[sdiy] Yet more questions: best VC drive approach

[Rutger Vlek]

Op ma 14 feb. 2022 13:04 schreef Spiros Makris <spirosmakris92 at gmail.com>:

>
> Although it's not what you are looking for, I found this paper very
> interesting in terms of describing and accurately tuning this non-linearity
> to make it work for you. http://www.openmusiclabs.com/files/otasine.pdf
>

That's a great paper indeed, I already encountered it a while back, when I
was reading about sine shapers, cusp cancelling and a new (or arguably
rediscovered) approach proposal by Don Tillman.


> On Sat, 12 Feb 2022 at 22:18, Rutger Vlek via Synth-diy <
> synth-diy at synth-diy.org> wrote:
>
>> Hi Richie,
>>
>> I hope you don't mind me bumping up an old thread. I was reading back
>> what you wrote in 2018 and wondered if you could refer me to more
>> background information on filter saturation. I'd like to understand what
>> happens in a ladder filter, and weather something musically similar could
>> also be recreated in other ways (e.g. in other topologies than a ladder).
>> If you have an opinion on the latter, please share!
>>
>> Regards,
>>
>> Rutger
>>
>> Op vr 9 nov. 2018 10:51 schreef <rburnett at richieburnett.co.uk>:
>>
>>> When you over-drive OTA based 1-pole "leaky integrator" stages, you
>>> actually get a signal dependent shift in the cutoff frequency as the OTA
>>> saturates, rather than what you would typically describe as "clipping".
>>> This behaviour is down to the way in which the OTA and filter capacitor
>>> are wrapped up inside a negative feedback loop.  The behaviour is quite
>>> like how the cutoff frequency of the Moog ladder filter changes
>>> dynamically with drive signal level.  It is much more musical that
>>> simple signal clipping.
>>>
>>> -Richie,
>>>
>>>
>>> On 2018-11-09 08:48, Rutger Vlek 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 [1]
>>> >> 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
>>> >>> _______________________________________________
>>> >>> Synth-diy mailing list
>>> >>> Synth-diy at synth-diy.org
>>> >>> http://synth-diy.org/mailman/listinfo/synth-diy
>>> >
>>> >
>>> >
>>> > Links:
>>> > ------
>>> > [1] http://jacobwatters.com/
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>>>
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