Power supply hum transmitted to loudspeakers

Normie, FWIW my speakers are rated at 98 db/1 watt/1 meter.  The gain of my amp isn't specified, nor is its sensitivity (gain can usually be calculated to a good approximation from the combination of sensitivity and maximum power capability specs), but I believe its gain is fairly high (in part because I am using the zero feedback setting of its feedback select switch).

I can hear a faint buzz when my ear is within about 3 inches of the mid-range drivers or the tweeters.  I can hear a faint hum when my ear is within about 10 inches of the woofers.

Ralph (Atmasphere), thanks for your characteristically informative post.  If I may offer a correction to a slight oversight in your arithmetic:

When designing an amplifier or preamp the challenge is that the end user might have a speaker of only 86 db (which is bordering on criminal IMO, due to the vast amount of power needed to make that work in most rooms, at least at the levels I like to play...), and at the other end of the spectrum is 107db. That's a range of 30db, which is 1000:1 in amplifier power (IOW, to do what an amp does on a speaker of 86 db, one need have 1/1000th the power to do it on a speaker of 106db)! Obviously this is a trick to make an amplifier of the same gain work on a range of speakers like that.

Should be:

When designing an amplifier or preamp the challenge is that the end user might have a speaker of only 86 db (which is bordering on criminal IMO, due to the vast amount of power needed to make that work in most rooms, at least at the levels I like to play...), and at the other end of the spectrum is 107db. That's a range of 21db, which is 126:1 in amplifier power (IOW, to do what an amp does on a speaker of 86 db, one need have 1/100th the power to do it on a speaker of 106db)! Obviously this is a trick to make an amplifier of the same gain work on a range of speakers like that.

Best regards,
-- Al
 

@almarg 

you already know I have the utmost respect for your "all things audio" knowledge, so I submit the following response to your last post with the utmost respect...

also, I am aware of your Daedalus Ulysses speakers and to my understanding they do not have their own built-in amp, which is relevant to my response....

assuming you have normal human hearing, I would argue you should NOT hear a faint hum when your ears are within about 10 inches of the woofers....

.. 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.

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