[sdiy] MS20 VCF clone troubles

[Jörg Schmitz]

Hi,

i have built this filter, and designed also a PCB for it, it works
absolutely perfect....
http://www.analog-synth.de/synths/mod2/ms20filter/ms20filter.htm
Don't know, whats wrong with your version....

Joerg.


----- Original Message -----
From: "Frederic Bourgeais" <fred at upian.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Monday, February 23, 2004 1:41 PM
Subject: [sdiy] MS20 VCF clone troubles


Hello All,

I build René Schmitz's MS20 vcf which can be found here:
http://www.uni-bonn.de/~uzs159/rs20.png

I have some troubles, all components value and connections has been checked
and rechecked.. Can you help me for debbugging ?

When no audio input is connected, Cutoff and resonnance pots seems to work.
I can heard the modulation on background noise, and the filter self
oscillate if I play with resonnance pot.

When I input audio signal into O1 inv.input, the signal don't seems to go
throw O1 output. I can heard again the modulation on background noise, and
filter can still self oscillate, but he don't process my input source...

I swapped all 3080 with new ones, but no way.. If I put audio in directly on
O1 output, or on A3 the filter seems to work..

Should I hear input signal at O1 output (I think ) ? 3080 are connected to
-15/+15, but i didn't linked the bias amplifier input (pin 5).. Should I
ground it ?

All the schematics has been build except CV2 input, and "Pitch input".
what's the difference between externals CV and pitch input ? What kind of
signal should I put in, ( voltage I believe, but can I leave them unplugged
) ?

I didn't use any CV source or pitch input, because 47k lin pot connected to
+15/-15 seems control the input voltage. Does this circuit can work like
that or I missed something ?

Thanks

Fred