[sdiy] Odp: Pink?

[mskala at ansuz.sooke.bc.ca]

On Tue, 21 Aug 2018, Rutger Vlek wrote:
> resonance responses. A nice test to perform is to plot the maximum
> self-oscillation amplitude at a fixed resonance level and sweep the cutoff.
> Some filters show serious roll-off towards high frequencies, which I find
> extremely musical. The Yamaha CS filters are a great example. Tracking
> inherently suffers as a consequence though. I suspect a small phase shift

This was something I encountered during development of my Leapfrog design.
On the breadboard, it couldn't oscillate over the full frequency range.
The range over which it could maintain oscillation, and the consistency of
level over that range, improved both when I took it from the breadboard to
an etched PCB, and when I switched from silver mica to polystyrene
capacitors.  I think multiple effects were involved, including stray
capacitance in the breadboard and low-frequency misbehaviour of the silver
mica caps ("soakage" - they're not really a good choice for audio), either
of which could affect the alignment between the multiple integrators,
changing how much amplitude comes out at a fixed feedback level (and in
the extreme, whether it will oscillate at all).

-- 
Matthew Skala
mskala at ansuz.sooke.bc.ca                 People before principles.
http://ansuz.sooke.bc.ca/