Synthacon Filter

Adam-V

Hi Guys,

I recently purchased a Synthacon filter module and I have a few issues with the way it is functioning (or possibly not functioning) and was wanting some feedback on how a synthacon filter should work and sound.

I have attached a small snippet of a simple sequence running through the the filter with the signal patched into the "ALL" input, slight modulation of the frequency via ADSR, BP level turned all the way down and HP/LP levels set at almost full and resonance and frequency set to about 3/4 full. About 25 seconds into the track I turn the cut off pot up slightly which accentuates the issue I have which sounds to me like the filter is randomly going in and out of self oscillation. Is this normal for one of these filters?

I am a little concerned by the build quality of the unit and the fact that when it arrived, the shaft on the resonance pot was bent so I am really unsure as to whether this is performing as it should or is in fact faulty.

Any feedback on this would be much appreciated as I need to decide whether or not to return the unit to the manufacturer.

Cheers,
Adam-V

Synthacon.mp3

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Synthacon Filter Sample

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andrewF · Posted: Tue Sep 18, 2007 8:09 am Post subject:

Hi
it doesn't sound right.
is this from Elby, using the CGS Euro-steiner PCBs?
there have been some problems with these delivering uncontrolled resonance.
Seems to happen most with 12V systems.

Have a look at the schematic, see the diodes in groups of three -
http://www.cgs.synth.net/modules/pic/schem_cgs35euro_steiner.gif
you want them in groups of two.
from Ken on CGS Yahoo -
"Further builds have discovered a problem when running the Euro version of
the Steiner design on 12 volts. If you wish to run on 12 volts and find the
module hard or impossible to set up due to uncontrollable resonance, short
out every third diode in the diode divider chain. It will still work on 15
volts with these diodes shorted out."

If its not Elby, ignore all this.

Seeing you paid for it, contact the manufacturer and get them to listen to your sample, most people in the synth business are keen do the right thing and will sort you out.

Adam-V · Posted: Tue Sep 18, 2007 3:34 pm Post subject:

Thank Andrew,

Yes it is an Elby CGS35 module. The diodes are in groups of two, there are links in the position of the third diodes. I'll contact Laurie and see what he says.

Cheers,
Adam-V

andrewF · Posted: Tue Sep 18, 2007 9:05 pm Post subject:

I'm sure Laurie will sort you out.
If you find the problem, let us know.