Cant stop Aikido Humming

toufu · 11th August 2010, 03:55 AM

I just finished the Aikido preamp. And I can't stop it from loud humming. The hum seems to come from the volume pot to the input on the board. When the volume pot is closed, there is no noise, but as soon as I open the pot, I get a real loud humming. Any solutions? This thing is driving me crazy, I replaced the pot with just a couple of 75k resistors and it is still humming.

Globulator · 11th August 2010, 07:08 AM

Sounds like the hum source is in front of the volume control then.
The control itself is passive and cannot hum.

If there is nothing obvious I'd check the (signal) grounding path, that should lead from the input to the output - stage by stage - without touching the chassis etc.

azazello · 11th August 2010, 08:37 AM

Hi!
Is the heater grounded?

Brit01 · 11th August 2010, 11:27 AM

Do you have a shielded cable from the pot to the board and is it grounded well at one end only?

Does it hum louder if you place your finger near the cable?

richwalters · 11th August 2010, 02:23 PM

Input stage grounding issues: where is the heater wiring connected to the chassis ?
rough layout would be helpful.

boywonder · 11th August 2010, 11:37 PM

Here are a couple of threads that may be helpful:

Weird fuzz from Aikido Pre, HELP!

Check out the posts around #274 in this thread:

Building a Aikido preamplifier

toufu · 26th August 2010, 04:15 PM

Thanks guys, I did a few things, I connected the shield from ECC88 to the ground, added 20R to the chassis ground and added 360K resistors across the output RCA's and the noise is reduced considerably. Does that seem right? Or are there other things I can try as well? Thanks again,

M Gregg · 08:38 PM

Toufu,

Do you have coupling capacitors on the input to the tubes? I have had pick up on these when the volume is turned up! I cured this by wrapping foil around the caps and connecting a drain wire from the foil to ground! You must insulate the foil from any power on the amp! Its something you could try!

Regards
M. Gregg

aardvarkash10 · 26th August 2010, 09:02 PM

anti-parallel diodes on the signal ground/chassis ground connection. Beats a resistor by an order of magnitude!

M Gregg · 26th August 2010, 09:05 PM

Have you tried disconnecting one of the input connections to see if you have a ground loop? If the hum stops then its because you have ground connected on both ends of your input leads! Thats another thing you could try!

Regards
M. Gregg

11th August 2010, 03:55 AM	#1
toufu diyAudio Member Join Date: Jun 2008 Location: San Francisco	Cant stop Aikido Humming I just finished the Aikido preamp. And I can't stop it from loud humming. The hum seems to come from the volume pot to the input on the board. When the volume pot is closed, there is no noise, but as soon as I open the pot, I get a real loud humming. Any solutions? This thing is driving me crazy, I replaced the pot with just a couple of 75k resistors and it is still humming.

26th August 2010, 08:35 PM	#8
M Gregg diyAudio Member Join Date: Jun 2010 Location: UK	Toufu, Do you have coupling capacitors on the input to the tubes? I have had pick up on these when the volume is turned up! I cured this by wrapping foil around the caps and connecting a drain wire from the foil to ground! You must insulate the foil from any power on the amp! Its something you could try! Regards M. Gregg Last edited by M Gregg; 26th August 2010 at 08:38 PM.

26th August 2010, 09:02 PM	#9
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	anti-parallel diodes on the signal ground/chassis ground connection. Beats a resistor by an order of magnitude! __________________ Yes, conservatism thrives on low intelligence and poor information. But the liberals in politics... continue to back off, yielding to the supremacy of the stupid. It's turkeys all the way down. - George Monbiot, guardian.co.uk, 6 Feb 2012

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11th August 2010, 07:08 AM	#2
Globulator diyAudio Member Join Date: Aug 2004 Location: Cambridge, England.	Sounds like the hum source is in front of the volume control then. The control itself is passive and cannot hum. If there is nothing obvious I'd check the (signal) grounding path, that should lead from the input to the output - stage by stage - without touching the chassis etc.

11th August 2010, 08:37 AM	#3
azazello diyAudio Member Join Date: Aug 2008 Location: Bulgaria	Hi! Is the heater grounded?

11th August 2010, 11:27 AM	#4
Brit01 diyAudio Member Join Date: Jul 2008	Do you have a shielded cable from the pot to the board and is it grounded well at one end only? Does it hum louder if you place your finger near the cable?

11th August 2010, 02:23 PM	#5
richwalters diyAudio Member Join Date: Sep 2003 Location: Alps:Tube amp designs over 150W, SMPS guru.	Input stage grounding issues: where is the heater wiring connected to the chassis ? rough layout would be helpful.

11th August 2010, 11:37 PM	#6
boywonder diyAudio Member Join Date: Jan 2008 Location: So.Cal.	Here are a couple of threads that may be helpful: Weird fuzz from Aikido Pre, HELP! Check out the posts around #274 in this thread: Building a Aikido preamplifier

26th August 2010, 04:15 PM	#7
toufu diyAudio Member Join Date: Jun 2008 Location: San Francisco	Thanks guys, I did a few things, I connected the shield from ECC88 to the ground, added 20R to the chassis ground and added 360K resistors across the output RCA's and the noise is reduced considerably. Does that seem right? Or are there other things I can try as well? Thanks again,

26th August 2010, 09:05 PM	#10
M Gregg diyAudio Member Join Date: Jun 2010 Location: UK	Have you tried disconnecting one of the input connections to see if you have a ground loop? If the hum stops then its because you have ground connected on both ends of your input leads! Thats another thing you could try! Regards M. Gregg

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