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 Forum index » DIY Hardware and Software » Thomas Henry designs
Trouble Shooting my VCA-1
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wvanderveen



Joined: Dec 01, 2018
Posts: 2
Location: United States

PostPosted: Sat Dec 01, 2018 6:34 pm    Post subject: Trouble Shooting my VCA-1
Subject description: Built two successfully, last one giving me fits
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Hi all,

I am new to the forum and somewhat newish to DIY synth, but I've heard great things about Thomas Henry's designs so I decided to give the VCA-1 a shot. I built two of them that work just fine, but number three is giving me some troubles. Do these symptoms sound familiar to anyone? Thanks for any insight!

For some reason, no signals plugged into the inputs make any noise, except in the case of inputting a pulse wave and setting the initial gain to just the right spot - then suddenly the pulse wave (and no other type of wave) will pass through. If I plug said square wave into a CV input, a ton of audible noise bleeds through.

I have gone to town with my multimeter, probing everything, and swapped out the TL071 and TL072 with known good chips, and the behavior hasn't changed at all. I have done a side by side comparison with a known good example of the entire module and can't tell what's different/wrong.

One other thing - when probing I realized that I hadn't soldered in the ground connections to pin 3 of the TL071 or pin 5 of the TL072. I swapped the ICs after correcting the problem, but is it possible that powering the modules without those connections may have blown a diode, transistor, or the OTA?

I'm normally the self sufficient type, but I've tried everything (and searched all the relevant threads on this forum) and I'm at the end of my rope. Any help is very much appreciated!

Best,

-Wesley

EDIT: Link to VCA-1 Page: https://www.birthofasynth.com/Thomas_Henry/Pages/VCA-1.html

Last edited by wvanderveen on Sun Dec 02, 2018 2:13 am; edited 2 times in total
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g.gabba



Joined: Nov 29, 2008
Posts: 464
Location: berlin
Audio files: 23

PostPosted: Sun Dec 02, 2018 1:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello wvanderveen, and welcome to the forum

let me quote here our forum-member Grumble:
"You will notice that if you add (at least) a link to the schematics of the module concerning your question, that you get more ánd a better response to your question."

cu, gabbagabi
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wvanderveen



Joined: Dec 01, 2018
Posts: 2
Location: United States

PostPosted: Sun Dec 02, 2018 2:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Apologies - edited ^__^
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