, see above description.

3-Way 2-pot PCB

9 Grey R3P3
8 Violet R3P2
7 Blue R3P1
6 Green Cut Off
5 Orange Cut Off
4 Yellow Cut Off
3 White R39P1
2 Red R39P2
1 Black R39P3

3-Way 3 Pot PCB

1 Black R2P1
2 Red R2P2
3 White R2P3
4 Yellow Gnd
5 Orange CV1
6 Green Cut Off
7 Blue Cut Off
8 Violet CV2
9 Grey Cut Off

Once each wire is routed and soldered, it will be ready for dressing

We use 100mm cable ties to dress the cables.

The blue wire from the socket board and the yellow wire from the 3 pot PCB are wired to 0V Gnd on the MFOS board can be seen in the pic below. They are just above the two black electrolytic capacitors.

Wiring is now complete except for the +/-12V supply whcih 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. For tips on calibration, please see the VCO KB.

For interest only, the follow two pics show the current method against our previous method of panel construction which used an acrylic framework in place of both the aluminium back panel and panel PCBs.

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