[sdiy] SVF question

[Tom Wiltshire]

On 4 Oct 2011, at 03:39, Andrew Simper wrote:

> Yes, the diodes prevent self oscillation, and for low resonance (high
> damping) they are bypassed almost completely. Note that if you allow
> signal to flow through the feedback route from the bandpass output to
> the input of an SVF you lower the resonance, so the diodes are placed
> so that they limit resonance for high signal values.


You can set it up with enough feedback from the lowpass output that the filter will oscillate, but with enough damping from the bandpass output that the oscillation won't get driven into clipping. Since the diodes set the point at which that extra damping kicks in, they're a key part in this, but the weights on the feedback paths are also crucial.

The same problem came up some time ago with SSM2164-based SVF designs. It's tricky to balance it just right.

Tom