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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
tube vca modifications and results
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sonicwarrior



Joined: Dec 22, 2005
Posts: 223
Location: Cologne, Germany

PostPosted: Sun Aug 26, 2012 2:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Aum Generator wrote:
you changed only one on the schematic and left the other 100k, because you wanted only one cv input. right?


Yepp.

You can see the standard bias setting on the picture of my stuffed PCB above. I stuffed the jumper on the left side.
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Aum Generator



Joined: Aug 15, 2011
Posts: 11
Location: Bratislava

PostPosted: Sun Aug 26, 2012 2:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

sonicwarrior wrote:
You can see the standard bias setting on the picture of my stuffed PCB above. I stuffed the jumper on the left side.


ah, i (think i) know what you mean now. That bias jumper is marked well on the silkscreen of the v1.1 PCB and explained on cgs site. That picture I used is just older. Updated in the original post / redrew to look like the v1.1 now.
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otherunicorn



Joined: May 11, 2008
Posts: 136
Location: Australia

PostPosted: Thu Jan 10, 2013 9:09 pm    Post subject: Re: tube vca modifications and results Reply with quote  Mark this post and the followings unread

PrimateSynthesis wrote:
LED's are very noisy. Since the cathode is in the signal path, I eliminated the two signal diodes, the two LED's, and their 1.5K resistors.


This comment has being bugging me for a while. LEDs are frequently used as voltage references, and recently I saw one recommended for a reference in a critical application. A little poking around led me to this http://www.diyaudio.com/forums/parts/35821-some-noise-measurements-leds-zener-diodes-post417008.html#post417008 which you need to log in to see, but the gist of it is common red and orange LEDs are only up to 2 times as noisy as a forward biased low-noise transistor or a 1N4148. That isn't very noisy. We are looking at around 0.25 to 0.35 uV. Green isn't as good. Blue is awful at 3.2 uV (10 times as much).

Red LED being referenced is Kingbright L934ID - T-1, a 25mcd LED.

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