The famous George rang.
My NAD's developed a nasty hum, can you have a look?
Yeah, why not...
A particular favourite of mine. These must have been one of the best selling amps throughout it's life...
(There's even a wikipedia article on it here.)
Now, many of these are getting a bit long in the tooth now.... and George's is no exception.
I switch it on, and there's some awful humming which just won't go away. Some of these amps suffer with a hum on switch on, which disappears after a few seconds, after frightening the user. We'll come back to that later.
One feature of this amp is the shelf at the back, where all the connections are located. Makes access easy if you're fishing around around the back. It's not without it's issues, however...
Turn the amplifier upside down, and remove the base plate (8 screws, short one's in the middle!)
This is the underside of the connection "shelf" ... dry and broken joints are normal here, so solder the lot up...
There's some caps showing signs of their age, and have failed. I'm going to change the usual suspects..
... as well as the four main smoothing caps.
... and the other screw securing it on the back
and the other towards the rear ...
You can now remove the brace bar to access the whole of the PCB.
..things are much improved, but there's another fault... I mentioned it earlier. When you initially switch the amp on, there's a very unpleasant hum which decays, leaving the amplifier performing ok.. it's like a "whomp" as it turns on. It's a very common fault...
It's caused by this capacitor (and sometime's its neighbour too). I change them both for 47uF 63v types... whomp gone!
Bias is checked , and is spot on. Just got to button it up, and give it a good testing with "The Lasters" by Fred Deakin.
Hi Doz.
ReplyDeleteHope you are doing good. Came back to your blog to read some updates. Yet to replace those cap in my Nad310. (If u recall me replying to your nad310 post)
Got some insight from reading this post regarding the hum during power up. Im still waiting for the local
supplier to restock the huge capacitor.