[sdiy] VC Glide Circuit

ackolonges fds ackolonges at hotmail.com
Sun May 30 02:15:22 CEST 2021


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.

________________________________
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

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

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


[https://thonk.co.uk/documents/stroh/Wiring/Unopole.jpg]

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