[sdiy] Yet more questions: best VC drive approach

Jacob Watters jacobwatters at gmail.com
Thu Nov 8 21:52:42 CET 2018

I am working on a filter design (close to finishing the third and hopefully
final prototype) that uses a not-so-elegant, yet effective solution. I run
the integrators on a lower voltage, so that they clip very easily. Then, I
just use attenuation to control the amount of overdrive. This also ensures
that the clipping happens in the chip used for the integrators, and not in
the OTA's, which sound bad when overdriven.

*Jacob Watters*
Web & Multimedia Specialist
JacobWatters.com <http://jacobwatters.com/>
Tel: 226-886-3526

On Thu, Nov 8, 2018 at 3:32 PM Rutger Vlek <rutgervlek at gmail.com> wrote:

> Hi guys,
> I've been wondering about many things lately, hence the flood of emails to
> the list :). I also have to admit feeling a bit stupid about having to ask
> this.. but here goes:
> What's the best approach to designing a voltage controlled overdrive? The
> obvious solution I can think of is having a saturation element preceded by
> a VCA. While I haven't fully done my homework on it yet, my guts tell me
> that this isn't the best circuit in terms of noise behaviour, as it would
> require the saturation element to be at high gain constantly while the VCA
> various input level. Meaning that any VCA noise would be amplified by the
> full gain of the saturation element. In guitar stomp boxes, some design
> place a pot in the feedback loop of an opamp to change gain. Could a
> similar approach work well for a VC-drive unit and would it perform
> better/worse than the first solution I proposed?
> Finally, I've been thinking about making drive level voltage controlled
> via power supply to the saturation element (transistor in this case).
> Feeding the control voltage into a buffer that puts out the supply to a
> transistor would also allow to change drive level.
> What do you think? How it this typically done? I just bought a Novation
> Peak, and am impressed with it's three stages of overdrive although it
> suffers from noise issues due to the amounts of again at hand. It makes me
> wonder how I would design such a stage myself.
> Rutger
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