Tranformer Hum?

[Dreadhead]

Hi,

I'm not a DIY builder but I have a balanced beta22

. The problem is that I have a serious case of tranformer hum. The system is in a single chassis and when the top cover is on there is audible hum on both channels. I'm thinking it's a magnetic issue because the hum is not audible when the cover is off though.

Also note The system has a ground loop breaker so I'd assume that this should get rid of any ground loop issues. Could this be being caused by DC in my AC circuit?

Any ideas? I only noticed this an hour or so ago and I've been seeing if anything is loose since.

Thanks,
Chris

 

[FallenAngel]

Generally, a lot of Beta22 amps with a transformer in the same case have transformer hum issues unless precautions are taken to prevent/remove it. I had a serious problem with transformer hum in my GainClone a few months back, try twisting the transformer, double check the ground wiring scheme and consider covering it in MuMetal. All of these combined (some more than others) remove my issue.

 

[Dreadhead]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Generally, a lot of Beta22 amps with a transformer in the same case have transformer hum issues unless precautions are taken to prevent/remove it. I had a serious problem with transformer hum in my GainClone a few months back, try twisting the transformer, double check the ground wiring scheme and consider covering it in MuMetal. All of these combined (some more than others) remove my issue.

Thanks for the quick reply.

Sorry to sound like an idiot but what do you mean by twisting the transformer? Rotating it (tried that to no effect) or turning it over?

Is it a worthwhile idea to try a large tin can before I go all the way to mu metal? That's not something I can just walk into a store and buy as far as I know.

Thanks again,
Chris

 

[el_matt0]

Hmm, seems bizarre that this wasnt something the builder of the amp took into consideration. There are pages and pages of discussion regarding this very major issue with the beta 22 over on head-wize. I believe n_maher was the one attempting many various means to solve the issue. Gist of it was, he tried a ton of different (and expensive) shielding materials, none of them worked that well I dont think. Not even lining a smaller chassis which "covered" the trafo within the larger b22 trafo helped fully. I dont believe that twisting the transformer would have any significant impact, as I've been told that the interference from a transformer should be visualized as a 3D sphere, and not just coming out the top and bottom - its been something I've asked and wondered also. Basically with most beta 22s, people are putting the transformers in separate chassis alltogether for the most part, either alone, or with the sigma22 boards as well. The few people that I've seen keep it in the same enclosure have only been with 3 board setups, and in all those cases, the transformer is located at the FURTHEST possible point in the chassis away from all of the signal paths. And in addition to that, they all incorporate some sort of wall/divider, usually shielded with Mu-metal or something of the sort. Its bizarre that at a MINIMUM that wasn't done in your amp, let alone the fact that its a balanced beta. FWIW I've yet to see a balanced beta22 with the trafo in the same case and no shielding - but I guess I just haven't been keeping my eyes open enough!

Best of luck resolving this, my guess is it might be tough to do if not impossible though unless you go through with relocating the transformer to a new case. I ran into a ton of buzz with my beta22 even with the transformer in its own case if the transformer chassis was even too "close" in proximity to the b22 chassis, it only disappeared alltogether with a distance of several feet between the two chassis.

 

[el_matt0]

And in response to your question, I'd be willing to bet almost any amount of money that a tin can would be totally useless, furthermore, so would mu-metal for the most part I think, the interference will find its way through holes and such, its not just a simple matter of throwing a sheet of something inbetween the transformer and the boards unfortunately.

 

[FallenAngel]

Yes, I do mean rotating it. Transformers emit EMI/RFI from some parts much more than others, so try rotating it by 15 degrees at a time to see which angle gives you the least amount of hum.

el_matt0 : Totally serious about rotating the transformer, this made the LARGEST difference in my search for a resolution.

It's also very important to check and double check the grounding on the amp. Photos might be warranted if you want another few pairs of eyes.

You can order MuMetal for VERY cheap from Electronic Goldmine. I don't know about a tin can, I'm no EE, just an enthusiast

 

[Dreadhead]

Well the builder is a head-fier actually (no names...) but I'm at least the 3rd person to own this amp.

Anyway it's not like it's audible during audio playback and actually with my HD650s it's entirely inaudible it's only my low impedance d5000s that give me problems. You have to sit in silence and concentrate even then. I'll give rotating a try again and be more careful. I did something when I did it because the buzz is gone from the right channel.

Thanks for the advice. I'll look into the mu metal if I don't have any luck. I've also got some dynamat I'll put under the transformer just in case it's a microphonics issue.

 

[vvs_75]

If the trafo sit in the corner you(we) can try to put it in the metal box just big enough to fit it in it. It could help.

 

[Dreadhead]

Well I flipped the transformer and put a candy tin over it and this reduced the hum a lot. I then lined the can with extreme dynamat and remounted the transformer on top of dynamat too. (needed a new mounting hole). Now I think it's still there but honestly I can't hear it

Thanks for the all the help.
Chris