So, youre sitting there listening to music and all of a sudden your amp clicks out, the power light goes red, and theres no music. ‘Shit. Its broken’, you think. Power off/on? Same thing.. Once it cools down, it powers up, but it clicks out again after 10 or 15 minutes of use.

Well if you found me by the google because precisely this happened to you, you’re in luck. I just repaired mine for the wonderful sum of 63 cents. Anyway, let’s move on.

To perform this fix you need to be somewhat comfortable with a soldering iron, and be willing to take your amp apart. If you aren’t very good with an iron, you’ll want to read through some how-to pages elsewhere until you’re comfortable with replacing capacitors on a printed circuit board.

My C370 ripped apart on my workbench

So it turns out the problem with the design is that NAD decided to put a hot-running diode right beside (touching!) some electrolytic capacitors. This dries out the caps, which changes their values. When their values change, the protection circuit goes all wonkey.

The protection circuit

First of all, locate the protection circuit pictured above. As you can see from the picture, mine had some obvious heat problems. Nothing looks broken per se, but it looks nicely toasted, especially on the right side and top. To get it working again, I’d reccomend replacing the three topmost capacitors. Their values are 4.7uF, 47uF and 10uF all rated at 50V. I wouldn’t get anything larger than 50V as I’m not sure if it would fit.

**edit: According to Stu in the comments below, some amps have 63V caps, so I guess slightly larger caps might fit. Either way I wouldn’t recommend replacing your capacitors with new ones of a lower value than stock**

For those who are interested, here is the schematic for the protection circuit:

NAD C370 Protection Circuit Schematic

With those three caps replaced, the amp should work fine. But in a couple years, those caps will die too. I found a great solution on a forum: move the diode to the other side of the board. Watch the polarity!

Diode on the back of the board

Now apply power, hope there aren’t any sparks, and enjoy the music!

This weekend I rigged up a jacob’s ladder from an old microwave oven transformer. Due to the low voltage (~2kV) it won’t self start. You can see me starting it with a paperclip on the end of a paint stirring stick. Although the voltage is a bit low, these transformers can put out huge current, so the arc is great once it starts.

Playing around with it earlier, I got arcs as long as 10″ from it. Now the search is on for another MOT or perhaps an old neon sign transformer.

I just put up a website for the Ryerson Hobby Electronics Club.

Not much point, really.  Just linking it so the googlebot checks it out.

1. create weblog

2. dont tell anyone where it is

3. …..

4. profit!!