B&K monoblocks humming

audiocr381ve

I have a pair of B&K M200 monoblocks that have been sitting in the closet for awhile as I was on the hunt for a nice stereo rack (wife didn't want them on the floor, totally understandable). In the meantime I was using my trusty Parasound HCA-750a on a little table stand and was getting zero hum from my Totem Hawks. Well I found a rack and it was time to bring back the big monoblocks. They really do sound fantastic and smooth, but I'm getting some hum that's audible from several feet away. At my listening position, I can hear it if I try.

I'm not sure if there is a problem or not, but my guess is that these old amps just hum and that's that. If that's just the way it is, I'm not sure if I want to live with that. I'm just to OCD to have hum in my system.

OR

Do you think there is a problem? I have a guy in town who's supposedly a great tech who may be able to work on them.

Thanks gents

tonyb

Did ya try lifting the ground ? Try the easiest things first before trucking off to the repair shop. Btw- I'm also OCD when it comes to hums/buzzs/ground loops....I'd rip the whole thing apart to find it. Fortunately right now, mine is as quiet as a church mouse.

audiocr381ve

tonyb wrote: »

Did ya try lifting the ground ? Try the easiest things first before trucking off to the repair shop. Btw- I'm also OCD when it comes to hums/buzzs/ground loops....I'd rip the whole thing apart to find it. Fortunately right now, mine is as quiet as a church mouse.

I forget, do I lift the ground by using a cheat plug? I'm running the amps into an APC H15 power conditioner. I'm absolutely sure it's the amps since the Parasound didn't make any noise.

tonyb

Yeah...for the 2 bucks a plug, worth a shot.

audiocr381ve

tonyb wrote: »

Yeah...for the 2 bucks a plug, worth a shot.

Cool, will give it a shot. Thanks Tony

tonyb

I guess I should have asked prior to suggesting the cheater plugs....the hum is coming threw the speakers right ? It's not a hum from the amps themselves ?

audiocr381ve

tonyb wrote: »

I guess I should have asked prior to suggesting the cheater plugs....the hum is coming threw the speakers right ? It's not a hum from the amps themselves ?

Yep, through the speakers only.

tonyb

Good, then most likely a ground loop issue. Just wanted to make sure, hate to give out the wrong advice. Well, it is kinda entertaining for those on your bozo list but not guys I like.

F1nut

audiocr381ve wrote: »

I'm running the amps into an APC H15 power conditioner.

Don't do that, plug them straight into the outlet.

chumlie

f1nut wrote: »

don't do that, plug them straight into the outlet.

this !!!!

unc2701

Quick way to test for ground loop w/o having to go out & buy the cheater plug: grab a spare speaker wire and put it on bare metal on the chassis of the amp and bare metal on the chassis of the preamp. If the hum goes down/disappears as soon as they're connected, you've got ground loop.

unc2701

BTW, for completeness, transformer mechanical hum coming from the body of the amp (not through the speakers) is usually caused by DC on your AC line and can be solved by getting a PS Audio Humbuster or you can DIY one:
http://www.diyaudio.com/forums/solid-state/2080-dc-filter.html

Again, not the issue here, but good to know if you ever get the other kind of hum.

audiocr381ve

unc2701 wrote: »

Quick way to test for ground loop w/o having to go out & buy the cheater plug: grab a spare speaker wire and put it on bare metal on the chassis of the amp and bare metal on the chassis of the preamp. If the hum goes down/disappears as soon as they're connected, you've got ground loop.

Alrighty, the amps are plugged directly into the wall now. If this trick works, would it be a bad thing to keep the wire connected to both amp and pre?

unc2701

Not really- I had some Adcom 565's wired up like that for years. Think of it as treating the symptom instead of the disease.

Glen B

Mechanical hum audible across the room sounds like a DC problem. A ground loop will not cause mechanical noise. Emotiva makes a couple of filters that are claimed to eliminate hum from power line DC. I've custom built a few DC blockers.

Emotiva CMX-2 filter



Audiogon Thread - Transformer Hum

drumminman

unc2701 wrote: »

Quick way to test for ground loop w/o having to go out & buy the cheater plug: grab a spare speaker wire and put it on bare metal on the chassis of the amp and bare metal on the chassis of the preamp. If the hum goes down/disappears as soon as they're connected, you've got ground loop.

Or could be differing ground potentials between pieces of equipment (is that the same thing?). I had a terrible hum between coming out of my speakers in the two channel rig that nothing would solve: cheater plugs, unplugging cable and home theater, plugging amp directly into wall, etc. Once I connected the chassis of the linestage with that of the power amp, voila!, silence. All you can hear now is a faint tube hiss if you put your ear on the tweeter.

unc2701

drumminman wrote: »

Or could be differing ground potentials between pieces of equipment (is that the same thing?). I had a terrible hum between coming out of my speakers in the two channel rig that nothing would solve: cheater plugs, unplugging cable and home theater, plugging amp directly into wall, etc. Once I connected the chassis of the linestage with that of the power amp, voila!, silence. All you can hear now is a faint tube hiss if you put your ear on the tweeter.

Same thing as ground loop. Sometimes you do just get a hum no matter what and then the solution is to strap the chassis of the two.

BKphoto

unc2701 wrote: »

BTW, for completeness, transformer mechanical hum coming from the body of the amp (not through the speakers) is usually caused by DC on your AC line and can be solved by getting a PS Audio Humbuster or you can DIY one:
http://www.diyaudio.com/forums/solid-state/2080-dc-filter.html

I disagree, your transformer is old and dried out, starting to fail...

bthogan

BKphoto wrote: »

I disagree, your transformer is old and dried out, starting to fail...

What if the hum is intermittent, not constant, and not apparently related to load (i.e. music playing and/or volume)? Honest question. My amp's transformer hums now and then (there's no similar buzz or hum through speakers). The transformer is a relateively new Plitron. Other appliances also hum now and then (e.g. refrigerator). It sounds like it's DC on my AC, which would still be a drag (Humbuster isn't cheap), but a new transformer would be more of a hassle ($$$ plus sending amp in for installation).

Do you think transformer hum is generally a sign of old/failing transformer?

unc2701

bthogan wrote: »

Do you think transformer hum is generally a sign of old/failing transformer?

No. DC on your AC is the most likely cause of a hum from a toroidal transformer that's relatively new. I haven't used the $99 emotiva product that Glen links above, but DC blocking is relatively straightforward, so I wouldn't expect the PS Audio humbuster to outperform it.

I can't speak to BKphoto's experience, but with solid-state gear from the early 90's on, the times that I've encountered mechanical hum from the transformer, it's always been solved with a DC blocker.

bthogan

unc2701 wrote: »

No. DC on your AC is the most likely cause of a hum from a toroidal transformer that's relatively new. I haven't used the $99 emotiva product that Glen links above, but DC blocking is relatively straightforward, so I wouldn't expect the PS Audio humbuster to outperform it.

I can't speak to BKphoto's experience, but with solid-state gear from the early 90's on, the times that I've encountered mechanical hum from the transformer, it's always been solved with a DC blocker.

Actually, hadn't noticed that someone had linked to a $99 DC blocker - I just assumed folks were talking about the Humbuster (which I recall being around $300). Thanks for info.

btw my next audio-neurotic question is, does a DC blocker affect sound, like (e.g.) a line conditioner might? I haven't seen anyone saying it does, so I'll assume it doesn't unless someone says otherwise.

People seem to agree that the DC noise doesn't really harm the transformer - just causes hum. Is that correct? btw thanks for help.

BKphoto

No way you have DC on your AC line...I've seen many threads from people much smarter than me say thats impossible..

one that come to mind

..." I have never heard that one before. In fact it does not make much sense to me since DC has no frequency it would be completely silent.

Most buzzing transformers are caused by loose laminations. As the transformers age, due to the heat and constant vibration the varnish eventually breaks down and the transformer core (that is made from lots of thin plates stacked together) gets lose and starts to make noise. Sometimes this can also be caused by the input voltage or output current being too high and saturating the transformer core with excessive magnetic flux...."

by the way Amazon doesn't even carry the "Humbuster" anymore and i can only find it for sale in UK...

bthogan

BKphoto wrote: »

No way you have DC on your AC line...I've seen many threads from people much smarter than me say thats impossible..

one that come to mind

..." I have never heard that one before. In fact it does not make much sense to me since DC has no frequency it would be completely silent.

Most buzzing transformers are caused by loose laminations. As the transformers age, due to the heat and constant vibration the varnish eventually breaks down and the transformer core (that is made from lots of thin plates stacked together) gets lose and starts to make noise. Sometimes this can also be caused by the input voltage or output current being too high and saturating the transformer core with excessive magnetic flux...."

by the way Amazon doesn't even carry the "Humbuster" anymore and i can only find it for sale in UK...

That may be the problem - I won't pretend to fully understand the science of "DC on the AC", and I've come across credible sources that say that loose lamination can also be a cause of hum. On the other hand, I've also come across a lot of folks who say that Humbuster, or similar devices like the Emotiva thingie, got rid of hum. Doesn't seem subjective - there's a hum, or there isn't.

Also, I came across this device, which supposedly gets rid of hum that the Emotiva doesn't, and isn't much more expensive. I'm gonna give these folks a call tomorrow.

http://avahifi.com/index.php?option=com_content&view=article&id=270&Itemid=239

I'll try to remember to check in when I've got the device, and let y'all know if it works.

unc2701

I think the problem here is that BKphoto is thinking of EI transformers, and I believe that bthogan has a DNA-1 with an upgraded toroidal transformer. Delamination and airgaps are a cause of hum in EI transformers, but that isn't the situation here.


Please see the following, taken from Bryston's site; they down play the effects of DC on toroidal hum since they exclusively use toroidal transformers, but in the last paragraph, the recommend this EXACT solution:
http://bryston.com/PDF/newsletters/Bryston_Newsletter_V8_5.pdf

"DC Offset
All power transformers work with AC. DC (direct cur-
rent) cannot make the flux changes required to sustain
a transferable magnetic field. Under normal conditions
DC does not exist on power lines. However, because
of nasty things like cheap lighting dimmer switches,
sometimes a small DC component can occur on an
AC line. Because toroidal cores are so efficient, they
sustain magnetic flux easily. DC offset on an AC line
will eventually cause the toroidal core to go into satu-
ration by continually driving the core into one direction.
This sounds bad both literally and figuratively. But, it’s
rare and there are easy solutions. An EI transformer
core has unavoidable gaps. These gaps are generally
bad, both for stray magnetics and for overall efficiency.
But, they do help here in a passive way. An EI core
can’t sustain a magnetic field for long and any addi-
tional flux is sprayed out of its many gaps. So, in the
rare cases of DC offset, EIs can distribute the addi-
tional flux into surrounding circuits. Toroids can be
designed to take DC offset. This is usually only neces-
sary for extreme applications, like interruptible power
supplies.

Another option is to add a simple DC blocking circuit
on the primary side of the toroid. A few diodes and a
couple of capacitors easily handle the small amount of
DC that rarely gets onto AC lines. Many audio compa-
nies using toroidal transformers employ these simple
circuits to enjoy the overall benefits of toroids."

Bryston is known for obsessively eliminating noise in their products (to the point of hand rotating the transformers in every single amp to achieve the lowest possible noise and eliminating a single switch from a product because they found it added some noise), so I trust them over "threads from people much smarter than me".

BKphoto

"the small amount of
DC that rarely gets onto AC lines...."

this part stuck out the most...



have you turned on the amp with nothing at all attached...?

then take it to another part of the house and plug it in there...?

I'm probably wrong but I think this is a snake oil thing...


do you have any LED light bulbs in the room... I've heard that the cheaper brands add noise to the circuit...

bthogan

unc2701 wrote: »

I think the problem here is that BKphoto is thinking of EI transformers, and I believe that bthogan has a DNA-1 with an upgraded toroidal transformer. Delamination and airgaps are a cause of hum in EI transformers, but that isn't the situation here.

That sounds right; I do have a toroidal. I wasn't even aware that toroidals aren't succeptible to lamination issues - thanks for info. My previous reading made me think that this might be my problem, which would require a bit more than a Humdinger to rectify.

(In fact, a little more googling has informed me that lamination is among the primary characteristics that differentiate EIs from toroidals.)

doctorcilantro

Glen B wrote: »

Mechanical hum audible across the room sounds like a DC problem. A ground loop will not cause mechanical noise. Emotiva makes a couple of filters that are claimed to eliminate hum from power line DC. I've custom built a few DC blockers.

Emotiva CMX-2 filter



Audiogon Thread - Transformer Hum

Glen is right. Thought the CMX-2 is discontinued, you can ask Emotiva if they have any old stock left. AVA makes the Humdinger.

Glen - can your custom single output unit (as shown) be put in front of AC regenerators?

thanks!

User_227675

I have a pair of B&K M-200 monobloc's... They do not "humm" to much, only a very, very little on silence... Absolutely don't interfere with the music or be herd at normal listening and any volume!... They MUST be used with the quiescent current of output power transistor's in maximum regulated position, in order to work in class A for almost the double than origin!... And MUST be set on to pre-amplifier with balanced XLR connections!...

On this conditions, they are "warm", yes (and run really hot, it s normal) but the sound is NOT "mellow", but magnificent and beautly POWERFUL, with an absolute and complete CONTROL of bass and are capable of work with ALL types of loads!!

They are 150 AMPS each!... And power 200 W RMS into 8 ohms, 400 W RMS into 4 ohms and at could keep being used into even low than 1 ohms load with more than 800 W RMS!!!

For me this is the better quality price combination at the time (almost 25 years ago)... It work very well with the B&K MC-101 Sonata pre-amplifier - mine is the reference first one sending to Portugal by B&K staff for the importer analisys - but i notice that the XLR terminations are not in the comum position with others makers...

The B&K M-200's could even be upgraded in internal cables and MUST be used with a GOOD and proper main cable (i use Audioquest's).

My reference interconnect cables are the old's Deltec Black Slinks... With all this, the sound is a dynamic life event in every ways!

Glen B

doctorcilantro wrote: »

Glen is right. Thought the CMX-2 is discontinued, you can ask Emotiva if they have any old stock left. AVA makes the Humdinger.

Glen - can your custom single output unit (as shown) be put in front of AC regenerators?

thanks!

It can go anywhere you want. If the regenerator power transformer is humming, it makes sense to have DC blocking ahead of the unit. I completed one a couple of weeks ago for Audiogon member "Grimace" who wanted a 20A duplex. He is very happy with it (post #32): http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1333477504&openflup&32&4#32