Hey!
I replaced R317 after the due diligence process with cotton swabs and IPA. And guess what, it has played music for about an hour now!
Readings are good except for 17 V is 16 something volts, could that be the missing muting caps? I thought I'd order fresh ones to solder in.
It sounds fine without them, but pressing "mute" didn't do much of course... There is still something wrong with the front media player input, now it doesn't even switch to that input when a 3.5 mm plug is inserted, but who cares? I managed to restore a perfectly good amp and CD player found in the trash to something that plays great on my Dali 505's that I bought on swedish "Craigs list" for USD 60 (or 74 Canadian dollars - thanks anatech/Chris!!!)... With minimal electronics skills and my first soldering project.
The bias current is steady. DC at the outputs is like 5-10 mV. Life is good!
Thanks diyaudio forum and Chris!
/Daniel
I replaced R317 after the due diligence process with cotton swabs and IPA. And guess what, it has played music for about an hour now!
Readings are good except for 17 V is 16 something volts, could that be the missing muting caps? I thought I'd order fresh ones to solder in.
It sounds fine without them, but pressing "mute" didn't do much of course... There is still something wrong with the front media player input, now it doesn't even switch to that input when a 3.5 mm plug is inserted, but who cares? I managed to restore a perfectly good amp and CD player found in the trash to something that plays great on my Dali 505's that I bought on swedish "Craigs list" for USD 60 (or 74 Canadian dollars - thanks anatech/Chris!!!)... With minimal electronics skills and my first soldering project.
The bias current is steady. DC at the outputs is like 5-10 mV. Life is good!
Thanks diyaudio forum and Chris!
/Daniel
I learned a lot doing this with the aid from here. And it was fun. Thanks a lot! Next up might be recapping this beauty:
Have nice one!
/Daniel
An externally hosted image should be here but it was not working when we last tested it.
Have nice one!
/Daniel
Hi Daniel,
The 16.xx volts is fine for the 17 volt power supply. That is normal tolerance and doesn't matter one bit, so smile and enjoy the music.
As soon as you reported the supply voltages, the answer was clear if we were looking at a single fault. The negative supply uses the positive as a reference to track. So when your +17 volts was lost, the negative supply also dropped out. Without power, the op amps used to correct DC offset were unable to do their job, and so the DC offset hit the trigger point for your protection circuit.
Most designs use the DC servo as a "nice" way to reduce DC offsets from maybe 200 mV or so down to the nice 1-5 mV we are used to seeing. In the NAD design, the DC servo is a required part of the circuit. Without them, the DC offset would rise to an unpleasant level, maybe a volt or more. That would cause a thump in your speakers when turning it off. By including the protection circuit (should be mandated by law), the natural action of the amplifier circuit would trip protection, so they had to do something about the DC offset.
Your muting transistors are probably okay. They can be tough to find, so maybe just put the old ones back in. If you are up to it, you can use a relay instead of the transistors. That will take some design on your part, so don't drop everything and rush to install a relay.
-Chris.
The 16.xx volts is fine for the 17 volt power supply. That is normal tolerance and doesn't matter one bit, so smile and enjoy the music.
As soon as you reported the supply voltages, the answer was clear if we were looking at a single fault. The negative supply uses the positive as a reference to track. So when your +17 volts was lost, the negative supply also dropped out. Without power, the op amps used to correct DC offset were unable to do their job, and so the DC offset hit the trigger point for your protection circuit.
Most designs use the DC servo as a "nice" way to reduce DC offsets from maybe 200 mV or so down to the nice 1-5 mV we are used to seeing. In the NAD design, the DC servo is a required part of the circuit. Without them, the DC offset would rise to an unpleasant level, maybe a volt or more. That would cause a thump in your speakers when turning it off. By including the protection circuit (should be mandated by law), the natural action of the amplifier circuit would trip protection, so they had to do something about the DC offset.
Your muting transistors are probably okay. They can be tough to find, so maybe just put the old ones back in. If you are up to it, you can use a relay instead of the transistors. That will take some design on your part, so don't drop everything and rush to install a relay.
-Chris.
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