transformer hum....is it normal???

[eddog]

I have completed a 3886 amp and it sounds great and voltages all are good. However I am hearing a low hum,not in the speakers, but at the transformers. These are EL types that were buyouts at PE. I am using 4 of them. Is this a sign of a problem or is this to be expeted from cheap transformers?

 

[lndm]

If it is what I'm thinking, I have experienced this too, and believe it is common. The laminations are singing with the mains frequency due to them buckling with the magnetism they carry.

The problem, apart from the noise, is a slight loss of efficiency which will turn to heat in the laminations. If you leave your unit on for a while, then turn it off and put your hand onto the laminations, and can keep it there then I think you should be OK with this.

The fix could be to tighten the bolts if any. If this doesn't help you could enclose the xfmr in a suitable case (with enough breathing room), or use another xfmr.

 

[eddog]

Thanks for the explaination! I can put my hands on the transformers after it has played for a hour, but there is quite a bit of heat radiating off them. At rest the units(all four together in parallel)draw about 1/2 amp from the variable power supply I am using to test with. I'll play it safe and fuse it at 2 amps and run it for longer periods of time and check it out. Thanks for your help.

 

[Bazukaz]

I think you could try to immerse trafo in nitro varnish and dry it out well.
This may help.

Regards,
Lukas.

 

[eddog]

Thanks for the advice, however I have decided to wire the tranny's differently and this has stopped the buzzing problem. Instead of the 4 traffo's wired all parallel to the supply I have wired them as 2 in series in parallel with the other 2 trafo's. This brings my operating voltage down to around 20 volts DC per side instead of the nearly 40vdc I had before. That's OK with me though as it gives me more room for lower ohm loads. Thanks for your help folks, i always learn something new here when I ask a question!

Thanks
Mark