Vermona Perfourmer filter envelope amt mod

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Vermona Perfourmer filter envelope amt mod

Postby plus321 » Mon Mar 23, 2015 12:11 am

Hi, I just got a Vermona Perfourmer. It's a cool synth. I noticed for some reason the filter envelope amount knob doesn't really have a strong effect on the filter. So I was looking at the schematics and messing around and found there is a 330k resistor at the mixing part into the filter. I can change this resistor and get a stronger envelope and the effect I'm looking for, but I'm wondering if this is bad in the long term. I imagine they set it this way for a reason, but who knows.

The mod wheel in is similarly weak. It would be nice to get these modulators to utilize the full filter range. I guess I'm just hoping somebody out there who knows about electronics will tell me it's okay.

You can see the inputs and resistors in the lower left corner of the screenshot.

https://www.dropbox.com/s/lxemzyc1oaz01 ... fschem.png
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Re: Vermona Perfourmer filter envelope amt mod

Postby meatballfulton » Mon Mar 23, 2015 1:06 pm

Former Perfourmer owner here.

If you set the filter totally closed, the EG or the mod wheel should be able to sweep it fully open. If it can't, time for a calibration.

Perfourmer service documentation (schematics, trimpot diagrams)
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Re: Vermona Perfourmer filter envelope amt mod

Postby plus321 » Mon Mar 23, 2015 3:49 pm

Yeah, it's kind of strange none of the modulators will open the filter 100% if the cutoff is all the way down. They are all kind of weak.

I was looking over the documents and I don't see any kind of adjustment for the filter other than resonance. I measured the env voltage going in at the filter summing point and found it was really high before the 330k resistor (8v which I think is the high level of the filter). I was messing around with lowering that resistor value and found it worked out pretty well. Just wondering if changing these values could cause damage.

Or is there some other filter calibration that I'm missing? There is a trimpot on the env board, but I thought it was just a fine tune for the filter env amount knob.
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Re: Vermona Perfourmer filter envelope amt mod

Postby meatballfulton » Mon Mar 23, 2015 5:04 pm

Damage? Not likely.
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Re: Vermona Perfourmer filter envelope amt mod

Postby plus321 » Tue Mar 24, 2015 11:32 pm

I just swapped out the resistors. Sounds cool. I did email Vermona asking if they had anymore documents about the tuning and scaling and I haven't got a response.

Any chance you remember it?

I got it kind of close, but still needs a little work. I understand most of the trimmers; the scale, tuning, -2 octave and I think the other one is for tuning range on the faceplate tune knob. Just wasn't sure what to do with the 'high-end' trimmer which might be why I can't get them all dead on.
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Re: Vermona Perfourmer filter envelope amt mod

Postby Yekuku » Wed Mar 25, 2015 1:05 am

Although I have a perfourmer , I cant really comment about the Filter ENV Amount because It has been in storage for many years now.
Last time I had it opened up , it was when I was trying to add custom CV I/O , but since I had no schematics of the main board and the CV expansion , I had no success doing so.
I would recommend to replace the 330K resistors with trimmers eg. 680K , tweak and find the range that you are looking for and then replace trimmers with the appropriate resistors.
Maybe later on the weekend I can dig it out and test the Filter env depth, if I manage to do so , I will let you know.
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Re: Vermona Perfourmer filter envelope amt mod

Postby meatballfulton » Wed Mar 25, 2015 12:05 pm

Perfourmer is V/oct scaled. Since the filter range is probably around ten octaves, the sweep range should be about 10 volts. You can measure that with a voltmeter or scope easily enough.
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Re: Vermona Perfourmer filter envelope amt mod

Postby plus321 » Wed Mar 25, 2015 2:02 pm

Yeah, I have the filter doing what I want it to do. Now I am interested in finding out what the 'hi-end' trimmer does in the osc tuning and scaling section. I still haven't got a reply from Vermona.
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