Transformer Hum (I think)

[JoshT289]

As I posted before, I recently purchased a used Premier 11A and soon after sent it into CJ for them to diagnose the cause of repeated blown fuses. It turned out that the cause was just a bad power tube and Jeff told me that the amp was a "9 out of 10" and clearly well cared for, and asked me if I'd be interested in the C1 Teflon Cap upgrade. I agreed and the work was done promptly and I got the amp back a few weeks ago. It sounds absolutely amazing - in fact it sounded great to me out of the box, and has only improved since. I'd say I definitely have over 200 hours on it by now but probably under 300.

But that's all background and update information. Unfortunately, I do now hear a hum coming from the amp that I would describe as higher in pitch than 60hz. It is clearly audible when I am next to the amp, but I cannot hear it at all once I am about three to four feet away, and my wife cannot hear it from the listening position. Even up close it is quiet enough that you cannot hear it over even low volume music. I wouldn't even bring this up, but the amp was dead silent when I first bought it and when I sent it into CJ.

I can confirm that there is no hum through the speakers whatsoever, which initially is what I had assumed when I heard it. (There's not even any audible tube noise - through the speakers it is dead silent.) The only sound is coming from the amp itself.

So I am wondering what could have changed. Can transformers get louder with the change in capacitors? CJ gave it such a high mark in condition, which I made sure to confirm before agreeing to put the money in for the capacitors, and I trust CJ (Jeff).

I'd welcome any suggestions on what might resolve the issue. I have not yet reached out to CJ, partly because I initially figured I was hearing a ground loop that I could address, but I might call to pick Jeff's brains a bit. I just hope it doesn't get worse over time.

[AnotherJohnson]

My LP275Ms hummed a bit when they were on a second story wood floor. Back on ground level concrete, no hum.

I talked with CJ about this, and they suggested transformer insulation failure, although you say your hum is above 60 Hz, which seems odd. Lucky for me, it turned out the transformer insulation is fine.

Can you change the hum by pressing on anything? Are all the fixing screws tight?

[JoshT289]

Thanks AJ.

It might be 60hz - but I might be hearing a sympathetic resonance that goes higher? I just listened again, and it seems like there is a 60hz hum but with a higher tone overlaying it. But my wife says she only hears a single tone and her hearing is better than mine.

I'll try the fixing screws - just pushing down on each of the three transformers didn't do anything, but I might not have been pushing hard enough (don't have a lot of upper body strength.

I hope it's not insulation failure as I'd think they'd check for that when I sent the amp in and asked for a check up.

Thanks again. I'll keep pondering and prodding, lol.

[AnotherJohnson]

I hope it's not insulation failure as I'd think they'd check for that when I sent the amp in and asked for a check up.

I’m sure it’s not.

You can drive yourself nuts.

Do make sure all screws are “snug tight,” but don’t go overboard.

Make sure the foundation isn’t sympathetically exacerbating the vibration.

If you can’t hear it from the listener’s seat, forget about it.

[AnotherJohnson]

JF said (when trouble shooting my issue) that my amps were compatible with new transformers CJ was using in a current model. He said he would be making another order soon, and if I wanted to R&R my transformers, I should just let him know.

Instead, I moved the LP275Ms back to their original system, and they were perfect there, as they’d been before.

There were two problems that created my hum. First, the second story wood floor was not as flex free as the first story concrete floor. Second, the first floor room was on its own hvac zone, so the amp was cooled by the AC more effectively. The hum only showed up in the second floor system after an hour of heating up. The second floor system was part of a larger hvac zone, so the amp was not the main focus of the AC.

[roberto]

Hola. Hum is coming from the main power transformer. There are three transformers. Two are identical.
First put two quarter coins on each rubber foot of the amp. This is for brake the mechanical impedance between the amp feet and the wood base.
Other is with the help of two wooden pine lugs size 3 X 2 X 15 inches, rest the chassis of the amp, left and right side in a such manner that the wood is touching the chassis only, not the rubber feet. It is important to use pine wood only. This tweak costs nothing and really brakes the simpathetic resonance.
Try it, you might get lucky as I was.

Happy listening!

[JoshT289]

Thanks guys! I'll play around and try your suggestions.

I'm also not going to let it bug me too much even if it persists though, which is probably the best advice!

[admin]

If the hum was truly 60 hz, it may be a ground loop. This would also explain why when you moved it to a new system it went away. I've had ground loop issues in my system previously.

Get an RCA to RCA ground loop isolator (they are cheap), and it will tell you whether it's a ground loop or not.

Example: https://www.amazon.com/InstallGear-Grou ... NrPXRydWU=

[AnotherJohnson]

If the hum was truly 60 hz, it may be a ground loop. This would also explain why when you moved it to a new system it went away. I've had ground loop issues in my system previously.

Get an RCA to RCA ground loop isolator (they are cheap), and it will tell you whether it's a ground loop or not.

Mechanical vibration that only appears in the structure and not in the electrical audio path is never a ground loop.

[admin]

Very correct AJ. I just reread the original post, I misread it as hum coming from the speaker when Josh clearly states it is not. Definitely not a ground loop.

[roberto]

In my experience, sometimes the feet get to hard during ageing, and the vibration of the transformer is transfer to the wood furniture. I manage to isolate that problem long time ago with my Premier Four. That's what I did. Using two coins and later on, with the pine lugs. I did try a lot of different kind of woods and the pine really absorbs the unwanted vibration, just my 2 cents,

Happy listening!

[AnotherJohnson]

In my experience, sometimes the feet get to hard during ageing, and the vibration of the transformer is transfer to the wood furniture. I manage to isolate that problem long time ago with my Premier Four. That's what I did. Using two coins and later on, with the pine lugs. I did try a lot of different kind of woods and the pine really absorbs the unwanted vibration, just my 2 cents,

Happy listening!

It could have even been a leveling issue. The support resonances are a big factor in the sound generated by mechanical vibrations. Sometimes just picking up the unit and setting it down differently can temporarily help.

Your coins and pine boards changed the mechanical impedance and so altered the mechanical energy flow from the amp to the floor (or table).

One thing is sure. If energy is going into a sympathetic flat surface, like table top or floor, it will couple with the air and you will hear it.

The closer the vibration is to the coincidence frequency (at which the speed of sound in the flat panel matches the speed of sound in the surrounding air), the louder the acoustic manifestation of the mechanical vibration will be in the room

[AnotherJohnson]

FWIW, on guitar combo amps, the amp chassis is fastened upside down to the underside of the top of the cabinet.

In my experience, and I’ve owned and sorted out many a tube amp, if I hear any 60 hz buzzing, I whip out the #2 Phillip’s head and look for the loose chassis to cabinet fixing screw. Often there will be two or three that need a twist. 99% of the time, that’s all that’s needed if the amp is a modern unit (say a 2005 Rivera compared to a 1965 Fender).

Old guitar amps generally need recapping. Just like old audio amps. Old electrolytic filter caps don’t block 60 hz as well as they did when new.

[roberto]

Yes AJ,

The good thing is that I could lower the quantity of intensity of the 60Hz hum and upper harmonics with this tweak up to a point where only placing your ears very close to the transformer you could hear it. The vibration of the 60Hz from the transformer is resonating with the furniture wood and changing it's resonance or taming, reducing, cutting down this resonance with these two methods worked. It is a simple thing to do, and cost nothing.

Josh, just give it a try and see what happens, you might get lucky as I did. Remember to use different size of coins and try. Reducing the size, as an example first coin in the foot, the 50 cent s, the the quarter. Also you could use spikes. The clue is diminishing the contact area with the furniture might reduce this unwanted hum. Also you could try different materials like rubber or similar material.

Happy listening!

[JoshT289]

Hi Guys,

Thanks for the ongoing discussion! Here is an update that I am generally very happy with:

Upon a closer listen, I realized that most of what I was hearing was coming from my left subwoofer, which is rather near the 11A. When I turned that subwoofer off, the remaining audible hum was quieter and more of a higher frequency. So, I tightened the screws on top of the transformer covers and on the top of the amp surface. Sure enough a few of the screws were a bit loose and now they are all snug (but I didn't over torque at all). The result is almost total silence from the amp now, and certainly as quiet as it had been before I sent it to CJ for the cap upgrade. My wife and brother can still hear what they call a "very slight hum" with their ears right above the amp - I cannot at all.

So, now I need to address that subwoofer hum, lol, but that doesn't worry me. I assume it's a loose connection or perhaps the cable is crossed or too close to an interconnect on the left channel. Anyway, I've dealt with and resolved those before.

Thanks again for keeping me motivated without freaking me out, LOL. Everything seems rosy with the amp now.

With much thanks,

Your friend,

Josh

[AnotherJohnson]

That’s great!

You may have mentioned the subwoofer model and age. I don’t remember.

But … as you point out, it could be a ground or interference issue with the feed. But if it’s an older unit, and if it’s a buzz or rattle rather than a hum, it could be that some loose screws or possibly failed adhesive fixing the cone, or the crossover.

It isn’t hard to renew adhesive or tighten screws and it may be all you need to totally dispatch the unwanted noise.

[roberto]

That changes everything Josh,

It is not coming from the amplifier, the hum is coming from the sub.
The first thing to do is, disconnect the input from the sub and have a hum listening. If the hum is gone, or the RCA cable is contaminated or it is coming from the receiver or preamp where it is connected. Usually this problem is a ground loop. Disconnect the tv signal cable from the the tv box, if there is no hum, them you need a 1:1 tv noise cancelling transformer.
The members will come with more thoughts about how to cut that noise problem.
Please tell us more about it...we might can help you regarding of how to get rid off the unwanted hum.

Happy listening!

[Tommd]

in my situation the hum eventually turned out to be due to power supply capacitors that had had their day. After I had them replaced (by heavier ones) it didn't suddenly sound better and tighter, but the hum had also completely disappeared. You can simply measure the value; if the capacity has dropped below 70% replace them.. A real win win situation..

[AnotherJohnson]

in my situation the hum eventually turned out to be due to power supply capacitors that had had their day. After I had them replaced (by heavier ones) it didn't suddenly sound better and tighter, but the hum had also completely disappeared. You can simply measure the value; if the capacity has dropped below 70% replace them.. A real win win situation..

Power supply filter caps are supposed to take the ripple (hum) out, so in an older unit, it is always a good place to look for hum if simple ground loops have been ruled out.