[sdiy] Formant 24dB filter

[Magnus Danielson]

From: Brown David <David.Brown at tms-ltd.com>
Subject: [sdiy] Formant 24dB filter
Date: Tue, 5 Jun 2001 10:53:23 +0100 

Hi David,

> Has anyone who has built the Formant 24dB filter had a problem when the
> filter tries to go into oscillation?  My filter seems to work perfectly well
> most of the time, but if the 'Q' control is set to maximum and the Frequency
> knob turned up, the filter just latched up rather than oscillates.
> Admittedly, the construction manual states that a resistor in the feedback
> circuit should be chosen so as to avoid oscillation.  However it doesn't say
> bad things will happen if oscillation starts?

My Formant's 24dB filter has the same problem. I have only thougth
about it some, but have not spent quality time on it. I too want to
wash out this problem out of my Formant.

Let's work on this together. I'm eager to learn what others have for
an experience on how to attack this and naturally how well people
disciplined thier filters.

I beleive high frequency sweep speed caused the latchup, but it is
some time since I tried it. However, I love when that filter slowly
sweeps over the overtones when the Q is HIGH.... hehehe...

Cheers,
Magnus