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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
CGS 27 Tube VCA- noise
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hobgob_inc



Joined: Jun 09, 2009
Posts: 46
Location: Australia

PostPosted: Thu Dec 02, 2010 12:29 am    Post subject: CGS 27 Tube VCA- noise Reply with quote  Mark this post and the followings unread

Hey all,

Anyone who has built this have trouble with really loud hum?? I've been putting up with it for a while but thought I gotta sort it out. It's quite noticeable in recordings of quieter patches.

I'm using a 5V regulator mounted on the CGS27 board with diodes going to ground to boost the 5V, as per andrewF's great instruction a while back. Also have caps to decouple input and output of the reg. Apart from this its built as per Ken's instruction.

With nothing plugged into the module, the output is mostly quiet. As soon as I patch signal in it starts humming. Would this suggest a ground loop issue?? If so i cannot figure out why this may be. I love this module otherwise, its got a great sound for warming up patches and pretty much anything. I put my hammond thru it quite often as well.

Any help would be appreciated.


Cheers,
Luke
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Boogdish



Joined: Sep 21, 2009
Posts: 122
Location: Bloomington, IN

PostPosted: Sat Dec 04, 2010 11:22 am    Post subject: Reply with quote  Mark this post and the followings unread

I haven't built this module, but you could disconnect the sleeve connection on one end of one of your patch cords and use that to connect to the input to test if it really is a ground loop issue.
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hobgob_inc



Joined: Jun 09, 2009
Posts: 46
Location: Australia

PostPosted: Tue Dec 07, 2010 3:22 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah I have tried this. No sleeve on input and output still seems to have the same result for me. Thanks though.

Could it be anything to do with my crappy power supply? I reckon there would be a pretty heavy load on it.

Luke
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echoer



Joined: Dec 10, 2009
Posts: 40
Location: lawrence, ks

PostPosted: Fri Dec 17, 2010 11:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have built this module and have not had any issues with noise. The LEDs in the audio signal will impart a certain amount of noise in the circuit.

I don't know exactly how much current this module draws, but according to Kens module page "The tube chosen is the Russian sub-miniature 1J24B (1SH24B, 1Ж24Б). It operates on low voltage, and uses a mere 13ma at 1.2 volts for its heater." If the tube isn't pulling much current, the rest of the circuit certainly isn't.

I think you are on the right track with a ground issue. Check the PCB for a component not cleanly soldered to ground and double check the panel wiring. Touch/lightly wiggle all the parts and see if the sound gets worse or goes away.

If that doesn't work probably have a bad tube. I had a bad tube in one of my VCAs and I replacing it fixed the module. A faulty tube will definitely sound bad. The quality of these cheap Russian tubes leaves is questionable.
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hobgob_inc



Joined: Jun 09, 2009
Posts: 46
Location: Australia

PostPosted: Sat Dec 18, 2010 7:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

sorry double posted somehow. EDIT
Last edited by hobgob_inc on Sat Dec 18, 2010 7:40 pm; edited 1 time in total
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hobgob_inc



Joined: Jun 09, 2009
Posts: 46
Location: Australia

PostPosted: Sat Dec 18, 2010 7:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey thanks for the reply, but you are talking about the wrong module unfortunately. This is CGS 27, the tube experimenter not cgs 65 ( I think is the other one.) It draws a fair bit of current for the heater, about 300mA so i've heard. However the suggestions you have made I will definitely try out, probably just resolder all connections as there isn't many, and change the tube. I have one spare tube.

But in saying that it really doesn't sound like a bad tube to me, this is like a hum where bad tubes i've had in the past are more like a crackle and fizz sorta noise.

Anyone know if it could be to do with having a regulator on the board to supply the heater?

Thanks
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otherunicorn



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

PostPosted: Mon Dec 27, 2010 3:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Maybe you are introducing an earth loop, or maybe you have something that needs to be shielded. Maybe you are too near to a fluorescent lamp?
There should be no hum issues.

_________________
http://www.cgs.synth.net/
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PrimateSynthesis



Joined: May 02, 2008
Posts: 69
Location: U.S.A.

PostPosted: Thu Mar 17, 2011 5:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

hobgob_inc wrote:

Could it be anything to do with my crappy power supply? I reckon there would be a pretty heavy load on it.


Yes, a power supply that is over-loaded or lacks adequate filtering can cause hum. Have you tried adding a filter cap?
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