Tube Power Supply Buzz

LL21

Well-Known Member
Dec 26, 2010
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Hi guys,

Technical question...when i turn on my Zanden DAC, there is a super-loud steady buzz that lasts about 60 seconds...and then it stops, and you can hear the signal...perfectly quiet, no hum, no noise.

This 'warm up buzz' is getting longer and longer...rectifier tube in the PSU? The buzz is super loud and gets louder or softer with preamp volume...but its is definitely the DAC because if i switch the preamp source...silent. If i flip the knob on the DAC to another setting...silence for a millisecond in between switching settings before buzz returns.

Rectifier tube going bad? Or might it be a choke filter? Thanks for any advice.
 

microstrip

VIP/Donor
May 30, 2010
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I will bet on the rectifier tube - may be the cathode emission is decreasing and limiting the current during the start on time, charging the capacitors much slower. The buzz can be caused by the ripple not being suppressed until voltage of the supply reaches the correct values. But I can be wrong - I will not bet a XLF on it! :)
 

DonH50

Member Sponsor & WBF Technical Expert
Jun 22, 2010
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The two things I have seen cause a buzz are rectifier tubes and in-rush current making the transformer (or choke) buzz until everything gets charged up. If it's the latter, which has often been the case for me, you can use your ears to listen around the amp and see if the transformer is buzzing at turn-on. If not, try swapping the rectifier tube as microstrip suggests.
 

LL21

Well-Known Member
Dec 26, 2010
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Bingo! I switched out the 2 Mullard 6CA4s in the PSU with 2 new Mullard 6CA4s...buzz instantly gone. I hope that solves it. Thanks to both Micro and Don.
 

LL21

Well-Known Member
Dec 26, 2010
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Micro - i am glad you did NOT bet an XLF on it...or that i did not offer to take you up on such a bet! ;)
 

LL21

Well-Known Member
Dec 26, 2010
14,411
2,509
1,448
No buzz this morning! Seems like it was just a rectifier tube...whew...
 

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