Power supply hum transmitted to loudspeakers

Thanks very much, Ralph.

Other than the Sophia Electric 6SN7’s discussed in the thread that I linked to, which caused significant hum in my VAC 70/70 and in another member’s 30/30, the only small signal tubes I’ve used in the amp have been 1950’s/1960’s vintage tubes from various manufacturers. Currently two Sylvania 6SN7GTBs and two GE 6SN7GTBs. Some of those I’ve tried have had unmeasurable leakage, while all of the others (aside from the Sophia’s) had VERY minimal leakage. All of them (aside from the Sophia’s) produced similar amounts of hum/buzz. I don’t know if the amp uses AC or DC on the filaments of those tubes.

BTW, a few months after I posted in that other thread, shortly before the one-year warranty I purchased for the Sophia’s expired, I had them replaced under the warranty with a brand new quartet. The hum level with the replacements was ok for a few months, although a bit worse than with the vintage tubes. Eventually, though, their hum level degraded to the same level as with the first set, and their leakage measured poorly (it was not all that great even at the outset), so I retired them to my tube collection.

In any event, I’ve been very pleased with the sonics of the amp, and when VAC replaced various parts about 3 years ago (followed by a couple of days of burn-in and some listening tests) Kevin Hayes said that I should be good to go for about another 20 years. So I’ll leave well enough alone. BTW, the main reason I sent the amp to them was that one of its numerous power transformers shorted out. They wound up replacing all of the transformers (as well as some capacitors), I believe with ones they use in more recent models, because the original transformers were no longer available. They had to make some mechanical changes internally in order to accomplish that, but it worked out very nicely.

Thanks again. Best regards,
-- Al

This has evolved into a most informative discussion.  Ralph seems to indicate that buzz of any kind, even at 2-3 inches from tweeter/midrange should not be heard.  Can I take that to mean that an amplifier's noise floor should only express itself as hiss, if audible at all?  Any electrical buzz or hum at 3 inches should require investigation?  

Al, I do have a question for you.  I have both a VAC 300.1a and a Ren Sig 2A Preamplifier.  I have noticed no pertinent electrical buzz from either but both do have power transformer hum, not particularly disturbing, but noticeable in a very quiet room.  Kevin has suggested different stands that might not resonate but I am still unsure why potted transformers are quite so audible. (truly not disturbing while playing music through Kevin's most musical components)

@atmasphere 

Yes, I agree with you that my earlier comment - the faint buzz when your ears are within about 3 inches of the mid-range drivers or the tweeters is perfectly "normal" - is more accurately stated when buzz is replaced with hiss.

I consider any sound other than the music itself - no matter how labeled or categorized - to be part of the systems noise floor and undesirable, regardless of the distance ones ear is from the speaker. 

Most transformers hum - and most of it is because of dirty power.  A good way to eliminate this is using a balanced power isolation transformer, it is exceedingly efficient in eliminating hum. 

I use a power transformer similar to this one.

https://www.sweetwater.com/store/detail/P2400IT?adpos=1o1&creative=54989263441&device=c&...

Good Listening

Peter

Audiobrian 1-20-12017
Al, I do have a question for you. I have both a VAC 300.1a and a Ren Sig 2A Preamplifier. I have noticed no pertinent electrical buzz from either but both do have power transformer hum, not particularly disturbing, but noticeable in a very quiet room. Kevin has suggested different stands that might not resonate but I am still unsure why potted transformers are quite so audible. (truly not disturbing while playing music through Kevin’s most musical components)

I can’t really shed any light on that, Audiobrian. And my Renaissance 70/70 is of course a very different design than your 300.1a.  FWIW, though, my amp makes some very slight mechanical noises during the first 25 seconds or so after turn-on, at which point B+ is applied to the tubes, but it is subsequently totally silent in terms of mechanical noise.

The amp is placed atop a 4 inch Mapleshade Isolation Platform, which in turn rests on a set of Mapleshade Isoblocks.

Good comment by Peter, as always. In my case, I have reason to believe that I have better than average AC power quality.

Regards,
-- Al