Can anyone with a 101 do me a big favor and look inside their pedal to see the value of capacitor 26? it is located just to the right of where the cutoff pot connects, when you are looking at the board with all the written text right side up. mine is missing.
If I’m reading it correctly, it is marked 224 and then just below that E5M. If it follows standard cap code, 224 would be a value of .22uF. But you should check with tech support at Moog Music, they will help you (they have helped me in the past).
How did the cap turn up missing?
tech support did help me out too, which i wasnt necessarily expecting. they said the same thing. i got the filter after someone had already converted it to a module for a synth. they did a kind of messy job. It seems to work fine except the cutoff range is not right. at the lowest cutoff setting there is still significant signal passing, even some high frequencies. about midway some higher frequencies cut out, and all the way open it behaves as you would expect.
Looking at the board i noticed that c26 was not there. i replaced this with a .22uf this morning but it doesnt seem to fix the problem. so i’m still tinkering around to see what might be causing this.
Thanks for your help
No problem, glad to be of help.
Moog is very good with customer service and response. They will not release schematics (as many companies prefer not to do), but they have assisted with DIY circuit mods that I asked about.
That’s too bad about the bad mods to your filter. I hope the seller informed you about those mods. It sounds like there may have been some other component changes. Can you get in touch with them about this?
You mention that you can still hear high frequencies even with the cutoff set low. That sounds like the Mix control and/or the Envelope Amount control may not be set right or working properly. With the Mix knob set to max and the Amount set to minimum (and nothing connected to the Cutoff or Mix input jack) the Cutoff knob should be able to sweep the full range of the filter. Another test (using the same settings) is to set the Resonance knob to max so that the filter oscillates. The filter should produce a subsonic low frequency with the Cutoff knob set to minimum and sweep up to a very high frequency at max. If you have a scope or meter, you can also check to make sure that the voltage on the wiper of the Cutoff knob is about -5V at the minimum setting and +5V at the max. The same values for the Mix knob. The Amount and Resonance range from about 0V to +5V.
i actually picked this up a few years ago with a bunch of other modules and i’ have no way of getting in touch with the modder.
Your right. the problem is not the cutoff. the problem is with the mixing, as some of the original mix comes through regardless. when it is at all over driven the filtered signal can not be heard at all. the voltage on the mix pot seems fine so im not really sure what is going on.
guess i will see if tech support has anything to say.
Here is something else that you could try – with the Mix knob set to max – apply +5V to the Mix input jack to see if you can force more of the filter sound versus the original sound.
Since the Mix knob generates a CV (as opposed to crossfading the audio signal directly) and there is a CV Mix input jack, I suspect that the mix circuit might be two VCAs, one for the original sound and one for the filter sound. One gets the CV straight, the other gets an inverted CV signal. If that is the case, it appears that maybe the original VCA is not shutting off completely for some reason. Can you tell if the original sound volume changes at all with different Mix knob settings?
right again,
i hooked up an envelope generator to the mix cv and was able to get a pure filtered signal.
with the mix control on the minimum setting the volume of the signal is slightly louder.
Interesting…
If my VCA sound mixing circuit theory is correct, then for some reason the original sound VCA is not getting enough CV control from the Mix knob to shut it down completely. If my theory is correct, then there is a CV mixer for the Mix knob voltage and the Mix input jack voltage. There may be a component change (or damage) by the previous owner in that CV mixer circuit, or of the VCA itself.