Stereo amplifier fault

This is NOT a Sonos question; but I don't haunt other fora, and there may be some enthusiasts here that have an answer, hence I am seeing if I can get some advice here.
I have a NAD amp of 2012 make, that has an amber light when on standby. When the on button is pressed, it takes a few seconds for the amber to turn green, and for the amp to play. All this, in silence.
The fault I am seeing now is this: the light turns to green, and after a few seconds reverts to amber, with a very loud pop from the speakers. Obviously, the amp does not play then.
Also, sometimes, this does not happen; the amp performs the way it always has.
Questions therefore:
  1. What could be happening?
  2. What is the fix?
  3. Until the fix is in place, any risk in playing the amp, given that the speakers will pop for every failed attempt?
Thanks for any insights.

Best answer by Airgetlam 9 August 2019, 03:47

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14 replies

I don't own NAD amps, so take this with a grain of salt, sir.

What it sounds like is a fault in the electronics (perhaps a capacitor issue?) inside the device. Any chance there's a dealer in India that you could send it to?
Not sure where you are, but it looks like they have a dealership with offices in Mumbai:

Kripa Electronics
G-52 Roopmangal Building, 16th Road and Main AvenueVithaldas Nagar, Santacruz West
Mumbai, 400052
+91 22 26051781
Thank you for that effort - although Mumbai is a hundred miles away, it is worth a shot if I can't find help closer by.
I suspect it is a capacitor issue, or something else in the output stage seeing that the pop is loud even when the volume is at zero.
The other thing is that the issue comes and goes - that make it more difficult to pin down. And every start is a bit of a chance being taken on possible damage to speakers if it does pop up its head again.
Likely, there is a fault in the NAD and it's own protection circuit is shutting the unit down.

As a power amplifier turns ON the speaker output terminals remain disconnected in order to protect the speakers from transient "pops" as the amplifier starts up. After a few seconds the amplifier circuit settles down and the speakers are connected. If you are near the amplifier you may hear an internal "click" as the speakers are connected. At this point the amplifier's "protection circuit" takes over. This protection circuit is designed to protect the speakers from an amplifier failure and protect the amplifier from external faults. (Note that I'm not familiar with the NAD details, but a few designs will not exhibit any "click")

If you have a voltmeter, disconnect the speakers, make sure that the input signal is zero, and monitor the DC voltage on the amplifier's speaker terminals. After the "click" the speaker terminal voltage should be very close to zero. Amplifier designs vary, but the protection circuit will usually take action if the DC output voltage (many times called the "output offset voltage") is not close to zero. The protection circuit is also monitoring the output current. Even if the offset voltage is only 0.1 volts, you will be able to hear a quiet "click" from the speakers. Amplifier documentation that I've seen suggests repair action if the offset voltage is higher than 0.1V.

In your case I recommend not connecting speakers to the unit until it is repaired because there is high probability of speaker damage and more severe damage to the amplifier.
Yep, most protection circuits monitor output for DC. Could be as simple as readjusting the DC offset pots, or something worse. IME, NAD gear has always been built to a price point, and difficult to repair (I’ve had at least three, thrift store finds), so hopefully it’s just the offset adjustment having drifted.
Sometimes DC offset pots become noisy.

Also, at this age some of the solder connections can begin to break down. A very close visual inspection can save hours of troubleshooting and unnecessary component replacement.
Thanks for the advice, gents, very useful. Finding repairmen that know what they are doing is hard in India, though none of them are expensive - and I suspect there is a chicken or egg situation there!

  1. What buzz describes happening at start up where protection circuitry is built in, is exactly what happens with the NAD when all is well. What is happening now is that after the click when the ON/OFF light goes green, there is another click and the light goes back to amber, with pops of varying loudness. This, whenever the defect surfaces.
  2. I was advised some years ago, that the workaround was to leave the amp with mains power always on, in standby mode, when not in use - because turning off mains power does something inside the amp that does not happen in standby mode. For a few years, this workaround did the trick. And even now, it seems to do the trick more often than not, but not always, hence the concerns.
  3. How does one readjust the pots, as chicks suggests?
  4. Finally, since I have time on my hands - as evidenced by my post count:-) - I don't mind delving into this myself, borrowing a voltmeter, or even buying one because it can be used for other issues around the house. The one thing that worries me is the advice about lethal voltages inside the amp, even when it is not connected to the mains. So far, my basic precaution about fiddling with broken things is to have the mains power plug pulled out before doing anything, except in the case of TVs and valve kit, where I know that just this isn't enough. In the case of solid state amps, what has to happen AFTER the main plug has been pulled, to render the inside of the box safe to explore?
Again, thanks for the tips.
PS: I don't mind if the amp breaks for good in my trying to fix, but I would be unhappy if something happened to me.
The reason to pursue this even given the age of the amp - it is a 2008 buy, not a 2012 one - is that when it works as it ought to, it does the job as well as any other amp I know, so it seems a waste to just junk it.

I have an older Rotel of 2003 make at my daughter's home that still works as when new; but that is down to a better build quality than NAD, I think, at about the same price point.
Head on over to HiFiEngine, sign up for a free account, and download the service manual, if it’s there. Should have location for the pots, and adjustment procedure. Newer gear may or may not be designed for service, sadly, unlike the great old ‘70s gear, which is still hugely popular.
Double post
Head on over to HiFiEngine, sign up for a free account,
Can you do this for me? It does not let me register, saying it is not available for my region. Since it is free anyway, I can't see any legal or moral obstacle:-).
My amp is listed there with its service manual linked - C325BEE.
If you are able to do this, I will send you my email address via PM, to email the manual file to.
1. Level power on for a minimum of 5 minutes
2. Connect a DC voltmeter toTP1 and TP2 ,adjust VR22 for 4mV reading on voltmeter. 3. Connect a DC voltmeter toTP3 and TP4 ,adjust VR12 for 4mV reading on voltmeter.
Adjust the pot VR3 to make the DC voltage of the point of TP10 to the same as TP11

I see that there are other places to download the service manual from, and I now have it with me; mulling over next steps for a bit now.