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Marantz 1200 volume issue

Salbreth1

Salbreth1

Active Member
Hey guys, So I just finished a 1200b and noticed that I still have audio out of both channels when the volume is at zero. At first i figured a bad pot but out of curiosity I plugged in a 1200 I'm getting ready to start and it has the same problem. Even when the gain switch is on low I have audio from both units. Coincidence? Maybe the higher output from my input devices? Thanks

Sal
 
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I've seen some vintage solid state Scott integrated amps do that. I've had an A436, A437 and A457 and they all do it the same, a bit of treble coming out the speakers with zero volume....for those it seems a design fault, but I can't say about the 1200B....
 
Some of the new sources put out as much as 2.5v so yes it "may" be normal. Are there any distortions or other inharmonious sounds associated with it????

Originally in the 60s and 70s sources put out something like 0.5v or some other low value. That you would have just heard a whisper. At 2.5v you really don't need a preamp but just an attenuator. Unless you need impedance smoothing/matching like my VTA ST-70. Sounds great with the preamp but not so good without.
 
Which outputs have audio when the volume is down?
Tape out and Scope are not controlled by the volume control.

Tom
 
The pre outs. I noticed I had output on my scope while making adjustments. I haven't gone any further yet, but I thought it was odd that both the 1200 and 1200b have the same issue. The 1200 is original inside. I ran the pre outs to another amplifier with the same result so that rules the amps out.
 
I have both a 1200 and 1200B and neither have this problem. There is a Service Bulletin that addresses a "cross talk" problem in the 1200's after serial number 3500 - Chris
 
Ah ha, thanks chris. Both units are over 3500. When I get a minute I'll look for the bulletin. Un real that its happening in both units.
 
Ok, so the bulletin says that it applies to the phono section. That said, the ground connection at the selector switch was already in place being that my model number is after 5900. I clipped the specified jumpers anyway with no change. Then I ran white noise into both channels with the volume down. and probed around a bit. When I applied a little pressure to the volume pot leads it almost went silent in the left channel and stayed that way. Gently moving the leads dramatically changed the amplitude at zero volume. so I pulled the pot and resistance is all over the place. I'll order a dual 50k with taps and hope that's was it. I have a new Alps pot here but dimensionally it wont fit. :confused: Maybe I'll remotely connect it just to make sure that's my problem.
 
Eureka! Remote pot solved the problem! Now I just need to find one. Nothing on ebay, Alps wont fit. Anyone have a source?
 
I think all those 1200s had weak volume pots. That was the first thing that went on my 1200.
 
Salbreth1 said:
Eureka! Remote pot solved the problem! Now I just need to find one. Nothing on ebay, Alps wont fit. Anyone have a source?
Click to expand...

The 3300 preamp and the 1200's preamp section are the same ... just flipped over. As Catrafter knows, I went through a lot of problems to figure out and replace the 3300 volume control. I ended up modifying two volume controls to fit on the circuit board. The first one was a 50k pot.... but that 50k pot, although I got it in and it worked, the volume control did not provide enough control at lower volume, like my 1200 does. So I believed that the schematic 50k was not correct and looked for a 100k.....
I found only one 100k pot and did a modification to get it to mount on the board. Has been working perfectly for almost a year.

$6 at Radio Shack..... It's smaller, but works fine.... only issue is that it measures 90k and not 100k.....

btw: I will get some crosstalk if I run the Sony cd player on aux at its normal output. Had to put an output pot on the cd player to bring it's output down similar to the preamp.

Hope this helps......
 
Thanks guys. The romote pot i used was a 250k. It was smooth with nice control but id rather get something closer. I more bummed that other likey has the same problem. Ill be stalking ebay in the mean time.
 
I just seem to remember the schematic having one value vc and the actual unit having another.Also the legs on the vc are wired wired. Make sure you remember which leg goes were. One channel is wired up normally while the back end of the pot is wired in reverse. Use headphones to test it out
 
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