Power supply hum transmitted to loudspeakers

As relates to the transformer hum from my VAC amplifier and preamplifier power supply, I have them both plugged into a Torus 20A RM-20 isolation transformer based power conditioner. I believe isolation transformers are just as effective in eliminating hum inducing DC as humbusters. No change plugged directly into dedicated 20A outlets.  I'll try some sorbothane under the components to see if it help....they sure sound great playing music when I don't notice the mechanical transformer hum.

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

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

@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. 

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)

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

.. 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 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
  

@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.

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
 

@normie57, it could be the quality of the AC coming into your home from the grid. Even though you have a dedicated line from your circuit box, it is not completely isolated from noise. 

With your fine OTLs and the sensitive loudspeakers you often use, can you hear any noise/hiss 1-2 ft from your loudspeakers at idle? My VAC amps and my AudioNote Kit Interstage Monoblocks both have low level buzz audible 1 ft from my KEF Ref 3's, not particularly sensitive loudspeakers.

I need to nail down some variables here. The speakers I have at home are 98 db; at shows they are either 98 or 107 db.

With 98 db I have to have my head by the mouth of the mid-range horn to hear anything. What I hear is a gentle hiss. With the 107 db speakers the hiss is more apparent- so we developed a little 'jumper plug' that replaces a tube in the voltage amplifier of our amps. With the plug installed where the tube was we knock out about 12 db of gain and then the hiss is back down to an acceptable level.

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.

For this reason amp manufacturers tend to make amps of more or less gain depending on the speaker that might be used with their amps, which has a lot to do with how much power the amp can make. If a really high powered amp (+500 watts) the gain is going to be 30-36 db (there are some outliers; the Hurricane amp has 50db!); for a really low power amp that will only see use on speakers of +100db, the gain might be only 12-15 db. We typically set our gain around 25db, which is fairly reasonable to work on speakers from about 87db up to about 101db or so.

Keep in mind that on a really high efficiency speaker, its unlikely that you won't hear some sort of hiss or buzz coming from the electronics. It can get to be a bit of a challenge to design for speakers like that, even if your amp is only making a few watts.

So to answer your question with all that in mind, it sounds like you have a problem somewhere- with KEFs I would expect that you would have to lay your ear directly on the tweeter before you could hear any noise floor at all.

I can put my ear up to the tweeters in my rig and it's dead quiet, unless music is playing and then it's painful…so don't do that second thing…but try a Humbuster if you can find one. I do tolerate some hum from guitar amps, especially a single ended Class A Burriss Royal Bluesman head I use that has some hum that seems to emanate from my pedalboard…frustrating but worth it as the amp is so good.

I'd like to share an observation.  Two days ago I moved my audio system to a really silent room that my stepson vacated. The room is extremely quiet but the components are closer as are the loudspeakers.
 Now that background noise has been virtually eliminated I can say that my two amplifiers that I thought were dead silent have minor transformer hum and there is a very minor buzz from my loudspeakers. Perhaps Brian is correct, above, concluding all components have very minor electrical or mechanical noise which should be ignored if not audible from the listening position.  

A question for Atmashere/Ralph:(and others who care to contribute)

With your fine OTLs and the sensitive loudspeakers you often use, can you hear any noise/hiss 1-2 ft from your loudspeakers at idle? My VAC amps and my AudioNote Kit Interstage Monoblocks both have low level buzz audible 1 ft from my KEF Ref 3's, not particularly sensitive loudspeakers. This occurs when they are plugged directly into dedicated outlets or my Torus isolation transformer. Thanks!

I guess a good question is how much noise emanating from your loudspeaker, once your system is energized, is normal? I avoid saying acceptable as we all have different tolerances.  When we place our ears 12 inches from the tweeter or midrange driver and hear a low level, buzz, hum or hiss, with nothing audible at the listening chair, is this normal/expected? When I run tube gear I often hear a low level hiss, with solid state a low level buzz, but no more than 1-2 ft from the loudspeakers. 

I had some transformer hum from a high current SS amp I use for a spare speaker system (for my deck) and a PS Audio Humbuster III completely fixed the issue. I now plug both of my amps into it although my main tube amp is quiet anyway. I demand that my system is humless and it is…I have lighting dimmers here and there and they don't bother the rig, and even my turntable is dead quiet after I put a new din plug Mogami cable on the Akito arm (Jelco or something). P.S. Audio should have kept making the humbusters…they're cool.

@boxer12 i disagree about shielded power 'chords' being an absolute must.
i thought the same when i made my first batch of power cords and made them all shielded. they did, indeed, make my system quieter. after further builds with different architectures and materials, i have found that unshielded power cords can be just as quiet as shielded and can sound less compressed.  as usual, it all depends on the system.. the one caveat is that pretty much everyone agrees that digital components do best with shielded PCs.

have had their power supply upgraded, but still has a small amount of buzz at the loudspeakers, not audible while playing music beautifully.(with and without shorting plugs). I've learned to ignore it and realize the amplifier was meant to play music, not to necessarily be dead silent at idle.

Its worth getting to the bottom of little buzzes like this- you will notice the system sounding better. The reason is, depending on how the buzz originates, it can cause intermodulations. Its worth it to get them gone!

Thanks for all your thoughtful responses.
I realize that this discussion has as much to do with psychology as electronics.  What's easy for some to ignore or even sound soothing, drives others crazy...as Mr Spock used to say 'fascinating'. 
As I really enjoy the amplifiers I will try to ignore the idle buzz, barely audible from listening chair, and enjoy the music. I have read for years that idle noise rides on the music, which has led me to believe my enjoyment might be improved by eliminating it. I'm gonna discard that notion, realizing it might be true, and just put on another record or CD asap so I don't hear the buzz at idle.  I don't want to sell the amps just to replace it with one that's dead silent and perhaps not as musically satisfying!  Enjoy and thanks!

I believe most amplifiers/systems have some very minimal noise audible through the loudspeakers at idle. Some have background AC, ceiling fans, pool pumps etc which make this noise floor less or perceptibly inaudible.  I own some Clayton monoblocks which I love, have had their power supply upgraded, but still has a small amount of buzz at the loudspeakers, not audible while playing music beautifully.(with and without shorting plugs). I've learned to ignore it and realize the amplifier was meant to play music, not to necessarily be dead silent at idle.
Good luck!

I run high efficiency Lowther speakers. They pick up everything. FWIW... What has helped my system is running everything except the mono amps through an Exact Power SP15 transformer. Also, I've found that I need to keep the SUT away from the other electronics. Well shielded  interconnects & power chords are also a must. 

I agree with Cleeds. To make a meaningful test of an amplifier's intrinsic noise level shorting plugs should be connected to its inputs.

Many choices of RCA shorting plugs can be found at eBay, by entering "RCA shorting plugs" into its search box.

Regards,
-- Al

@normie57

if its a "hum", try this https://emotiva.com/products/accessories/cmx-2

Hi Normie,

Noise is a problem with all active devices. It's caused by several things, but what can make it audible is high gain in the system, along with high efficiency speakers.

For some reason traditionally preamps are made with WAY too much gain. PrimaLuna is one of the few makers who make preamps with more reasonable gain amounts, therefore lowering the total noise.

As others have pointed out, what's really important is your peception of it. My system is reasonably quiet, but in the middle of a wind storm or with the heater blowing, it's the least of my problems. :)

E

normie57

... Is it not almost universal that all amplifiers with power transformers have some low level power supply noise that will cause minimal leakage hum, buzz, or hiss through the loudspeaker with your ear close enough and no inputs to the amp connected?

If you want to test an amplifier, doing so with no inputs connected really doesn't tell you anything. That's not how the amplifier was designed to be used.

If you can hear it and its disturbing, it can't be ignored.  I had to shut up a whispering attendee at a concert the other night.  My amp is DEAD quiet.