I finished to build my Shruthi XT with the Polivoks filterboard and have veeery low volume and the cutoff and resonance have nearly no effect.
I checked the board and all seems o.k. and also crossread the forum.
I checked all ±5V on the ICs and they are all fine
I choose the digital volume version and soldered the bridges on the controllerboard AND the filterboard.
The controllerboard works fine … Filter is set to pvk …
Some other users had similar problems with other boards and could find the error by testing the signal chain on the filterboard (a to g).
can someone please point me to a documentation where I can find these testing points and values for the polivoksfilter?
Thanks a lot, Sascha
I don’t think there is exactly that info for this filter. There is this page http://mutable-instruments.net/shruthi1/build/polivoks
You could also post a picture of both sides of your board here.
I found this http://mutable-instruments.net/wiki/Checking_the_signal_path
in the wiki and will try to follow that path on the polivoks
Some multimeter-testing on the signal path with init Sound standard C note
OSC -> 2.45 Volt
VCA -> 3.3 Volt
TL072 Pin 1
> 0V ?? Pin 8> 0.07 V
Point 7 … th 10k at the LM13700 -> 0.033V
TL084 -> Pin1: -0.3V / Pin 7: -2.8 V / Pin 8: -1.3 V / Pin 14: 3.4V
Will do some more checks on the solder points and find out WHY Pin 1 of the TL072 is 0V
For checking the signal path in de Polivoks you need to look at the schematics of the polivoks filter.
The signal path in the SMR4 filter is totally different on the PCB. Except point 1. It’s good to check that you have signal there.
Multimeter won’t help you in the signal path. It can help to check if the CV’s are coming in the right places.
For checking the signal path use a scope or make a probe that is connected to an audio amp so you can really listen what’s going on.
Finally solved …
when I shortened the collector and base of Q3 I got sound and resonance but no cutoff …
So the filter was permanently closed …
The connection on Filterboard from F to the 56K resistor was broken. Bridged it and now it works …