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Top VCA Tip
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julianw



Joined: Jul 30, 2007
Posts: 78
Location: UK

PostPosted: Thu Oct 18, 2007 11:39 am    Post subject: Top VCA Tip Reply with quote  Mark this post and the followings unread

I'm just ordering bits for Ken Stones Tube VCAs which I intend to put into my MOTM format modular and I thought I'd share this info cause I thin kits a great deal

As you know you can get the PCBs from Ken for $10 here:

http://www.cgs.synth.net/modules/cgs65_vca.html

The tube runs on a standard synth power supply no extra psu required

You can get the tubes mega cheap from http://stores.ebay.co.uk/urals-shop for $1.60 each ($16 for 10)

And now Scott at bridechamber has the 1U MOTM format panels in stock for $20

Add $20 of parts a bracket and sprinkle of skills and you have a really affordable MOTM format Tube VCA

I'm building 4 thumleft when the parts arrive, any one have an opinion on these?
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23isgood



Joined: Nov 18, 2006
Posts: 236
Location: San Francisco, CA bay area
Audio files: 13

PostPosted: Thu Oct 18, 2007 1:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have one of these. It really sounds great. You can get subtle grungyness which sounds nice or you can crank it up and get seriously crunchy. Its very warm. I need to pipe some drums into it, to hear what that sounds like. I should get a panel because right now its just the pcb with all the pots and jacks hanging off it.
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Dave Kendall



Joined: May 26, 2007
Posts: 421
Location: England
Audio files: 3

PostPosted: Thu Oct 18, 2007 1:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi.

Just built one, awaiting final wiring/testing. There was a thread on the CGS list where someone described succesfully using a DPDT changeover switch to alter the response - clean or dirty (that's roughly what it does, ... I think...) The switch connects either the 330K and solid line link on the pcb to the common pins of the switch, or the empty resistor space and the broken line.

REV1.1 boards have a pair of holes on the pcb near pins 1 + 2 of the tube, that effectively swap the 1 + 2 leads over. Ken wrote that it is OK to leave pins 1+2 in the "swapped" holes with this mod in place.
There's also a 200K trimmer (to be replaced by a resistor) between pins 6 + 7 of the LM358. At around 110K instead of the spec'd 220K, this should give a 0 to +10V range for the input CV over it's full range.
Temporary trimmers are also in the quality/gain position (8K2 or 27K max), and in place of the 100K gain adjust close to pin 2 of the TL072 on the schematic. Quality/gain *might* be worth a front panel pot - we'll see.....

On the prototype panel, I added a link from output to input, via a 100K pot. This is normalled to a pair of 3.5mm sockets, so that if feedback is not needed, or the module isn't in use, the pot can be used as a passive attenuator for something else.

It's about to go behind the hand labelled panel, which will eventually be printed ( If I can get the laser printer to work ...... Question )

cheers,
Dave


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