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A hum in the Sherwood

dyche01

dyche01

"Buy high. Sell low"
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My current office setup is an old Sherwood S-7110B driving a pair of Mission 760 speakers. Apart from the radio, my inputs are a computer and iPad, which run through an ODAC from JDS Labs. The sound from this system was really great until a couple of nights ago when I noticed a distinct 60 Hz hum from the right channel. The left channel was fine until today and now it's humming away as well. The hum is not loud (just at the threshold of hearing when no music is playing) and it is not affected by the volume control or any of the front panel buttons (loudness etc.).

Sounds like either an amp or power supply issue. Anyone had experience with these old Sherwood receivers? Any advice?


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The great benefit of Audiokarma? Even when nobody replies to your thread, you still get an answer to your question.

After a little searching and reading I decided the problem might not be a faulty component but a bad ground connection. So, I pulled the cover (nude photos below) and started tightening screws and jiggling wires. Tightening the screws on the transformer helped, but when I tightened one of the corner screws on the main amp board (marked with a red arrow in the third photo) the hum magically disappeared! I mean completely disappeared!

The filter capacitors still looked mighty fine, so I will leave them as they are.

Now I am listening to some Bill Evans piano riffs, with dead silence between the notes: just like he intended.


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Congratulations on the simple fix! I have the same model receiver and am experiencing a similar type hum. Will try your procedure and see what happens.

It appears that the original power on/off switch has been replaced with the red push button. Can you share the type and specs for the replacement?

Thanks!
 
Good eye. The modification must have been done by one of the previous owners after the original power switch broke. I have read that this switch is the Achilles' heel of the old Sherwoods and that many break after being sprayed with Deoxit. Whoever added the red push-button switch also added a rocker switch on the power cord. They weren't taking any chances!

The hole in the faceplate was drilled so cleanly, and lined up so well with the other controls, that I didn't realize the switch was an after-market mod until I looked at the manual. The switch has no manufacturer or part name that I can see. I think pretty much any good quality switch that is rated for AC line voltage will do. In the photo you can see the empty terminals on the back of the original pot/switch where the wiring for power input was previously attached.

And be careful not to over-tighten any of the screws!

switch.jpg
 
Yep, that power switch was one of the problems with my receiver. With suggestions from this forum, I simply clipped the two leads and temporarily spliced them together with a wire nut. It is presently connected to a power strip, but I may go with the inline rocker switch. Thanks for the info. Will be extra careful with them screws! :)
 
Thank you for following up on your post with the solution. Fixed the hum in my 7110B!
My power switch is going strong, but I did recently deox the switch. :oops:
 
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