AC DC VCA Quick question

joshco · Joined: Nov 14, 2008 Posts: 55 Location: germany

Hello,
Currently I´m building some VCA´s, theres a DC and a AC Version.
What does this mean in general, are there any differences in sound or in amplification?

Thanks
best regards

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

The AC version is solely dedicated to process audio signals that's why there are capacitors in series with the INPUTS. These capacitors are there to filter out any DC component.

The DC version is more versatile because it can be used for processing either CVs or audio signals.

joshco · Joined: Nov 14, 2008 Posts: 55 Location: germany

Allright, the caps remove the dc signal in the audio material, whereas the DC version is able to amplify DC signals too.
Thank you!

robboten · Joined: Nov 26, 2009 Posts: 36 Location: stockholm, sweden

In the schematic for the simple VCA module there are two stars at the LED and the circuit around it. Does that mean that the LED only works with the AC version? That could explain why I get no light... And if so, is it possible to have light with the DC version as well?

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

If you have installed all these optional components and use it in DC mode then the LED can bright but only for a negative input voltage. The LED circuit was designed for AC only as indicated.

robboten · Joined: Nov 26, 2009 Posts: 36 Location: stockholm, sweden

Ah, I see. Thank you for your reply!

And also a big <3 for all your work on the modules you have published! I just love everything about them! The clearness of the pictures, the easy to follow schematics, the pcb-layouts and the functions. For me as a noob on the field this has helped me understand so much! Build my fourth module today (Noise, VCA, ADSR, S&H) and is so happy about it all! Next up is a mixer or the Steiner VCF. Probably ending up with all of them sooner or later... it's so much fun! So thank you again so much!

dancelwerk · Posted: Mon Aug 17, 2015 9:02 am Post subject:

Hi to all, I want to build the DC version but I have no clear what components I have to remove,

is * for the components AC and ** for the DC or viceversa?

I want to say, if I build the DC version, should i be remove Q4, D1, and C3 and C4?

thanks in advance.

Fernando.

alanwilder81 · Joined: Sep 03, 2016 Posts: 310 Location: italy

Hi all,

a big thanks to Yves Usson for delivering us such amazing material and schematics. i am trying to build my own synth, and i have a couple of questions regarding the student project supervised by T. Rochebois : building a small analogue synth

http://yusynth.net/index_en.php?&arg=1

has any of you ever built that nice CV GATE TRIGGER keyboard controller?

it looks amazingly simple and low components count.

if Yves or anyone else may give me a help, it would be greatly appreciated.
cheers Very Happy

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

Hi

No I haven't built it, but it was a student project that was successfully completed and the schematics published by Thierry were all tested therefore I guess you may be pretty confident in these. I see no flaw in them.

alanwilder81 · Joined: Sep 03, 2016 Posts: 310 Location: italy

hi gang,

i succesfully built the US1 VCA. It works,though exibits a very annoying "pop" or "click" on the beginning of the ADSR sound articulation.

Any ideas? thanks.

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yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

Either you didn't match the transistors of the differential pair or you did not adjust the trimmer correctly. Also you should use 1% tolerance for the resistors auround the second 741.