±2mV of 'wobble' in the offset in itself is not significant. It is a little unusual to see it moving around without a signal connected.
To check for dry joints see if prodding any of the driver or output transistors makes it jump around. To check for transistor junctions freezer spray is better than trying to heat transistors. Prod all the other componend inside the power amp stage rectangle with a chopstick too, and tap on the top of any electros.
I do this as part of final QA before handing back a repair, as well as a drop test where I lift each side of an amplifier in turn about 5cm and drop it back onto the bench. It sounds brutal, but faults don't 'heal' themselves and better to find them before putting the lid back on and putting it back into service.
To check for dry joints see if prodding any of the driver or output transistors makes it jump around. To check for transistor junctions freezer spray is better than trying to heat transistors. Prod all the other componend inside the power amp stage rectangle with a chopstick too, and tap on the top of any electros.
I do this as part of final QA before handing back a repair, as well as a drop test where I lift each side of an amplifier in turn about 5cm and drop it back onto the bench. It sounds brutal, but faults don't 'heal' themselves and better to find them before putting the lid back on and putting it back into service.
A design is just that if its specifications allow up to 30mv and if your tests show the same you are "chasing shadows " .
As I said it could be a thermal problem probably an active device,but the problem is that could be the way its designed , what you might be trying to do is improve the design.
As I said it could be a thermal problem probably an active device,but the problem is that could be the way its designed , what you might be trying to do is improve the design.
Try using an analog meter, or the scope to see how the DC is jumping around.
Digital meters have a sampling interval, so their readings jump around.
And yes it could be a design feature or a capacitor charging and discharging.
Also, try when it is playing music, not loud, say 10% output, and on speakers you can afford to scrap. Or use some sort of speaker protection like a capacitor.
Digital meters have a sampling interval, so their readings jump around.
And yes it could be a design feature or a capacitor charging and discharging.
Also, try when it is playing music, not loud, say 10% output, and on speakers you can afford to scrap. Or use some sort of speaker protection like a capacitor.
It's -30mv and +0v, but I hear exactly what you mean Duncan.
I was fiddling around with the idle current pots some and matched both channels at exactly 4 volts. I then re-trimmed the pots for the dc-offset and was able to get both channels to balance out somewhere between -0.4mv and -7mv with the fluctuation going on.
Been playing the amplifier with a Topping E30 DAC through a pair of NHT model 1.1 two way speakers bypassing the internal pre-amp for over 4 or 5 hours now and to be quite honest this little NAD amp sounds fantastic. Lots of detail and accuracy in the sound of the instruments.
I'm going to let this play continuously for 24 hours and then recheck the specs to see if anything could be improved.
Good points Naresh on the analog meter and capacitors. I do have an oscilloscope, but I would require some guidance from a member who has the knowledge, the will, and the patience to walk me through the areas on the amp to test.
Not to rain on anyone's parade, as I've been accused of doing sometimes......
But going over that amp's schematic, for what it is, being a lower-powered model, I find the circuit overly-complex and kind of goofy IMO.
What were the designers thinking when they drew that up?
Were they one of the "fanatics" we've all seen around?
But going over that amp's schematic, for what it is, being a lower-powered model, I find the circuit overly-complex and kind of goofy IMO.
What were the designers thinking when they drew that up?
Were they one of the "fanatics" we've all seen around?
DC offset is within limits now...
If it ain't broke...
Enjoy
Just spray all mechanical bits like trim pots, jacks and so on.
Note the trimmer positions and readings for future reference.
If it ain't broke...
Enjoy
Just spray all mechanical bits like trim pots, jacks and so on.
Note the trimmer positions and readings for future reference.
Well the analog meter is out since I don't see how it can read -millivolts...😕
But I can setup the scope and take some readings from the speaker outputs rather easily to see what the dc-offset voltage looks like on the crt.
Or OCD
Or trying to show off...like some others
In terms of volumes, a bit player.
Now possibly made in China, with a British tag.
Later, possibly owned by Chinese or other traders.
Sansui is gone, in the last days they were owned by a Pakistani guy, less than 20 employees in Japan, and all operations in China.
Denon is now Denon + Marantz, owned by somebody in the US, no idea of the manufacturing base.
Or trying to show off...like some others
In terms of volumes, a bit player.
Now possibly made in China, with a British tag.
Later, possibly owned by Chinese or other traders.
Sansui is gone, in the last days they were owned by a Pakistani guy, less than 20 employees in Japan, and all operations in China.
Denon is now Denon + Marantz, owned by somebody in the US, no idea of the manufacturing base.
Couldn't agree more.
I have rescued 3 Adcoms GFA-555 first editions and was able to follow their schematics rather easily and fix all three of them with ease. When I look at the NAD C320BEE schematics I do realize that it's got a pre-amp also siamesed into the amplifier circuit board too and that makes the whole thing much more complex for my rudimentary skills.
I just wish somebody with more knowledge on this particular NAD amp could chime in about the fluctuating dc-offset and whether its a design issue.
Put the analog meter on its lowest AC range, with music playing at the output .
This will make it act like a VU meter. See the max reading on the scale is not exceeded.
Then change to DC, idle amp, the needle should barely move, as the lowest scale you might have is 10 Volts.
Start the music, see what happens, DC scale.
If it goes too high, more than 03 then we have to see in more detail.
This will make it act like a VU meter. See the max reading on the scale is not exceeded.
Then change to DC, idle amp, the needle should barely move, as the lowest scale you might have is 10 Volts.
Start the music, see what happens, DC scale.
If it goes too high, more than 03 then we have to see in more detail.
I've repaired lots of NAD amps including C320s, but not specifically the BEE version. My tips are in the posts above. They work for me every single time on any amp, NAD or otherwise, with the same fault. BTW it is not a design issue. Nor is the offset critical, need to be matched or have any effect on TDN+N or anything else at the levels you are seeing. The biggest concern is that if it is wavering it may indicate a component is failing. Not being familiar with the BEE I'm not sure it that behaviour is normal, but you'll find the answer if you follow the tips I've given above.
Hi John,
I didn't mention it earlier as I've done everything you listed above in bold except the freeze spray since I don't have it readily available.
The rectifier board is separate from the rest of the PCB and I removed it this afternoon after poking all the resistors, capacitors and the two black transistor tidbits with a plastic mixing wedge and nothing immediately changed in the DMM lcd display.
After removing it rather easily from the chassis (as it's only 4 screws and about 7 connectors that need to be removed) I examined the solder joints and they look visually perfect.
What about Naresh's point pertaining to a capacitor that is failing and charging and discharging as the cause of the problem?
Naresh,
The dc-offset is not swinging wildly to extremes. It's just fluctuating up and down by -0.2 to 8 mv.
Sorry to be blunt but not of all the advice you are getting here is helpful. Offset and bias settings drift under normal conditions, which is why a range is given for these settings in service manuals. Failing capacitors and transistors usually show up with freezer spray (as in usually when they are frosty cold the fault goes away). If you've already done the tests above (even without the freezer), stop worrying and put the lid back on.
John is right, any faults would have come out in the long term soak testing done already.
You have not specified the time taken for the changes to occur in the readings, nor the scope and analog results, nor the status, as in music playing or not.
As the results are within the limits specified, leave the unit alone, for safety's sake just reflow all the input and output connectors, clean off the flux residue.
Put the lid back on, see how the speakers are protected, and enjoy the music.
If installed remotely in the attic, do something for failure when it occurs.
You have not specified the time taken for the changes to occur in the readings, nor the scope and analog results, nor the status, as in music playing or not.
As the results are within the limits specified, leave the unit alone, for safety's sake just reflow all the input and output connectors, clean off the flux residue.
Put the lid back on, see how the speakers are protected, and enjoy the music.
If installed remotely in the attic, do something for failure when it occurs.
Probably the best advice right there....😛
It's been playing the first eight studio albums of Led Zeppelin in a loop now for over the past eight hours and I'm not hearing anything that's aurally out of place.
If there's a real problem in the circuitry of this amp it probably would have manifested by now.
Just going to use it as is now since I've only got a $160 invested in total with this amp. The amp was a $55 buy and the new transformer from NAD was $90 plus shipping. If it self destructs at some point I will try to fix it and if I can't I'm not going to be to upset since it's not a huge loss of money.
I do appreciate everybody's contribution here...😉