After more than 5 years of trouble-free listening pleasure, my stereo 35 has developed a new 60 cycle hum. It's also making a louder pop on shut down than it has before. Nothing looks amiss, bias is fine, tubes relatively fresh.
Any thoughts?
new hum
6 posts
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by EWBrown » Thu Mar 05, 2009 7:31 pm
First of all, unplug the input cables from the amp, and see if the hum is still present. cables can and do go bad. Or the "source" is generating this, via a ground loop or some other fault.
If that doesn't work, then:
It's ostr likely a tired electrolytic in the PSU, or perhaps a less than "perfect" ground connection, make sure that the screws on the terminal strips are reasonably tight, and that the crimped on lugs are properly terminated.
Of course, if you soldered all the "externals" direcdtly to the board, then this does not apply...
A simple power-off "pop" cure is to connect a 0.001 uF, 1KV ceramic disc cap across the power switch contacts. That's an "old school" trick. Yellow_Light_Colorz_PDT_11
HTH
In John Broskie's latest blog, he describes a truly "paranormal" persistent hum problem. The "paranormal" part was that the speakers still hummed even when disconnected from the amp :o
No, it wasn't ghosts, UFOs or the CIA. The cause was the old house wiring, which was the old style parallel (knob and tube) wire system, and the wires passed directly under the speakers (below the floor) and the crossover inductors were picking up the magnetic field being radiated from the wires. The cure was to move the speakers to another location.
The "suspect" wiring probably looked like something this:
Not exactly up to current NEC codes :o
/ed B
If that doesn't work, then:
It's ostr likely a tired electrolytic in the PSU, or perhaps a less than "perfect" ground connection, make sure that the screws on the terminal strips are reasonably tight, and that the crimped on lugs are properly terminated.
Of course, if you soldered all the "externals" direcdtly to the board, then this does not apply...
A simple power-off "pop" cure is to connect a 0.001 uF, 1KV ceramic disc cap across the power switch contacts. That's an "old school" trick. Yellow_Light_Colorz_PDT_11
HTH
In John Broskie's latest blog, he describes a truly "paranormal" persistent hum problem. The "paranormal" part was that the speakers still hummed even when disconnected from the amp :o
No, it wasn't ghosts, UFOs or the CIA. The cause was the old house wiring, which was the old style parallel (knob and tube) wire system, and the wires passed directly under the speakers (below the floor) and the crossover inductors were picking up the magnetic field being radiated from the wires. The cure was to move the speakers to another location.
The "suspect" wiring probably looked like something this:
Not exactly up to current NEC codes :o
/ed B
Last edited by EWBrown on Mon Mar 16, 2009 5:34 am, edited 2 times in total.
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EWBrown - Insulator & Iron Magnate
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by EWBrown » Fri Mar 06, 2009 7:15 am
Look for any "goo" leaking out of the cap, and perhaps the bad one may actually feel warmer than the rest of them.
/ed B
/ed B
Real Radios Glow in the Dark
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EWBrown - Insulator & Iron Magnate
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- Joined: Wed Mar 19, 2003 6:03 am
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new hum
by Lafish » Sun Mar 15, 2009 9:25 pm
With no cables attached, the amp of course had considerable noise and hum. But the mere act of removing and reattaching them has dropped the level to a very modest amount. Duh...
It really is a very nice sounding amplifier.
Larry
It really is a very nice sounding amplifier.
Larry
- Lafish
- Posts: 14
- Joined: Tue Apr 24, 2007 5:06 pm
- Location: San Francisco
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