NAP180 Wiring Question

[MJS]

The 180 shares its chassis with the 250. The amp boards went where they fitted in the 250, as did the transformer. But don't ask me why we have long wires from the transformer to the rectifiers and smoothing, the power supply board would be better off next to the transformer where the large caps in the 250 would sit.

Les probably kept the trip in the chassis for use with the new parts. Although I do have to question why ripping every single item out of the chassis and replacing it but still having Naim on the front is ok.

 

[Suffolk Tony]

I finally got round to installing everything in a spare enclosure. Copied the layout of a 180, wired as per that amp, but there's a mains buzz from both channels, even without a source connected. Any idea where to look please folks?

 

[MJS]

Short the inputs to ground then test with a scope attached, you really don't want speakers on it. There should be absolutely no connection between chassis earth and signal ground. Watching the noise on the scope you should be able to see if touching the loom or moving it changes the level and shape. You're looking for a noisy sawtooth waveform of a mV or so at most.

 

[Suffolk Tony]

Thanks MJS. Only using an old pair of computer speakers for testing. Sorry, haven't got a scope, but I'll double-check for the grounding issue.

 

[Jeff Young]

Post some pictures. You might have a ground loop....

 

[MJS]

You really do need even the basic rudimentary test equipment like a scope, even if you are taking what's, in effect, the middle of an amp out of a box and transplanting it. The number of things that can be wrong are all potentially speaker-frying.

 

[Suffolk Tony]

You really do need even the basic rudimentary test equipment like a scope, even if you are taking what's, in effect, the middle of an amp out of a box and transplanting it. The number of things that can be wrong are all potentially speaker-frying.

Probably if I was doing lots of this stuff. But I've gotten by scopeless for many years, and built many things successfully without. More of an occasional interest...

A nice chap in Chesterfield's helped. There are these two purple wires that don't go anywhere, but if you hold them - the noise stops!