Issues with 4730 VCF, 4720 VCO
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Author:  patrickvf [ Mon Nov 18, 2013 1:11 pm ]
Post subject:  Issues with 4730 VCF, 4720 VCO

I finally got around to replace most of the modules of my first Paia with the 4700 type modules from the other one, plus a 4780 sequencer and 4720 VCO, which I both purchased on Ebay.

The VCF has the following problem: When I patch any of the waveform outputs of the VCO into the VCF, there is no output. The filter itself works, because I routed the gate/trigger signals from the sequencer in to the filter's CV inputs, which produced pops that were affected by the filter upon messing with the cutoff and Q settings. However there appears to be something going wrong between the input and filter circuit. I hope that I don't have to replace any of the extremely rare parts (transducers, ca39xx, etc. ) Any suggestions for a quick fix or easier to find equivalent parts?

The VCO is another story - I bought this from a seller who claimed that it was stable and perfectly tuned, but it is far from stable, and the PWM
(once again) does not sound as it should (distorted, fuzz like), but at least it tracks properly. Any suggestions on improving the stability of the VCO and/or what could be causing the issue?

P.S: Because of the way the sequencer was constructed, I had to remove the rod tha held the power rails, and replaced the rails with European style connector terminals, which makes it a bit easier to move/replace modules (at least I don't have to break out the solder iron all the time), could that be part of the problem? Everything else seems to work just fine.

Author:  patrickvf [ Wed Nov 27, 2013 3:40 pm ]
Post subject:  Re: Issues with 4730 VCF, 4720 VCO

Turns out both work fine, at least they did after reworking the power supply and testing them as the only modules in the system, but after stuffing the rest of the modules in the synth, the VCO doesn't do squat and only makes sound when I touch the tip of the CV plug. Didn't see anything loose on the module nor the connections.. now what?

Author:  toneman [ Wed Nov 27, 2013 7:09 pm ]
Post subject:  Re: Issues with 4730 VCF, 4720 VCO

Now, you'll have to troubleshoot!!

U R a troubleshooter!

I R a troubleshooter 2!

Don't get in trouble while U R troubleshooting :shock:

check ALL solder connections with magnification.
check voltage at the test points (TP)--see schematic.


Author:  patrickvf [ Wed Nov 27, 2013 8:41 pm ]
Post subject:  Re: Issues with 4730 VCF, 4720 VCO

Hmmm... why would it work that time and then not now? Could it be really as simple as funky solder joints? Guess I'm going to have to check that out then, eh? Meanwhile I'm going to replace it with the old VCO that was there in the first place to see if it's not something else after all. I'll keep you posted..

Author:  patrickvf [ Fri Nov 29, 2013 10:29 pm ]
Post subject:  Re: Issues with 4730 VCF, 4720 VCO

Before I forget about it - I replaced the 4700 VCO with the old 2700 VCO, and that one works fine, so yeah I'm gonna check the solder joints, etc of the 4700 VCO. I hope that I don't have to spend too much time on it. It still mystifies me that it worked fine when I tested it after recapping the power supply, and now it's shot after hooking up the other modules *grumbles*

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