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MFOS VCO build problem
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author MFOS VCO build problem
speigel
I'm having trouble building a MFOS VCO from SOundtronics. I built the board fine, but I can't find any instructions on connections between the board and the pots and sockets. Can anyone give me a hand? Thanks, Speigel
khakifridge
It's all at MFOS (webpage for whole project or PDF for panel wiring).
speigel
Thanks Khakifridge, but I still can't find it. Have looked at every page on that site and its not there. The build instructions for the VCO do not have the FM1 & s controls.
Bodo1967
speigel wrote:
Thanks Khakifridge, but I still can't find it. Have looked at every page on that site and its not there. The build instructions for the VCO do not have the FM1 & s controls.


Looks a bit weird indeed. My guess is that they (Soundtronics or their suppliers, that is) simply labeled two of the three logartithmic CV inputs "FM Input" (there is also a panel layout on the MFOS site labelling all of the CV inputs as FM inputs) and added attenuators - in other words, pots as passive adjustable voltage dividers seriously, i just don't get it . Have a look at 'Oct-Attenuator' on the MFOS site, synth module section smile.

The PCBs appear to be the original MFOS ones so I doubt there's any substantial change to the circuit.
das_Produkt
I'm pretty sure that Bodo1967 is right.

Just to make extra clear what you have to do:
(I presume that you look at the back of your panel and the legs of your pot are looking upwards)
You have to wire the input to the right leg of the pot.
The left leg of your pot is connected to ground.
The middle leg has to be wired to a CV Input on the PCB.
sixbyseven
Hi Spiegel,

I just built 4 of these, and got the PCBs from Synthcube. The labels on the boards exactly match the labels on the diagram for the wiring on the MFOS site. Found here (just above the BOM) http://musicfromouterspace.com/index.php?MAINTAB=SYNTHDIY&PROJARG=CVNG TEXPANDER2015/CVNGTEXPANDER2015.php&VPW=1448&VPH=854


I am not sure by what you mean about FM1 and s controls though.

There is a synch in, a PWM input connected through R39 on the panel.

3 1V/Oct CV inputs and 1 linear CV input

Everything was straightforward. I believe the PCB should be at Rev 04

These VCO are awesome, stable and have a pretty good sine wave. I run two in my modular along with 2 TH-555s and a TH-X4046
Bodo1967
sixbyseven wrote:
I am not sure by what you mean about FM1 and s controls though.


s is a typo, that should read FM1 and FM2.

Check the Soundtronics product page, and especially the front panel offered there. You'll see what he (speigel) means wink.
sixbyseven
Thanks Bodo

Ok... I am catching on... it looks like this is modification somewhere along the line from a forum post here: https://www.muffwiggler.com/forum/viewtopic.php?t=154519&highlight=

and here: https://www.muffwiggler.com/forum/viewtopic.php?t=157305&sid=150dd4208 92f3092981bf8e66e47428f

It looks like it is just wired as an attenuator like you said.
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