Hi
I'm in the process of repairing an NAD 314. The Problem is, that the amplitude of the right channel is much lower than on the left channel. The signal of the right channel also has a slight phase shift compared to the left channel. I already checked that the output of the preamp is fine on both channels. They are equal.
The yellow curve is the faulty right channel, blue is the left one.
What could cause this? What should I check?
I'm in the process of repairing an NAD 314. The Problem is, that the amplitude of the right channel is much lower than on the left channel. The signal of the right channel also has a slight phase shift compared to the left channel. I already checked that the output of the preamp is fine on both channels. They are equal.
The yellow curve is the faulty right channel, blue is the left one.
What could cause this? What should I check?
- As the signal is fine after the preamp, it cannot be a faulty switch. There's no switch in the power amp. It's also not the speaker relay, because the signal is already low before the relay.
- The outputs are most likely fine, because the amp drives speakers without a problem, there's not even DC on the output, but the level is low on the right channel.
- Power supply is fine, otherwise the problem would be on both channels.
Are the DC Offset and final stage BIAS adjusted to spec?
Can you probe (o-scope) the input to the driver stage (right side of R316) on both channels to compare?
Probe the feedback node (DC offset circuit) at the junction of R338 + R336 (again both channels to compare).
Can you probe (o-scope) the input to the driver stage (right side of R316) on both channels to compare?
Probe the feedback node (DC offset circuit) at the junction of R338 + R336 (again both channels to compare).
I am able to adjust DC offset and bias to spec on both channels.
This is the input to the differential stage after R316. Left channel is blue, right (broken) channel is yellow. It's fine to this point.
This is at the junction of R338 and R336. It's fine there too.
Not sure what this tells us, but the problem seems to be there at the base of Q318.
What to check next?
This is the input to the differential stage after R316. Left channel is blue, right (broken) channel is yellow. It's fine to this point.
This is at the junction of R338 and R336. It's fine there too.
Not sure what this tells us, but the problem seems to be there at the base of Q318.
What to check next?
I would begin by checking the feedback network has the correct values in both channels. The channel with most output might be the faulty one.
As you have the same input signal to each channel you need to check these three parts.
The amp should have a voltage gain of approximately '17' meaning 0.1 volts peak (or rms, whatever units you want) as an input should give 1.7 volts output.
As you have the same input signal to each channel you need to check these three parts.
The amp should have a voltage gain of approximately '17' meaning 0.1 volts peak (or rms, whatever units you want) as an input should give 1.7 volts output.
Ok I checked the gain of the 2 channels. It seems that the left channel actually has a gain of about 17, the right channel has much less. How did you calculate that?
The resistors measured okay, but the 220uF cap measured open.
After replacing the cap, the issue is gone.
Thank you very much!
The resistors measured okay, but the 220uF cap measured open.
After replacing the cap, the issue is gone.
Thank you very much!
Calculated from the feedback factor which is set by those two resistors. The gain is (3k91/240)+1 which is 17.3.
The cap reduces the gain to unity (1) at DC while at AC it should have no effect as it passes all audio frequencies without loss.
The cap reduces the gain to unity (1) at DC while at AC it should have no effect as it passes all audio frequencies without loss.
I've not come across those either. I'm going to go as far as to say they are probably a part chosen on cost alone and I would seriously consider replacing all such parts with recognised modern replacements.
That part is extremely lightly stressed and so it is a rather strange failure mode.
That part is extremely lightly stressed and so it is a rather strange failure mode.
E|C?
NAD, of all makes, cheaping out!
If you value your set, replace all of those suspicious capacitors with those from a reputed manufacturer.
NAD, of all makes, cheaping out!
If you value your set, replace all of those suspicious capacitors with those from a reputed manufacturer.
There is a stylized lower case 'e' or 'r' in the capacitor marking, so it is rE|C or eE|C...
That rings any bells with the European members?
But those are end of life, better replace them with new ones.
That rings any bells with the European members?
But those are end of life, better replace them with new ones.
OK. Thx.
Same brand as in the 314 that I got off ebay....plus Marcon and NCK brands.
For me five were dead open and all located in the power supply.
Agreed.
NAD, good designs, poor execution on the manufacture (out-sourced factories); needless I'm a follower.
Why is it that all the bean counters I know act as if the money is going from their pockets to the suppliers, rather than from the business that pays their salaries?
Now NAD is part of a Far Eastern group, so how they maintain the product quality remains to be seen, and what kind of new products sell in an increasingly Class D and DAC world....
Likely they will do an Audi, which is a dolled up Skoda.
I would buy Toyota.
Now NAD is part of a Far Eastern group, so how they maintain the product quality remains to be seen, and what kind of new products sell in an increasingly Class D and DAC world....
Likely they will do an Audi, which is a dolled up Skoda.
I would buy Toyota.
Would you be willing to go a little higher level with this explanation for someone like me, who doesn‘t really understand what I’m looking at?