Cant stop Aikido Humming

[toufu]

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]

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]

Hi!
Is the heater grounded?

 

[Brit01]

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]

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

 

[boywonder]

Here are a couple of threads that may be helpful:

http://www.diyaudio.com/forums/tubes-valves/139466-weird-fuzz-aikido-pre-help.html

Check out the posts around #274 in this thread:

http://www.diyaudio.com/forums/tubes-valves/126650-building-aikido-preamplifier-6.html#post1720762

 

[toufu]

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]

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]

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

 

[M Gregg]

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