Constant drift of Steiner Parker filter cutoff frequency

[stanft]

Hello everyone,

I wanted to ask if any of you have noticed similar behavior. My PolyBrute 12 is actually super stable regarding tuning. I calibrated it a few times after purchase. Since then, the oscillators and the Ladder filter are super stable. But the Steiner-Parker filter is worrying me. Even after warming up (approx. 30 minutes), I still have extreme fluctuations between the individual voice cards (fluctuations of almost 90 cents). One voice card stands out particularly.

After a calibration, the tuning is then within the expected range (approx. 5 cents deviation). You can’t expect more from a Steiner-Parker filter. But that doesn’t last long. Fifteen minutes later, there are already larger deviations again. This means that the Steiner-Parker filter would actually need to be calibrated continuously on my PolyBrute.

Is this expected behavior with the PolyBrute? I would have thought that at least after warming up, the Steiner-Parker filter should also be reasonably stable. Or do I possibly have a defect, since one voice card in particular always drifts very strongly?

Best regards,
Stephan

[DrJustice]

While Steiner Parker is the wild child of the filters, it tracks nigh on perfectly here (the ‘wild’ character only being in the sound now), or as perfect as you can expect from a filter.

Just to test this I’ve had the PB12 powered up for a couple of hours now. I’ve set the SP and Ladder to full resonance and turned off the oscillators. Both filters tracks well across the whole keyboard range, playing in tune with each other with only some slight variation in beating. The voices are pretty much bang on similar. I’m not sure how much the variation is in cents, but it’s no more than 4-5 or so I reckon. It’s good enough to play melodies with both filters oscillating without any “sea sick” feeling.

I last calibrated it around the time of its launch, and there has been no need for further calibration. I’m impressed with how well the oscillators and filers stay in perfect tune.

So, if your SP filters are 90 cents out between voices, and you can’t get them to track well by calibrating (have you tried the debug mode calibration?), then I think you should contact support.