Diamante Fluttering Problem [SOLVED]

[Andrekp]

Hey, I built this using the suggested components. Subbed in 1N914's. but that shouldn't matter. Used the VTL5C3 work-alike from Small Bear (MIR10CLF-R).

It works fine EXCEPT there is a fast flutter going on. I checked all component values and it seems to be compressing as expected underneath the flutter. Less like dirt and more like a really fast trem.

I know a couple of people have mentioned something like this in the layout thread, but no solution has been mentioned.

Voltages all seem reasonable:
8.18V on the V+ pins of the IC's.
3.8-4.11 on the other opamp pins
GRND where it should be.

Collectors have 6.78V
Bases a few millivolts
Emitters at GRND

About a 1.43V drop across the Vactrol LED.

It's really like there's too much gain somewhere internally causing the Vactrol to pulse, or something.

Anybody else with this problem solve it?

I did try it at 18V, but it did not help.  I also switched the tannies to 2N3904, also to no help, though it may have changed it a bit.

Thanks
-Andre

[Andrekp]

OK, so as the circuit seemed to be working, other than the fluttering distortion, I figured that the most likely problem was the vactrol work-alike from Small Bear that I used.

I made a "vactrol" out of a GL5539 which I ordered from Amazon (of all places) and a yellow LED I had on hand.  This was intended to be close to the VTL5C3 needed.

This worked and there was no flutter, but the compression, while there, was not all that obvious.  I figured that my subbing in the lower gain 2N3904's to try to solve the fluttering, probably were too low in gain to drive the vactrol.  So I put them back to being the original 2N5088's, and the pedal seems to work as it should have from the beginning.

So, FWIW, if you build one of these - or probably any other optical comp - and get odd, fluttering output, the suspect is the vactrol.  

[IvIark]

Good info thanks for that