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Sony ta-4650 inputs bleeding through?

T

TrevorBarten

Well-Known Member
My ta-4650 has a weird thing where if you have an input going into any of the line level inputs (haven't tried it with phono yet) and you switch to either the tape monitor or any of the other channels the signal from the input will be audible even if you have the volume knob turned all the way down. If you do increase the volume the amount bleeding through from the left channel does not change but it does become slightly louder on the right channel. If you switch to the channel on which you have the source connected the signal disappears when the knob is turned to 0. Anyone know what the issue here could be ?
 
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It’s probably cross-talk, or coupling of one signal to another, usually it’s capacitance coupling, proximity of one signal to the other. Sometimes it takes place at a switch. Fundamental to the design. I’ve seen some designs short out unselected inputs to minimize the cross-talk.
 
I think I have a Sansui that has plugs in back, like pre-main jumpers, that plug in to unused inputs. I assume their purpose is squelch interference from unused inputs? I have several receivers that also do as the OP indicates his unit does, usually not a problem as I don't use tape monitor or more than one source at a time except on certain early 70's units.

There is at least one set of circumstances though where I can see somebody might really want to use Tape Monitor; the early 70's sansui and HK's kill the dial lights when you switch to AUX or Phono. Using the the Tape Monitor input for your AUX input, you can at least keep the dial lights on while listening to your AUX. Doing this though I can hear faintly whatever the tuner is tuned to between songs from the AUX input.
 
I do actually like playing around with tape, but I don't think it really matter considering it's the same signal regardless? I find it hard to beleive that this is how it was designed. I mean maybe it was normal at the time but it seems kind off like a weird thing to have for a hifi amplifier. It's not the most complex amp on the inside but idk.
 
Crosstalk, or bleeding from one source to other inputs is normal in some units, I've seen it many times. I can't tell where it's happening at your amp, but the usual solution is to mute the unused source signal.
 
Looks like this service bulletin for NAD C300 addresses same problem.
 

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TrevorBarten said:
So basically I should recap the input circuitry? Seems easy enough. Might as well do a full recap.
Click to expand...

I would check location and type of capacitors mentioned in Nad service manual and find similar capacitors in Sony amplifier. I think they are not electrolytic capacitors.

Don't forget replaced problematic diodes, which may take down unobtainable V-FETs.
 
Anton-2000 said:
I would check location and type of capacitors mentioned in Nad service manual and find similar capacitors in Sony amplifier. I think they are not electrolytic capacitors.

Don't forget replaced problematic diodes, which may take down unobtainable V-FETs.
Click to expand...
Those have already been replaced. Thank you for the tip on the caps.
 
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