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Naim 52 mono sound problem

toto

toto

pfm Member
Hello.

I am using naim 52 preamplifier.
Today I pressed the mono switch on the preamp and the sound was strange. The singer's voice becomes reduced and howls occur.
It seems as if a singer is singing in a cave. Volume is also reduced than when it was in stereo.
I would appreciate some help as to what the problem is.

toto
 
toto said:
Hello.

I am using naim 52 preamplifier.
Today I pressed the mono switch on the preamp and the sound was strange. The singer's voice becomes reduced and howls occur.
It seems as if a singer is singing in a cave. Volume is also reduced than when it was in stereo.
I would appreciate some help as to what the problem is.

toto
Click to expand...
press that button again and all'll be fine ;)
 
Not seen or heard this before, but the mono switch just switches a relay that ties the inputs together on the filter/buffer section. For the kind of issue you're hearing then there's a serious fault with the filter boards, but that's unlikely given it all works in stereo. This definitely needs to go a test bench.

One thing that springs to mind is a faulty opto-coupler. These take the logic signals from the front panel boards and drive all the relays on the main boards. When they fail they can often drive more than one output simultaneously, so it's possible that more than one signal is being routed when in mono - I've seen these fail many times. Again, this needs fault finding with a signal generator and scope.
 
toto said:
I've pressed it a few times, but it's the same symptom.
Click to expand...
I meant it as a nudge šŸ˜Ž- that is, the 52 works perfectly in stereo (second press on the 'mono' button)... anyway, a professional's view has just been added, best to follow his advice
 
MJS said:
Not seen or heard this before, but the mono switch just switches a relay that ties the inputs together on the filter/buffer section. For the kind of issue you're hearing then there's a serious fault with the filter boards, but that's unlikely given it all works in stereo. This definitely needs to go a test bench.

One thing that springs to mind is a faulty opto-coupler. These take the logic signals from the front panel boards and drive all the relays on the main boards. When they fail they can often drive more than one output simultaneously, so it's possible that more than one signal is being routed when in mono - I've seen these fail many times. Again, this needs fault finding with a signal generator and scope.
Click to expand...
Thanks for your help.
I discovered something new today.
I found that when I turn it on and play music in mono, it works normally for a few seconds, but then the sound gradually gets quieter and howling occurs.
To replace the opto-coupler, have to remove the top main board, but I have a Metcal desolder and station.
 
OK, this sounds like a power supply fault now. Equally, I've yet another fault mode whereby there was a faulty 0v return in the Burndy lead. At this stage I'd have the power supply and 52 open checking all power rails and continuity between main board and power supply through the Burndy.
 
MJS said:
OK, this sounds like a power supply fault now. Equally, I've yet another fault mode whereby there was a faulty 0v return in the Burndy lead. At this stage I'd have the power supply and 52 open checking all power rails and continuity between main board and power supply through the Burndy.
Click to expand...
I am using 52PS. I replaced the LM317 on the logic circuit power supply board because there was no sound.
I'll swap with my other supercap. Then, I can more easily resolve whether it is a 52PS problem or a 52 head unit problem.

Many thanks.
 
This is the final result.

Tested with supercap to see if it was a problem with 52PS : Same symptom.
52 head unit opto-coupler replacement : same symptoms
Bundy cable replacement : same symptom
Change 52 to 32.5 : Same symptom

The conclusion is that my CDP seems to be the problem. However, it is strange that only when switched to mono, the sound becomes smaller and the singer's voice begins to howl.

toto
 
Some old CDPs used a shared DAC the Philips CD104 was an example. The BBC had the same issue when the reception conditions forced the signal to mono.

One channel is slightly lagged behind the other, mixing to mono causes cancellation at some higher frequencies.
 
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I finally solved the problem.
I checked the source cable as advised by colasblue.
The connection on one channel was wrong. Re-soldering solved the problem.
Thank you to everyone who helped.
 
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