[sdiy] VC Glide Circuit

Sun May 30 12:19:44 CEST 2021

On 30.05.2021 02:15, ackolonges fds via Synth-diy wrote:
> Thanks a lot to David and Quincas for recommending alternative designs.
>
> I found the Morphlag and DUSG schematics, and they look great, though 
> for my application I was hoping to make 8 of them to try to get that 
> nice polyphonic portamento sound out of my synth, and these designs 
> with separate up and down rates, and exponential/linear control seem a 
> little bit overboard for this... Also, for the Morphlag, I'd still 
> have to add in VC control, which for me would look like the OTA 
> section of the Unipole that I linked, and I'd worry that I'd be stuck 
> with the same issue if I don't understand what the problem is with my 
> current circuit.
>
> Thanks again for the comments - much appreciated, and if anyone has 
> any idea why my built circuits aren't able to achieve the fast glide 
> times of the simulation, I'd love to hear it.
>

It's just a wild guess, but R3 does delimit the maximum current that 
flows into the Iabc pin. Maybe go a bit lower 6.8k or so.

Are you running it on 15V as well? As a change in supply voltage will 
bring the maximum control current down also.

However these effects should not account for the big difference you see.

Have you measured the control current properly, i.e. with a meter in 
series to confirm the current source is working as expected?

Your current source maybe is oscillating. You should check that with a 
scope. To dampen, I would place a 1k resistor between the cap C2 and 
diode D1.

Best,
  René

> ------------------------------------------------------------------------
> *From:* Quincas Moreira <quincas at gmail.com>
> *Sent:* Saturday, May 29, 2021 9:13 PM
> *To:* ackolonges fds <ackolonges at hotmail.com>
> *Cc:* Synth-Diy mailing list <synth-diy at synth-diy.org>
> *Subject:* Re: [sdiy] VC Glide Circuit
> Can’t beat the Serge DUSG
>
> https://www.elby-designs.com/webtek/cgs/serge/cgs75/cgs75_vcs.html 
> <https://www.elby-designs.com/webtek/cgs/serge/cgs75/cgs75_vcs.html>
>
> Sent from my iPhone
>
>> On 29 May 2021, at 3:37, ackolonges fds via Synth-diy 
>> <synth-diy at synth-diy.org> wrote:
>>
>> 
>> Hi All,
>>
>> I wanted some VC slew for keyboard-style playing from my modular, so 
>> I searched for a circuit, and decided to try and build one called 
>> 'Unopole', - circuit diagram at 
>> https://thonk.co.uk/documents/stroh/Wiring/Unopole.jpg 
>> <https://thonk.co.uk/documents/stroh/Wiring/Unopole.jpg>
>>
>> The graph on the bottom right of the diagram shows a 0V to 10V signal 
>> slewing in 10ms, and I simulated the circuit in Falstad Circuit 
>> Simulator (text for circuit pasted at end), and it is slewing even 
>> faster. However, when I build the real circuit the glide is much slower.
>>
>> I've tried putting maximum current (2ma) to the OTA control pin, 
>> bringing down the value of the charging cap C1 to 10nF, and the 
>> fastest I'm able to get it to glide (at fastest pot setting and CV 
>> input together) is about 32ms from 0V to 1V, which is about 300ms 
>> over 10V.
>>
>> Below about 10nF for C1, the tuning of the 1V/Oct signal starts 
>> faltering. I'm using a ceramic C0G cap for this. Should I be using a 
>> different type of cap? If so, which would you recommend?
>>
>> Alternatively, does anyone have any ideas as to why I'm having 
>> trouble getting fast enough glides with this circuit? I've built it a 
>> few times with the same results. Or, has anybody on here built a 
>> different VC glide circuit that is more suitable?
>>
>> Thanks so much for any advice any of you may have.
>>
>> FALSTAD CIRCUIT
>> ------------------------
>>
>> $ 1 0.000005 11.086722712598126 17 5 50 5e-11
>> 174 48 128 48 208 1 100000 0.48020000000000007 Resistance
>> g 48 224 48 240 0 0
>> R 48 128 48 96 0 0 40 12 0 0 0.5
>> w 64 176 96 176 0
>> r 96 176 176 176 0 15000
>> r 96 240 176 240 0 10000
>> w 176 176 176 240 0
>> a 240 192 320 192 8 12 -12 1000000 0.000005472331080331692 0 100000
>> g 240 208 240 240 0 0
>> w 176 176 240 176 0
>> c 336 192 336 256 0 1e-10 -0.5472385803642495 0.001
>> w 320 192 336 192 0
>> d 400 192 400 256 2 default
>> w 336 192 400 192 0
>> w 176 240 176 272 0
>> w 176 272 304 272 0
>> w 304 272 304 256 0
>> w 304 256 336 256 0
>> w 336 256 400 256 0
>> w 400 256 464 256 0
>> t 432 224 464 224 1 -1 5.814783631368241 -0.5472385803642495 100 default
>> w 464 256 464 240 0
>> w 432 224 432 192 0
>> w 432 192 400 192 0
>> w 464 208 464 144 0
>> r 464 144 464 80 0 10000
>> 402 656 352 768 352 1 0\s0\s40\s-9\s0\s0\s0.5 0\s0\s40\s9\s0\s0\s0.5 
>> 0\s1\s-12.343529771373202\s0.5472335109924158\s100\sdefault 
>> 0\s1\s-0.5472335109924158\s0.5469786835162118\s100\sdefault 
>> 0\s1\s0\s0.5469786835162118\s100\sdefault 
>> 0\s1\s-8.547498288201437\s-4.257672077077218\s100\sdefault 
>> 0\s1\s-2.9215945571340436\s0.5469761486367535\s100\sdefault 
>> 0\s-1\s0.12505886554275492\s-0.14737295745119638\s100\sdefault 
>> 0\s-1\s0\s-0.14737295745119638\s100\sdefault 
>> 0\s-1\s17.405000677164992\s-0.12505886554275492\s100\sdefault 
>> 0\s-1\s0.5469710782877009\s-0.5467162500596725\s100\sdefault 
>> 0\s-1\s0\s-0.5467162500596725\s100\sdefault 
>> 0\s-1\s7.72624111758356\s-0.5469710782877009\s100\sdefault 
>> 0\s1\s0\s0.1634519859667556\s100\sdefault 
>> 0\s1\s-0.159115513874303\s0.1634519859667556\s100\sdefault 
>> 0\s1\s-8.857504054228007\s0.159115513874303\s100\sdefault 
>> 0\s1\s0\s0.10015101242435948\s100\sdefault 
>> 0\s1\s0\s-4.704497213289612\s100\sdefault
>> r 656 320 560 320 0 10000
>> R 560 320 512 320 0 2 100 5 0 0 0.5
>> w 464 80 752 80 0
>> w 752 80 752 320 0
>> w 768 352 800 352 0
>> c 800 352 800 416 0 8.2e-8 0.18007155406906683 0.001
>> g 800 416 800 432 0 0
>> w 800 352 848 352 0
>> r 672 496 752 496 0 10000
>> w 656 384 656 496 0
>> w 656 496 672 496 0
>> a 912 336 992 336 8 15 -15 1000000 0.1800697533715331 
>> 0.18007155406906683 100000
>> w 752 496 864 496 0
>> w 848 352 912 352 0
>> w 864 496 864 320 0
>> w 864 320 912 320 0
>> w 864 320 864 272 0
>> w 864 272 992 272 0
>> w 992 272 992 336 0
>> r 992 336 1072 336 0 330
>> g 96 240 96 272 0 0
>> o 28 64 0 4098 10 0.1 0 2 28 3
>> o 45 64 0 4098 10 0.1 1 2 45 3
>>
>>
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at synth-diy.org
>> http://synth-diy.org/mailman/listinfo/synth-diy
>> Selling or trading? Use marketplace at synth-diy.org
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org
> http://synth-diy.org/mailman/listinfo/synth-diy
> Selling or trading? Use marketplace at synth-diy.org

-- 
--
synth at schmitzbits.de
http://schmitzbits.de

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20210530/85690207/attachment.htm>