Arp 4072 VCF frequency pot issue

[lilpaula87]

Hi everyone,
I’m experiencing a problem with frequency pot in my new build, the arp 4072 filter. The frequency pot doesn’t work at all, it’s full opened doesn’t matter the setting I try. I’ve swapped pots in order to exclude a potentiometer failure. I’ve also temporarily removed cv’s and v/octave input just in case they influence somehow the filtering stage but without any result. As this is my second build I have not a big experience in DIY so could you guys please give me some ideas on how to fix this problem? Thanks in advance...

[gabbagabi]

Hi and to the forum.

first things first:
Usually "we" (at least me) are lazy baggers, so please always post the schematic in question or a link to it. So we dont need to search around ourselfs, even though yusynth circuits are quite famous.

It is always a good practice to post a close up from your build, one from the solder & one from the component side.

In addittion, please check if ALL chips have +/- Vsupply and GND on the right pins, please check that directly on the pin not on the solder point.
You could also check where the signal gets lost, so plug in a signal and try to follow it on the PCB, same with CV.

so far,
good luck, in bocca lupo!

[john trials]

I just built one of these modules a few months ago. Fantastic filter!

Mine did absolutely nothing until I carefully calibrated it. I thought I had made a big mistake. Before calibration, the sound coming out of the filter sounded exactly like the sound going in, no matter how much I rotated the frequency and resonance pots.

The voltage from the frequency pot wiper is summed with the CV and 1v/octave inputs, so if your filter reacts to CV and 1v/octave inputs, check the frequency pot connections.

One side of the frequency pot should be at +15 volts, and the other should be at ground. The wiper should vary between those two voltages as you rotate the pot (you may have to disconnect the wiper connection from the circuit to see this voltage change).

[AlanP]

I also found that this filter absolutely relies on calibration before it will filter.

[lilpaula87]

[john trials]

That is excellent that calibration fixed part of your problem!

For the resonant pot: Check all of the solder joints on the resonance pot to make sure that they are good (the solder joint is good, and they are wired correctly). Also, make sure that none of the wire connections are shorting to each other by accident.

The CW (clockwise) legs should be connected to each other, and the other side of the pot should be grounded together. Only the wiper connections are different from each other.

If that doesn't fix the problem, make sure your panel is not electrically charged. There is the possibility that a stray wire has contacted the panel. Ideally the panel should be at ground potential.

[lilpaula87]

Thanks mates for all your precious advices. Now I hope for good!