Getting rid of transformer hum

[Adam]

Mounting the transformer on a resonant steel chassis can clearly make things a lot worse - sometimes a housebrick on the amplifier's case can make the critical difference!

I think that I might just try that this weekend with my IPS-1. I'll use a weight plate instead of a brick, but same effect. If that gets rid of the hum, then I'll be a happy man.

 

[mgc]

I need related help on transformer hum

I have a McIntosh mc7106 amp. The main transformer began to hum, so I removed all the tar
and replaced it with a heat conductive epoxy that I placed under a vacuum to remove all the
air. This completely eliminated the hum. That was about 2 years ago. Just today (03/23/14)
it started to hum again. I hear no hum through the speakers, just the main power amp. Anybody
have ideas how to eliminate it, or what this might be an indication of?
Thanks.

 

[Speedskater]

Try it at someone else's house, it just might be an AC power problem.

 

[slipperybidness]

I have a McIntosh mc7106 amp. The main transformer began to hum, so I removed all the tar
and replaced it with a heat conductive epoxy that I placed under a vacuum to remove all the
air. This completely eliminated the hum. That was about 2 years ago. Just today (03/23/14)
it started to hum again. I hear no hum through the speakers, just the main power amp. Anybody
have ideas how to eliminate it, or what this might be an indication of?
Thanks.

Here's the thing about transformers: They hum.

Some are worse than others, but pretty much all of them have a mechanical hum, or will develop a mechanical hum eventually. If I can't hear it from the listening position, then I usually don't care about it.

I have not heard the Parasound Halo line, but I suspect that they may be onto something by encasing their transformers in epoxy to try to mitigate the mechanical hum.

 

[Ampdog]

The strange thing is that there is mechanical as well as electronic (circuit) hum. That does not happen often. Side question: Was this there all the time, or is it something that started at some time, i.o.w. is it a fault condition?

 

[Bryceo]

Some high temperature epoxy


Sent from my iPhone 5

 

[SoulPedal]

Fighting a similar Xformer hum on my McIntosh 2505. This was a long thread so can't say I read it all, but has anyone tried to "pull out the AC plug and reinsert 180 degrees" - just reverse the 2 prongs physically... of course assuming a 2 prong plug but I believe that was an old amp in the original question. This was an old trick used on Guitar amps that didn't have a ground prong to eliminate the 60Hz hum. My 2505 (built in the early 70's) also has 2 AC prongs.

My amp didn't used to hum until I started repairing it for the bad left channel. The Power Cap for that channel (9,300uF) was definitely leaking, so I found a cheap one to test it and ran about 6" of wire to it. -40V became stable. Then I replaced all output drivers (3 bad) with some lower quality product and now it all works but hums, speaker and X-former both, no inputs attached. Actually there was a noise at first from the boards (higher pitched) but now that's gone. And when I power it up with the speaker attached, it's a major BVVvvvvt! That can't be good.

So ordered correct parts direct from McIntosh today. $100 each cap (they're blue now, so can't just have one blue showing on top), and ordered their output transistors.

Question: Could my inferior temporary parts cause the hum? (hfe gain was double what it should be and max C-E voltage was 80V so at the rails of -40/+40.)

Oh, I did nothing to bias DC. I'm not sure how to do that, but I do have a scope and I should know this part of the process. I actually don't see anything adjustable on the driver boards. Where is this adjusted typically?

Thanks, kinda new to this so getting a big lesson on audio here. Maybe then I'll fix my Velodyne Sub amp next. Then I won't need my custom RS 4.5 install underneath the entertainment system. Maybe another thread eh? I have to share a pic then.

John

 

[KEW]

Fighting a similar Xformer hum on my McIntosh 2505. This was a long thread so can't say I read it all, but has anyone tried to "pull out the AC plug and reinsert 180 degrees" - just reverse the 2 prongs physically... of course assuming a 2 prong plug but I believe that was an old amp in the original question. This was an old trick used on Guitar amps that didn't have a ground prong to eliminate the 60Hz hum. My 2505 (built in the early 70's) also has 2 AC prongs.

John

That will often eliminate ground-loop hums, but I don't see how it would work on a transformer hum. Seems like you would still have the same forces at play regardless of the phase.

 

[Speedskater]

My first three questions about any humming amplifier:
Does it hum if?
1] the input cables are removed.
2] the inputs are shorted.
3] you take it to another building.

 

[David Broughton]

Hi,

I think it is definitely your transformer that was faulty.

I just bought a new Perreaux Audiant 80i integrated amplifier.

After returning home from the authorised dealer, I switched it on without connecting anything to the amp (no interconnects or speaker cable).

I immediately heard a distinct humming noise generated by the amp itself.

Called in the dealer; he immediately heard the humming noise, said it is a problem, and has taken it to be sent to the authorised repair persons. He suspects that it is the toroidal transformer on the amp that is faulty.

In fact, Perreaux indicated to me that very occasionally a toroidal transformer may not have been wound correctly or the varnish impregnation on the transformer was not done successfully.

Hard to believe on such a high end product, but alas all true.

The dealer plugged in a demo Audiant 80i at my house where my Audiant 80i was set up and plugged in. No hum at all on the demo!! So forget about AC and DC issues and ground loop problems. It had nothing to do with that!!!

Anyway, the dealer has given me the demo model to use in the meantime.

From a very disgruntled buyer.


David

 

[TLS Guy]

Hi,

I think it is definitely your transformer that was faulty.

I just bought a new Perreaux Audiant 80i integrated amplifier.

After returning home from the authorised dealer, I switched it on without connecting anything to the amp (no interconnects or speaker cable).

I immediately heard a distinct humming noise generated by the amp itself.

Called in the dealer; he immediately heard the humming noise, said it is a problem, and has taken it to be sent to the authorised repair persons. He suspects that it is the toroidal transformer on the amp that is faulty.

In fact, Perreaux indicated to me that very occasionally a toroidal transformer may not have been wound correctly or the varnish impregnation on the transformer was not done successfully.

Hard to believe on such a high end product, but alas all true.

The dealer plugged in a demo Audiant 80i at my house where my Audiant 80i was set up and plugged in. No hum at all on the demo!! So forget about AC and DC issues and ground loop problems. It had nothing to do with that!!!

Anyway, the dealer has given me the demo model to use in the meantime.

From a very disgruntled buyer.
David

You should be disgruntled.

Perreaux is an outfit I have had in my sights for sometime. Very rare for them to have transformer problems, eh?

Well in my view they shop in the cheapest markets for their components.

I have a good friend who had a lot of their gear for a few years. There was not a unit that did not end up on my workbench, some multiple times.

Here is his preamp showing a pretty cheap burnt out power transformer. Now a preamp does not take much power and to have a power transformer fail at anytime during the life of the unit is really in for a dig.

I refused to use an OEM replacement as the transformer did not meet by standards, even if it met theirs.

Here is a picture of their cheap burnt out transformer on top of the high quality unit I modified the unit to take.

Here is a picture of my mod.

Another real annoyance is that their potentiometers were sourced from the cheapest sources, and gave plenty of trouble.

They are not on my recommend list.

 

[David Broughton]

You will not believe it.

The demo Perreaux Audiant 80i packed up after I connected Apple TV to an optical input on the amp to stream music from my iPod. This is despite the fact that the Perreaux website indicates that you can play music wirelessly using Apple TV connected to the amp.

I then got a brand new Perreaux Audiant 80i amp which also has an audible hum even from the listening position. The dealer actually got two new Perreaux Audiant 80i's, and the second one also hums. Not as loud as the first Perreaux which I received, but nevertheless audible from a distance.

The dealer suspects that Perreaux must have got a bad batch of toroidal transformers which they are using on their Audiant 80i models.

Needless to say, I returned my third Perreaux and got a refund.

And the prices one pays to own a Perreaux... It is mind-boggling! Where is the quality control? Don't they hear humming when they individually test each new unit that is made? I think their prices in the circumstances amount to daylight robbery, even though the sound may be good.

Looking now for a different make amp which does not hum.

 

[TLS Guy]

You will not believe it.

The demo Perreaux Audiant 80i packed up after I connected Apple TV to an optical input on the amp to stream music from my iPod. This is despite the fact that the Perreaux website indicates that you can play music wirelessly using Apple TV connected to the amp.

I then got a brand new Perreaux Audiant 80i amp which also has an audible hum even from the listening position. The dealer actually got two new Perreaux Audiant 80i's, and the second one also hums. Not as loud as the first Perreaux which I received, but nevertheless audible from a distance.

The dealer suspects that Perreaux must have got a bad batch of toroidal transformers which they are using on their Audiant 80i models.

Needless to say, I returned my third Perreaux and got a refund.

And the prices one pays to own a Perreaux... It is mind-boggling! Where is the quality control? Don't they hear humming when they individually test each new unit that is made? I think their prices in the circumstances amount to daylight robbery, even though the sound may be good.

Looking now for a different make amp which does not hum.

Oh, I believe it alright and would expect it! You have learned a lesson the hard way.

 

[pradeepkumar]

Yeah! "You can increase the voltage rating on capacitors by connecting them in parallel"

 

[Speedskater]

Yeah! "You can increase the voltage rating on capacitors by connecting them in parallel"
..................................................

Connecting them in series, not in parallel. But there is a lot of fine print that goes with that connection. This is NOT permitted with capacitors connected to the AC power line.

 

[highfigh]

Connecting them in series, not in parallel. But there is a lot of fine print that goes with that connection. This is NOT permitted with capacitors connected to the AC power line.

Why would you connect caps on the AC line?

 

[highfigh]

Dear all,

I have a problem that I hope someone can help me with. I have a power amp that uses a toroidal transformer and is humming. Don't say it's because it doesn't know the words hence why the transformer hums The hum is definitely coming from the transformer as it is noticeable from the moment it is switched on and is also audible thru the speakers. I suspect it is due to one of two main problems:

2. The windings on the transformer may not be as fixed as it should be so it is causing minor movements that induces the hum.

I don't think there is a ground loop problem at all, although it is possible there is a small contribution the main problem is the transformer hum. As the power amp is old, I would not want to spend a lot of money to rectify this problem and ideally want to DIY a solution. I suppose I can dismantle the toroidal transformer and re-epoxy the windings to decrease any movement or even superglue each winding individually, is this likely to result in an improvement?

Secondly, does anyone know where or how I can DIY myself a DC filter for the incoming AC power line before it connects to the transformer? That way I figured it would eliminate the DC current before it gets anywhere near the toroidal transformer. What components do I need for this and how do I do this? Thanks in advance for any answers.........

WRT "1. There is a significant amount of DC in the power supply hence why it is humming."

WHAT????????????? Why would you have DC going to the power supply transformer or on the AC line?

I know this is an old thread, but it would be good if the OP sees these responses.

 

[Speedskater]

Why would you connect caps on the AC line?

"X" & "Y" type caps are connected to the AC line in filters.