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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
Tube VCA/Wavefolder
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neandrewthal



Joined: May 11, 2007
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PostPosted: Mon May 12, 2008 10:08 am    Post subject: Tube VCA/Wavefolder Reply with quote  Mark this post and the followings unread

I see a lot of people are building the CGS65 Tube VCA/Timbral gate but there is not a lot of info on the CGS37 Tube VCA/Wavefolder. I accidentally purchased the board for the latter instead of the former and was wondering how the two compare and if someone has any tips on where to buy the CV4014 tube or an equivalent. Thanks.
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neandrewthal



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PostPosted: Mon May 12, 2008 11:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Also, I see it requires +5V Would I need a power supply with a dedicated +5V output or could I just link to +15V with an appropriate valued resistor?
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andrewF



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PostPosted: Mon May 12, 2008 4:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have three of these. They work fine as VCAs/shapers, perhaps not as refined as the new versions, but an excellent module to have.
I love the sounds from these..... tube warmth Wink

Virtually, any pentode tube will do the job. You will need a tube socket too.
There are many of these tubes around, that were used in old TVs or radios and are not especially sought after, so you can get a boxful off ebay for a few $$. different tubes will sound umm different, so it is worth trying a few.
A good place to check tube types is
http://tdsl.duncanamps.com/tubesearch.php
You want a 7 pin pentode.

The hard bit is many of these tubes require 300mA through the heater at (preferably 6.3V, though as low as 5V is okay in this case).
300mA is quite a lot of current in a modular - enough to drive 8 or so modules.
One easy solution is a 5V wallwart, just used to power the heater.
Else get a 1A 7805 regulator and build a separate little power supply. If you do this, it will be easy to bump it up to 6.3V by hanging two diodes off the ground pin.
If you have a strong PSU anyway, just put the 7805, with a couple of caps, heatsink and diodes, nearby, connected to the +V line.
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otherunicorn



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PostPosted: Mon May 12, 2008 5:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ha! I just wrote an answer that pretty much said all this, then hit the wrong button and lost it all! All I need add is that different pentodes may had different pin-outs. I've used 6AU6 and others. Also, look for one of the modern switchmode wall warts as used on mobile phones. You can probably pick up a 5 or 6 volt one for a dollar at a garage sale.
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andrewF



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PostPosted: Mon May 12, 2008 10:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Ken
most of what I wrote came from you originally anyway.

I asked much the same question a few years back Smile
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neandrewthal



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PostPosted: Tue May 13, 2008 10:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the replies. I'll be on the lookout for a suitable wall-wart.
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neandrewthal



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PostPosted: Sun Aug 10, 2008 12:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

andrewF wrote:
Else get a 1A 7805 regulator and build a separate little power supply. If you do this, it will be easy to bump it up to 6.3V by hanging two diodes off the ground pin.
If you have a strong PSU anyway, just put the 7805, with a couple of caps, heatsink and diodes, nearby, connected to the +V line.


I found this 15v - 5v stepdown circuit on the tellun site. It is in the lower right corner. Would this be suitable for this tube VCA? I'm not worried about 300ma as my power supply has 5A. Any tips on what heat sink to get, and how to hook it up? I've never used one before. I also don't understand the arrow that points up to 5v, when the 5v output is actually to the right Confused

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andrewF



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PostPosted: Sun Aug 10, 2008 5:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

It looks okay.
Don't worry about the 100 Ohm resistor just use the 5V output.
If you add two diodes in series between 7805 pin2 and ground, with both the diode's cathodes pointing to ground, the regulators output will be bumped up to approx 6.3V. It is not essential, but not hard to do either.

7805/pin2------ -->| ----- -->| ------- Ground

Regular diodes will do, very little current passes thru this connection.

Heatsink - reducing 15V to 5V at 300mA, it will get hot, lick your finger before you touch it! . Look at the heatsinks on Ken's site for his power supply PCB, something like that, bigger is better, should do the job.
If you clamp the 7805 directly to the heatsink without an insulator, the 7805 will be grounded and the diode mod above will not work

All this being said, a 5V wallwart is a much simpler solution and, if you find a used one for $1 or so, much cheaper.
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neandrewthal



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PostPosted: Sun Aug 10, 2008 9:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

andrewF wrote:

If you clamp the 7805 directly to the heatsink without an insulator, the 7805 will be grounded and the diode mod above will not work


What if I don't ground the heatsink? Looking at the CGS power supplies, as far as I can tell , the heatsinks are just connected to large isolated pads on the board.

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andrewF



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PostPosted: Sun Aug 10, 2008 10:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

In that case - no problem Smile
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