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1200 Preamp-Amp Jumpers / Hum

ocdecio

ocdecio

The proof of the restoring is in the listening.
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The 1200 I am working on has both amplifier boards working properly, so I decided to connect it to the preamp for some more testing. However when I use a "custom" jumper (two RCA connected with a short cable - I don't have the originals) I get a lot of hum, like real loud. These jumpers connect both the ground and the signal.

However if I only connect the middle part (not the ground) by inserting them half way through I get clear sound, no noise of any kind and the amp works pretty much normally.

Are there cases where we should actually use only the middle connection and NOT connect the ground from one side to another or am I looking at some more issues that need resolving?
 
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sanjib said:
Did you try other RCA cables?
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I did. If I connect the outside part (ground) I get noise. If I connect a different preamp into the amp input everything works, no noise. I put a scope with the jumper all the way in and the noise isn't there.
 
If you see the original metal jumper connection, I believe it never connects the outer parts!
 
sanjib said:
If you see the original metal jumper connection, I believe it never connects the outer parts!
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If you have the originals, would you mind checking if yours do? If they don't I'll just fabricate a jumper with 8AWG wire. Thanks!
 
I don't have Marantz 1200 integrated. But all the other receivers I have, the jumper just connect the inner part. The Marantz integrated I have is 1152DC it has no jumpers. Here is a picture of the rear side of the 1200 I got from the web. It looks like the outer part is plastic (I may be wrong).
1200 back.jpg
 
I have a 1200 with original jumpers. I checked, and if the question is whether the two outer shells are connected - yes, they are.
 
Steven Tate said:
I have a 1200 with original jumpers. I checked, and if the question is whether the two outer shells are connected - yes, they are.
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Much appreciated for checking! I probably have some cold/loose connection somewhere that I will chase down.
 
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