[sdiy] Yet more questions: best VC drive approach

Jacob Watters jacobwatters at gmail.com
Tue Nov 13 16:38:49 CET 2018


Oh ok! That makes sense. Thanks for clarifying that. I will need to give
this a try.


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


On Mon, Nov 12, 2018 at 7:20 PM Tom Wiltshire <tom at electricdruid.net> wrote:

> The problem might be that you’re overdriving the OTA itself by maxing out
> its gain. The “nice” distortion from OTAs come from overdriving the
> differential inputs for a smooth tanh curve distortion. This is what Craing
> Anderson does in the Device article Terry B. posted. There are two CA3080s
> used. The first controls the drive level sent to the second. The second is
> a fixed gain, and is used just for its pleasant input distortion.
>
> Tom
>
> ==================
>        Electric Druid
> Synth & Stompbox DIY
> ==================
>
> > On 9 Nov 2018, at 12:15, Jacob Watters <jacobwatters at gmail.com> wrote:
> >
> > Yes in the VCA and not the integrator. I find that OTA's don't sound
> nice when overdriven. They have a crackly, noisey sound. I prefer to do my
> overdriving in a 4069, like the wasp filter.
> >
> > On Fri, Nov 9, 2018, 3:48 AM Rutger Vlek, <rutgervlek at gmail.com> wrote:
> > Hi Jacob,
> >
> >
> >> 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.
> >
> > I presume you refer to the OTA in the VCA that controls the drive level?
> Or do you mean OTAs inside your integrators? In the latter case I don't
> understand what you're saying (sorry)...
> >
> > Rutger
> >
> >
> >> Jacob Watters
> >> Web & Multimedia Specialist
> >> 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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> >
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>
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