Cutting the etch on the pcb is the way to go. Cutting away unused etch isn't strictly necessary as any stray capacitance will be negligible. I mounted 5W emitter resistors on the heatsink and stranded wire to hook everything up. On my unit there's speaker selector switches and a bunch of wiring between the output pair and the terminals on the back of the chassis. so the few extra inches of wiring isn't going to make any difference.
mightydub said:
Mine is PCB trace directly to speaker terminal, better sound quality I guess?
I cut away the unused parts since I was cutting and thought "might as well", and it serves as a safety measure just in case a cut decided to reconnect itself.
An externally hosted image should be here but it was not working when we last tested it.
This is the trace that I see at the bottom of the PCB (red being a cut), my original plan was as shown with the resistor mounted under the PCB. Pretty straightforward.
I thought a 3W (i used 3W in this case) resistor would mean that it can handle 3W without overheating itself? Shed me some light?
Oh and, between the emittor output and the speaker terminal there is this rectangular black box that is standing up (symbol at top left corner). What is it?
wwenze said:
simpler and cheaper to manufacture is my guess.
figure out the maximum current (RMS) through the resistor and calculate power dissipation (I^2R), apply whatever de-rating factor makes you happy.
That's a self resetting circuit breaker intended to prevent overload. Leave it in if you want the protection, replace it with a jumper if you are concerned about it degrading the sound.
Many thanks to those who have replied, the amp is working now. 
At least that's what I'd hoped. The amp is now of working condition but there's this loud humming and lack of bass in both channels and without any input, and the preamp is very soft. At least it doesn't blow up anymore.
If I'm lucky it might just be as simple as the steel cover getting attracted to the transformer and causing grounding problems (I actually heard the steel cover move when I switched on the power, yea I didn't screw it on yet). Worse case scenario (guessing from the soft preamp) the power supply is bad, or all the caps need to be changed (it's hard to tell which is bad because all look good).
I'll play with a few switches and take some measurements when I return home. At the very least, the first problem at hand is solved. Thanks everyone.
At least that's what I'd hoped. The amp is now of working condition but there's this loud humming and lack of bass in both channels and without any input, and the preamp is very soft. At least it doesn't blow up anymore.
If I'm lucky it might just be as simple as the steel cover getting attracted to the transformer and causing grounding problems (I actually heard the steel cover move when I switched on the power, yea I didn't screw it on yet). Worse case scenario (guessing from the soft preamp) the power supply is bad, or all the caps need to be changed (it's hard to tell which is bad because all look good).
I'll play with a few switches and take some measurements when I return home. At the very least, the first problem at hand is solved. Thanks everyone.
i worked at NAD for a while. i seem to remember the 3020 had a modification to cure oscillation. i lost my NAD notebook a long time ago, so i don't even know what color the modification dots are supposed to be (there are colored dot stickers next to the serial number on the back of the unit if it's had factory modifications done to it).
analog_sa said:
Lack of bass without any input is quite normal
Did you set correct bias? Offset?
You should be able to find out if it's the preamp section resposible for the hum by just removing the links.
Haha, perhaps some grammar problem there.
Lack of bass when there is input and humming sound both with and without input.
I checked the preamp section to be working perfectly. Hence so should the regulated power supply.
DC offset at both speaker outputs is ~20mV.
Biasing... I don't know how to set.
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