Archive of the former Yahoo!Groups mailing list: MOTM

Found a nifty patch which will allow for variable resonance on the
410 filters. If this has been covered before in this forum, one
thousand pardons.

In order to do this correctly, you'll need a voltage processor or
attenuator that's not AC coupled which can pass AC signals and
facilitate phase inversion of the signals passing through it. The
Blacet Mixer/Processor, Cynthia Octal Attenuator and Doepfer
A-138 polarizing Mixer are perfect examples. For ease of
reference, these instruments (or any others you have that serve
the same function) this will be referred to as the 'Processor' in
the patch below:

Patch:

Signal into Processor channel 1

Processor out into 410 signal input

Take any single filter output (out 1, out 2 or out 3) of the 410 into
Processor Channel 2 and to speakers.

By increasing the level pot of the Processor channel 2 in the
positive direction (positive feedback), the set resonance will
decrease. By increasing in the negative direction (negative
feedback), the resonance increases up to and into the poitn of
self-oscillation.

To test this, pull out the Processor channel 1 input , crank up the
negative feedback and bang - you're there. My scope's not by my
system right now, but it sounds like a clipped sine. Pretty
certain a resistor value change or two would easily remove this
clipping.

Obviously putting a VCA in line with the feedback loop will allow
for VC resonance.

You can also use the Mix out, but things tend to get a bit
comples, real fast. ADDING the Mix Out into the Processor
channel 3 along with a separate filter output seems a bit less
chaotic and will yield some interesting harmonic node points
when sweeping the 410 into higher resonance.

If you don't have an inverting mixer or processor BUT if your 410
has been fitted with Tony Allgood's 410 companion circuitry,
simply use a standard audio mixer and run the feedback through
Tony's inverter that comes with that mod before it leads its way
back into the 410. This set up won't allow for a decrease of
resonance, but it will let you increase it up to and past the point
of self-oscillation.

Enjoy (or not!),

- P