(Amp fault) Diagnose this noise? 7 second video

sjbrodie

Established Member
Joined
Apr 12, 2012
Messages
65
Reaction score
4
Points
20
Age
36
Amp is a NAD3020i, an upgrade to my entry level cambridge however definitely now a vintage model.

This noise occurs only occasionally in the left channel. Seems mainly vocals and higher frequencies are broken up with distortion before returning to normal. Interestingly, I've connected the amp's "rec out" to a Line In on my sound card and recordings made on my computer pick up no disturbance from the amp's output at all. The distortion occurs through speakers and the headphone jack.

I'm no expert so I did have a technician look at it with a solder iron when I bought it. He said he could detect no problems but did suggest rotating the pots occasionally which can get dirty.

Take a look at the video and let me hear thoughts on this. Could the problem simply be dirty pots? I hope so since I really love this amp. My first quality entry level...thanks guys

 
Sorry about the advertising links. These were NOT INTENTIONAL! Post has been approved by mods...
 
Last edited:
I would classify that as gross disturbance, rather than mearly distortion. A worn pot where the wiper was jumping off from the carbon track could give that effect. But just moving the wiper up or down a little should put you on a lesser used section
As a service technician, those intermittents are the worst type of fault, so it could be anything else , a loose connection anywhere, including inside a component, and responding to the vibration and perhaps a mechanical resonance.
The only thing you know for certain is that it is in the left channel power amplifier stage. A typical repair strategy is to systematically freeze each component in turn using one of those freeze sprays and see can the problem be made permanent, then it can be fixed.
 
The amp should also have a pre amp out separate from the line out. Its connected to the power in by 2 solid metal u shaped bars. The pre out goes through the volume pot whereas line out does not. Any problems with this output? This isolates the problem to the volume pot or the power amp section.
 
The amp should also have a pre amp out separate from the line out. Its connected to the power in by 2 solid metal u shaped bars. The pre out goes through the volume pot whereas line out does not. Any problems with this output? This isolates the problem to the volume pot or the power amp section.

Yes, I have the pre amp out but to be honest I've left it alone since buying the amp as I'm ignorant about how to use these/incorporate it into a bigger system. Could you please explain how to test this output? Thanks :)

Am I wrong in assuming I've already isolated the problem to the volume pot since no disturbance is passed through my Line Out? As I briefly mentioned, the NAD's line out is fed into my laptop for vinyl recording and all of my recordings are perfectly balanced and clean yet playing the same source has produced distortion through the left speaker and headphone.
 
Last edited:
It depends if the headphone output is after the pre amp stage. So far we know the problem is after the source selector. It could be the volume pot (just needs a clean) or the output stage (likely more expensive). The pre amp output on the back can be used just like the line out. Connect the pre amp out to the line in on your soundcard to see if that's the problem.
You can also connect your soundcard line out to the power amp input on the NAD to test that part of the amp ***CARE*** that you start with the soundcard volume set right down to start off!
 
I've just read the headphone output is after the pre amp stage so you need to try to test the volume pot as suggested in my previous post if you can.
 
Just want to thank everyone for the replies. I've showed the thread to a technician who may be visiting this week and will repost with further updates
 
Yes, I have the pre amp out but to be honest I've left it alone since buying the amp as I'm ignorant about how to use these/incorporate it into a bigger system. Could you please explain how to test this output? Thanks :)

Am I wrong in assuming I've already isolated the problem to the volume pot since no disturbance is passed through my Line Out? As I briefly mentioned, the NAD's line out is fed into my laptop for vinyl recording and all of my recordings are perfectly balanced and clean yet playing the same source has produced distortion through the left speaker and headphone.
Have you isolated it to the volume controls?, what you have done is confirmed that the problem is post the preamp. ... Not necessarily... In many amplifiers there is a preamp stage terminating at the line output stage... , Now the power stage is driven via the volume control, and the headphone jack is often taken from the output of the power stage , via a resistor dropping power network. , Any defect in the power stage could have the effect noticed.
 
Last edited:
The pre amp output on the back can be used just like the line out. Connect the pre amp out to the line in on your soundcard to see if that's the problem.
You can also connect your soundcard line out to the power amp input on the NAD to test that part of the amp ***CARE*** that you start with the soundcard volume set right down to start off!

Just a small update for now

I carried out both these tests. With the pre amp out, I noted some minor disturbance as I was manipulating the controls (although nothing dramatic) The power amp in played perfectly and seemed flawless. I feel I should stress again the signal "dropout" heard in the video is still only a very occasional annoyance and seems to return after a few weeks for a short period. I will eventually clean the controls first though and report back.

Thanks for the suggestion
 

The latest video from AVForums

Is Home Theater DEAD in 2024?
Subscribe to our YouTube channel
Back
Top Bottom