2. amps-preamps
  3. 1177011842

Need Help Combating Power Amp hum

I have a vintage Forte Model 5 power amp purchased used on Audiogon. It is a nice sounding amp, but is plagued with a constant, low level HUMMM which is just audible from my listening chair when the room is very quiet. I understand hum modulates/distorts the music which is undesirable.
My speakers are an MTM design with 90dB sensitivity (the other owner used Magnapans and didn't notice the hum).

The amp uses a toroidal power transformer and all the signal wires are routed carefully away from the power supply components. The hum occurs even when the inputs are shorted/disconnected, ruling out my other components. Power cord polarity and grounding were also checked.

Any ideas/techchniques to eliminate this hum?
chasmo

Showing 1 response by jitterbug

jitterbug
15 posts
 
Hi Chasmo
I had a somewhat similar problem. This sometimes happens when the AC power line is not 100% grounded tho that wasnt my issue. When the AC is not 100% grounded, your speakers will probably pick up the 50/60hz AC frequency which you are hearing as a humm. My problem got solved by using a balanced interconnect between my pre and power (everything else is single ended) - dont recall if the Forte 5 has a balanced option. I also inserted a transformer based power conditioner which helped make the background quieter.
Best regards
JB
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