Nigel, check for variation in the bias current on the affected channel and also see if that channel's heatsink is heating up. If the noise is constant regardless of volume setting or mute, you are correct, it is the driver board.
RobNYC
On Monday, July 22, 2024 at 03:20:26 AM GMT-5, Nigel Pugh pughn@npsyssoft.force9.co.uk wrote:
Thanks everyone for the replies on this. I forgot to mention, the one amp was rebuilt in 1997 and the other in 2007, including all electrolytics and the filter caps. The static and rustling sounds are present at the same volume, regardless of muted or not. Suggesting an issue on the power amp side I guess. Repeated selecting and cancelling seems to clear the problem. I'm just intrigued that for both jukeboxes in the same house started playing up at the same time - a few weeks of not being used. RegardsNigel
On 22 Jul 2024 at 09:00, Chan Gade via Jukebox-list jukebox-list@lists.netlojix.com wrote:
Causes are: Electrolytic capacitor leaking or failing to "form". Since these amps don't have a DC sensing circuit to disconnect the speakers, they are kept connected during the inrush at turn-on. As electrolytic caps age, this sort of noise can become more noticeable. It should only last a few seconds.
Noisy carbon resistor.
Noisy transistor.
The volume control sits between the preamp/AGC board and driver board. If the noise varies with volume control, it points to the preamp/AGC board.
Nigel, that amp is nearing fifty years old, it likely need a rebuild.
Moisture can also cause this, but probably not the case here.
Regards,
RobNYC
On Sunday, July 21, 2024 at 01:04:24 PM GMT-5, Nigel Pugh via Jukebox-list jukebox-list@lists.netlojix.com wrote:
I went on holiday and didn't use my Sunstar or Topaz for a few weeks. Both have SHP-3 amps. I haven't really had time to investigate this issue but am curious for others views.
Turned on the Sunstar and there was a rustling sound on one channel. Upon playing a record this turned into a loud static popping sound. Very sharp. Rejected the record and after selecting and rejecting a few records, all was fine. It wasn't static groove noise , it was heavy electrical popping static.
Then, next day, played my Topaz, and to my surprise, the same issue here. Probably worse. So it looks like a bit of lack of use has caused the same issues. My hunch is the board connectors, can anyone point me more accurately to the issue ?
Mute relay on Sunstar is perfect and clean.
I also noticed, that on unplugging the RCA phono inputs on this amp, it really screws up the sound when putting them back in. Muffled, quiet, flat. Switching the machines off and on a few minutes later fixes this. I don't understand why.
So why did lack of use for probably 2 weeks maximum cause the same problem in both jukeboxes ?
Nigel
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