CMRR from parallel heaters?

dsavitsk · 18th March 2009, 09:07 AM

Does anyone know if one can supply noisy DC to each end of a heater with a grounded center tap (12au7, etc.) and obtain some level of common mode noise rejection? That is, can one use a DC supply that is noisier than one might use in this sort of arrangement?

Geek · 18th March 2009, 09:55 AM

That's what a traditional hum balance control does.

Hum is induced via h-k leakage. If both sides of the heater leak equally, they cancel each other out.

The CT sometimes works, but is rarely perfectly balanced to leakage currents.

Cheers!

Gordy · 18th March 2009, 12:48 PM

I do not know the actual answer, however I suggest that it would only work (in such as your 12au7 example) if the heaters were physically 100% anti-phase balanced within the unit. The few tubes that I have seen inside have clearly not had that structure, suggesting that you will simply get two dirty paths to ground, and most likely more noise.

18th March 2009, 09:07 AM	#1
dsavitsk diyAudio Member Join Date: Jan 2005 Location: Chicago	CMRR from parallel heaters? Does anyone know if one can supply noisy DC to each end of a heater with a grounded center tap (12au7, etc.) and obtain some level of common mode noise rejection? That is, can one use a DC supply that is noisier than one might use in this sort of arrangement? __________________ http://www.ecpaudio.com :: http://diy.ecpaudio.com

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18th March 2009, 09:55 AM	#2
Geek diyAudio Member Join Date: Sep 2004	That's what a traditional hum balance control does. Hum is induced via h-k leakage. If both sides of the heater leak equally, they cancel each other out. The CT sometimes works, but is rarely perfectly balanced to leakage currents. Cheers!

18th March 2009, 12:48 PM	#3
Gordy diyAudio Member Join Date: Nov 2006	I do not know the actual answer, however I suggest that it would only work (in such as your 12au7 example) if the heaters were physically 100% anti-phase balanced within the unit. The few tubes that I have seen inside have clearly not had that structure, suggesting that you will simply get two dirty paths to ground, and most likely more noise.