Ang: [sdiy] MS20 VCF clone troubles

[Daniel Araya]

I have had the same problems my self! 
If I recall correct I found out that the output from the buffer A1 should go to the positive input of O2, not the negative as in the schematic.
It is also very simple to also get a highpass response from this filter, see http://www.ele4music.com/vcf8e/vcf%208e.pdf

regards

/Daniel Araya



>>> Frederic Bourgeais <fred at upian.com> 2004-02-23 13:41:57 >>>
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