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NAD 3150 Channel distored.

HIFIuk

HIFIuk

New Member
Hi I'm new here so thanks for accepting me.
I'm in the process of recreating my old 1980s system. I have my 2 Roger's LS7 speakers that seem to be ok. The amp isn't well unfortunately. One channel is distorted (only at.low volume as far as I can tell).
Same distortion via the headphones too if that makes a difference...

I have switched over the pre out / main in connections and the issue remains on the same channel. Google suggests that if this is the case it's the power amp, driver, or bias/DC offset circuit. I've yet to clean all the pots with switch cleaner so it may just be this but I suspect something has failed. I don't have a scope. Any suggestions or anyone else had a similar issue?
Thanks in advance!
 
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I have fixed noisy and distorted channels with a good cleaning.

Bias can be checked but may not my first step. Just be careful when poking around.
 
You fed a low signal into the AMP IN RCA and it was still bad?
Here's a video of the bias:
 
milo63 said:
You fed a low signal into the AMP IN RCA and it was still bad?
Click to expand...

This would see if the problem is in the amp section or preamp section.

I use an old iPod but anything with a variable output. Just start very low volume and slowly turn up.
 
Assuming all controls properly cleaned, clean rear panel interconnect RCA's. Remove hoops, spray and insert hoops to work the internal levers. There are three switches on the back panel that should also be cleaned.
 
SoCal Sam said:
Assuming all controls properly cleaned, clean rear panel interconnect RCA's. Remove hoops, spray and insert hoops to work the internal levers. There are three switches on the back panel that should also be cleaned.
Click to expand...
Yes that's the first thing to do. I'm getting some decent switch cleaner and going in deep - but carefully...
 
SoCal Sam said:
Assuming all controls properly cleaned, clean rear panel interconnect RCA's. Remove hoops, spray and insert hoops to work the internal levers. There are three switches on the back panel that should also be cleaned.
Click to expand...
Yes that's the first thing to do. I'm getting some decent switch cleaner and going in deep - but carefully...
 
milo63 said:
You fed a low signal into the AMP IN RCA and it was still bad?
Here's a video of the bias:
Click to expand...
Thanks that's a.great help.i just had a cd player in the aux input. The Distortion seemed to dissappear when the volume was very low on the NAD and the got worse as I turned it up. The input signal level never changed.
 
My first thought was dirty relay contacts however above post gives opposite performance.

Suggest connecting a CDP with variable output or iphone/pod/... to MAIN-IN RCA's, set CDP/Ipod volume to minimum. Play audio, increase vol slowly, check for distortion through headphone/speakers, post results. No distortion suggests preamp/switches? issue.
 
I've found NAD have small low voltage Electro caps in the signal path. They will at some point cause problems. You will need an oscilloscope Or start replacing them till it's fixed. It will take time & patience. All the caps are at the end of their life & replacing any of them is not a waste.. Use solder wick to unsolder from the boards & note polarity of caps.... Lovely amp when working.
 
Also keep in mind that the 3150 PRE uses an OPAMP, seen issues with failing power supply (regulators) to the opamp however this affects both channels.

First up, confirm if it's a pre or power amp issue.
 
making crap said:
I've found NAD have small low voltage Electro caps in the signal path. They will at some point cause problems. You will need an oscilloscope Or start replacing them till it's fixed. It will take time & patience. All the caps are at the end of their life & replacing any of them is not a waste.. Use solder wick to unsolder from the boards & note polarity of caps.... Lovely amp when working.
Click to expand...
Excellent thanks for the advice. I need to buy a cap kit from somewhere...
 
HIFIuk said:
Excellent thanks for the advice. I need to buy a cap kit from somewhere...
Click to expand...
A cap kit almost never solves a defect. Get a scope, learn how to use it and then apply a test signal (1 kHz sine wave) to see what happens to it. Distortion on low volume is not caused by bad caps. Dirty contacts (as indicated above) or bad bias (ditto) is. But do check if it's the pre- or power amp. That's always a good point to start, even without a scope.
 
PE9ZZ said:
A cap kit almost never solves a defect. Get a scope, learn how to use it and then apply a test signal (1 kHz sine wave) to see what happens to it. Distortion on low volume is not caused by bad caps. Dirty contacts (as indicated above) or bad bias (ditto) is. But do check if it's the pre- or power amp. That's always a good point to start, even without a scope.
Click to expand...
Ok sure I think its the power amp because I crossed over the pre out / power in jumpers on the back and the issue remained on the same channel. I'm going to clean everything with decent switch cleaner on Wednesday and I'll take it from there.
Thanks for ypur help it's really appreciated -
Dan
 
HIFIuk said:
I'm going to clean everything with decent switch cleaner on Wednesday and I'll take it from there.
Click to expand...
There are no switches in the power amp except the speaker switches and the relays. Oh, you could tap those relays to see if the symptom changes. If it does you're in luck because you then just have to change the relays for new ones.
 
Does 3150 have relays?
It has a bridging switch in the power amp, that I do remember.

E: had to check, and there's a relay indeed, instead of typical NAD muting circuit.
 
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