MOTM

I built two of the CGS65 VCA / Timbre Modulator. To quote Ken Stone:

The tube chosen is the Russian sub-miniature 1J24B (1SH24B, 1\u041624\u0411). It 
operates on low voltage, and uses a mere 13ma at 1.2 volts for its 
heater. In other words, the heater uses less power than the average LED.

For more information, post to the cgs_synth Yahoo group.

I plan soon to create sound samples from all of the more esoteric 
modules in my synth, including this VCA. I classify it as a Timbre 
Modulator. While it is also a VCA, it's tweaked towards distortion for 
input levels above about 2V p-p. As the level increases, a triangle wave 
input morphs into a type of pulse wave with quite pleasing harmonics. 
Using an envelope to make this dynamic produces musical results.

-Richard Brewster
http://www.pugix.com

Mark wrote:
> I'm very curious about the pentode VCA.  It looks like a very promising
> module for a number of reasons.
>
> http://www.cgs.synth.net/modules/cgs27_tube.html
>
> The parts are inexpensive and the design seems relatively simple.  In
> fact, I'm thinking it would take less time and money to build than an
> OTA-based design.  Perhaps more importantly, it only uses +15V for
> the plate voltage, so it does not require a separate power supply and
> it is relatively safe for DIY.
>
> The use of +15 plate voltages with pentodes also opens up the
> possibility of other voltage-controlled modules using tubes such as
> filters and waveshapers.
>
> How well does it work??  Do you have any examples how it sounds?
> While cut-off tubes are used in compressors, I was under the
> impression they didn't work well as gates. Did you have to bias the
> control voltage??  Did you connect the suppression grid to the
> cathode??
>
> Did you use a PCB from CGS??  There appears to be two, a CSG65 and a
> CSG27.   What did you use to supply the heater voltage??  I'm
> thinking a dual module using 6064 tubes would draw around 600mA,
> which would be about 75% of an MOTM-900. Then there is the other CGS
> tube VCA, that uses a tube that only draws 13mA:
>
> http://www.cgs.synth.net/modules/cgs65_vca.html
>
> Unfortunately, I am totally unfamiliar with the 1J24B /1J24B  and I
> cannot seem to find anything about it online written in English.
>
> I'm not familiar with directly-heated cathodes, so I'm a bit confused
> what pin 3 does, and the heater circuit shown in the CGS65 schematic.
> It also looks like the suppression grid is connected to the negative
> rail??
>
> Thanks for the update.  Your consideration is appreciated.
>
> On 3/4/07, Richard Brewster put forth:
>   
>> I got around to updating my website today.  I added the long promised
>> Wogglebug project page with full schematics and pictures, plus the three
>> latest modules:  Blacet StonZ Phaser, Oakley Superladder VCF, and CGS
>> Tube VCA / Timbre Modulator.  And a picture of the back of my CGS
>> Digital module, which has 8 circuit boards.  I took a new photo of the
>> MOTM-650, too.
>>
>> No, I'm not done, yet!  I am waiting for more MOTM to be announced.
>>
>> http://www.pugix.com
>>
>> Be sure to refresh your browser cache.
>>
>> -Richard Brewster
>>     
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