Power supply hum transmitted to loudspeakers

Thanks for your nice comments, Hal.  It's possible that the slight hum is related to the fact that my VAC Renaissance 70/70 MkIII amp is, I believe, a bit more than 15 years old.  Although VAC worked it over about three years ago, and replaced some capacitors among other things.  I'll mention also that the hum is apparently not the result of a ground loop, as I had done some experiments a while back to rule out that possibility.

Also, it seems that hum levels produced by this amp, and also its smaller brother the Renaissance 30/30, are particularly sensitive to heater-to-cathode leakage that may be present in its small signal tubes.  See this thread.  Although the tubes I'm presently using measure fine in that respect, on my Hickok 800A tube tester.   

In any event, it's safe to say that with speakers having more typical efficiencies of say 90 db the 10 inch distance at which the hum is audible would be substantially less.

Best regards,
-- Al
  

.. the faint buzz when your ears are within about 3 inches of the mid-range drivers or the tweeters is perfectly "normal".  

Back to the hum/woofer... I submit that at worst, you should hear a faint whisper of air when your ear is essentially right on top of the woofer and the amp is on. But a hum, at 10 inches?

I'm very much open to debate on this as in my opinion this simply should not be the case

@almarg
Thanks for that correction!

Al, even at 3 inches with your speakers I would not expect any buzz (maybe some hiss, but not buzz).

Nor hum at 10 inches.

One thing that can cause hum in amplifiers employing single-ended circuits is when the grid circuit of a tube is grounded independently of the cathode circuit. IME the two should use the same circuit (the same wire) to ground. In this way the differential effect of the grid and cathode circuits can prevent noise on the ground connection from being picked up. This is especially important if you run an AC heater circuit on the tubes!

Also, if you do have AC heaters, if the tubes show any leakage at all on the leakage test on a tube tester, they will introduce buzz. We've found that the Russian small signal triodes tend to have problems in this area, so if you are running EH, Sovtek or the like it might be a good idea to change them out and see if the problem is still there!

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.