CMRR from parallel heaters? - diyAudio
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Old 18th March 2009, 09:07 AM   #1
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Default 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?
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Old 18th March 2009, 09:55 AM   #2
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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.

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Old 18th March 2009, 12:48 PM   #3
Gordy is offline Gordy  United Kingdom
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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.
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