power amp mechanical/output buzz

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band_master

Well-known member
Joined
Mar 14, 2011
Messages
68
hey guys,
I have a Hafler Transnova P3000 power amp that started acting up the other day. I powered it up and noticed a buzz/hum sound. It seems to be mechnical noise coming from the power transformer, but you can also hear it in the left channel speaker. The noise is especially noticeable when there is no input to the amp. I had some mechanical noise issues with a PSU for my mixing board that turned out to be the rectifiers, but would that explain the output buzz? Again, the mechanical noise seems to be coming directly from the power transformer.

http://www.hafler.com/techsupport/pdf/MAN1461C_P1500_P3000_man.pdf

cheers,
BD
 
First we have to rule out AC power line problems.  Can you take it to someone else's place in a different neighborhood and see if it buzzes there?
 
hmmm... (pun intented ;))

I am follwoing with iterest.
I have the same amp that does the mechanical hum, but the audio output is fine. I have tried mine in two different neighborhoods since I have recently moved(different town actually) and it's still mechanically humming. I have stopped using it because the hum is very annoying...

I am curious to see what suggestions one may offer.

 
Isn't power transformers where the noise comes? I'd try tightening the screws of it's lamination and if still noisy put some varnish to the winding.

JS
 
I haven't tried moving to a new A/C source, but the mechanical hum passes into the left channel audio only. this amp is dual channel so i am thinking it may be the bridge rectifier on the left side. the mechanical noise is very similar to the noise i had with my mixer PSU which was the rectifiers. i ordered parts to replace the rectifiers and the electrolytics. will advise.
 
well i replaced the two big 6800uf caps and the bridge rectifiers. still getting the buzz both mechanically and in the output stage. Wondering if one of the MOSFET transistors that is connected to the giant heat sink overheated. I did have the unit racked in a vertical position, which would have attracted heat to these components in the left channel, but with plenty of space around the unit. Interesting that the manual recommends adding fans to your rack above the power amp...what is the point then of having a power amp that does not require a noisy fan?!?!
 
so i replaced the mosfets in the left channel and...the mechanical buzz at the power transformer is dampened quite a bit, but it's still there. interestingly, the left speaker idles dead quiet, while the right speaker has a slight buzz now. i might go ahead and replace the right mosfets as well. each channel has a matched pair of Renesas 2SK1058 and match pair of 2SJ162. Since these are dual independent channels I didn't think I needed matched quads per mosfet. Am I wrong?
 

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