Besides moving the amp, another thing you can try is turning everything else off on the same AC circuit, and if that still doesn't work, go to your breaker box and turn off every single breaker. You may have DC on one leg, caused by another device.
Another mechanical 60 Hz noise post
Checked the previous posts on this here, but can’t find anything that seems to apply to my situation.
To start, please check out this pic of my office system:
At the bottom of the rack, you’ll see my vintage Belles Model One, purchased new and well-loved. It’s been routinely used and never abused since I purchased it in 84 or 85. It has always been located 10’ or more from my listening position until now.
During a late-night listening session with my Stax SR-404 Signature cans through an SRD-7SBmk2, I heard a hum when I took them off to return the beer. Did the isolation drill and discovered the amp is making a physical hum. It does not put any hum out through either the speakers or the ‘phones.
I haven’t ripped it out of the rack yet; as long as I have the volume up, I can’t hear it. With nothing playing, the hum is about the same level as the radon extraction system that runs outside the right-hand wall. And time to take my workspace apart is very rare. Before I put it in the rack, I took the cover off, gently dusted the inside with air and looked things over. Discovered the plastic on the old speaker terminals had cracked so replaced them. Didn’t see anything else amiss and the caps aren’t bulged or leaking. When fired up, it sounds just as good as the day I brought it home. Listening to it now, in fact.
So here’re my questions: Not being able to find a review on it, is what I’m hearing an artifact of this very first Belles effort that I just never heard before? Since I will take the amp out and pull the cover off for an inspection in any case, what would be the most likely thing to look for?
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Thank you for the input everyone! I ran the isolation drill again and then powered the amp from a totally different circuit without any DC devices in it. That confirmed @ghdprentice and @jeffbij identified the most likely culprit. The transformer is definitely not toroidal, FWIW. When I get a chance this next weekend, I'll pull the amp out of the rack and give the transformer a hard look. I'd thought it the sound was too pronounced to be anything other than a vibration of some sort, so I'm going to check for loose bolts and such first. Hopefully, I won't have to rely on Professor Google for more involved repair. I really don't want to have to go that far if I can avoid it. Thanks again! |
@effischer - No problem. Glad to help. Just be careful. It only takes 100 milliamps to stop your heart. And at 100W into 4 ohms is 5000 milliamps.... If the plates are too loose or have delaminated enough, it is possible that some of the windings maybe broken and are shorted to the plates. Make sure the amp is unplugged and let it sit for a while. You may want to discharge any of big caps hooked to the power supply side. |
@jeffbij @ghdprentice - Kudos to you both - your advice was spot on. Got the rack apart this morning, got the amp out and cover off. This is the interior: Caps up front and transformer hung off the rear panel. It's very straightforward design with a sanitary execution. Once I started wrenching, I discovered that several fasteners had loosened including those holding the transformer together, one of which was looser than the others. Tightened everything up, powered it up and was rewarded with just the sound of capacitors energizing. Things got more interesting when I re-assembled my rack. You'll have seen from the prior pic that it's fully stuffed. Got it all back in place eventually and upright again. Powered the amp up by itself as a final check and discovered that I still had a mechanical hum, albeit much softer. Something was resonating somewhere. I put my hand on the cassette deck shelf and heard the hum soften. Touched the exterior of the rack itself and again got a changed amplitude. Then I realized the rack is laminated bamboo so uber-rigid. I pulled the vent piece out of the rack, raised the amp up off the rack base 1/2U and moved everything else up 1U. Hum gone, everything is just as silent as it ever was. I would never have thought that the bamboo rack itself could reinforce native component resonance; the Belles lived in an Anvil road case for many years along with the companion RGR 4-1 and a Tandberg TCD 440A without issue of any kind I guess vinyl covered fiberglass laminated particle board with aluminum edge and corner protection is less susceptible to this sort of thing. Who'd a thunk it? Now I know and have a happy result. Thanks again! |
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