Steiner calibration question

[dingebre]

I just built two Steiner Synthacon Euro version filters. I replaced the 2K2 resistor indicated with a trim pot because neither one would self oscillate.

I asked this badly the first time, sorry...

I would just like some advice on how to "calibrate" this trim pot. At what point do I want self oscillation? Do I really want it to oscillate? I"m not too keen on using it as a sound source.

Any thoughts would be appreciated.

Thanks,

David

[Tasmanian Alkaloid]

I don't know if this'll help, but i built an Elby version of the filter, and it required quite a fair amount of adjusting the two multi-turn trimmers to stop it from self-oscillating. But, i was amazed that it was a only a very fine window where it went from self-oscillation to 'normal' operation. Are you talking about the resonance trimmer? Laurie helped troubleshoot mine, and suggested that the optimum setting on the trimmer is somewhere around the middle. The trimmer used for Resonance in the elby version is a 2k multi-turn. The cv span trimmer also needed some adjusting.
From Laurie Biddulph-

"The following describes a quick (but dirty) approach to tuning this module as described by Ken Stone.

Initially, set the controls as follows:-

• Set CV SPAN TRIM (P206) fully anti-clockwise
• Set RESONANCE to maximum
• Set HP, BP and LP LEVEL to maximum
• Set CV LEVEL to maximum

• If required, adjust RESONANCE TRIM (P202) until the module stops oscillating
• Feed a LFO square wave (~5Hz, 10Vp-p 0V-centred) in to CV IN with no signal at the inputs
• Adjust CV REJECT (P201) for minimum thump
• Adjust the RESONANCE TRIM so that the screech can be controlled. It will depend on the initial
frequency pot setting somewhat, so you will need to tweak it so you have acceptable resonance at
the low frequencies, while not being uncontrollable or stoppable at the top of the frequency range
• CV SPAN ADJUST - adjust it so you get more or less one octave per volt. Don't waste too much
time here. There is no way it will be either accurate or thermally stable.

Be aware that unstable and "nasty" resonances are a feature of the Sallen-key filter "

-Matt

[dingebre]

Thanks, your commente do help a bit.

I read the bit on Ken's site about tuning, but it didn't make too much sense to me. Did you replace both the fixed resistors with pots or just "the one marked in red" the 2K2?

David

[Tasmanian Alkaloid]

I used a 2k trimmer for resonance & a 1k trimmer for CV span. I left CV reject empty. This was on the Elby pcb, though, and i'm not sure how these parts correlate with the CGS version.

[dingebre]

From what I can see, the schematics are the same.

Thanks for the information.

David