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Hello! I'm a newbie to this board, but Google searches reveal good knowledge here, so I'm gonna ask.
Yesterday I bought a NAD 3155 off Craigslist -- it was a good price and when I first got it wired up, it sounded fantastic. I listened to it for a few hours yesterday.
Today when I listened to it, it cut out after about 10 minutes. It continued playing at very low volume, and the volume knob had no effect. Turning it off and back on allows it to work again, for about 10 minutes.
This happens even when listening on headphones, so the problem seems to be in the pre amp.
Perhaps related: when I listen to my turntable, I get an increasingly loud hum, even with the ground wire connected.
I'm far from an electronics expert but this amp was inexpensive enough that I would be happy learning on it. Any recommendations on things I should check first?
Follow Ups:
Disconnect everything and see if it still does that.
Sounds like a defective circuit.
charles
I disconnected the bridge between the pre and and the power amp, connected my D/A converter directly to the power amp in, and listened through headphones. In that state, it works indefinitely. So it definitely seems like it's in the pre-amp after all.
Any hints on how to find a defective circuit? (I'm a complete newbie at this)
Thanks for all your help so far, I'm realizing a lot of what I thought I knew was totally wrong!
Look at my other post.
I suggested connecting a DIFFERENT source thru a different input.
NAD phono input transistors CAN be a little fragile and all you need to do to mess one up is connect or DISconnect with power on. That huge POP is the transistor getting a huge jolt.
Too much is never enough
Welcome! sounds like one of the circuits.
First thing I'D do is disconnect the TT and find another source. ANY source will do as long as it's not thru the lowest level inputs on the amp.
Unplugging an RCA while the TT is still plugged in will or CAN really ZAP the input transistors in the first gain stage. The amp must be OFF before connecting stuff. That is 'best practices' and helps keep you out of the fix-it shop.Also, how HOT is the unit getting before it cuts out? Any front panel indication like the soft clip or other lights?
Keep the amp OUT in the OPEN for these tests. Cooling air is critical. If it runs TOO WARM, that's a problem. Maybe bias is adjusted too high. Not likely in an un-messed with unit.Pulled the cover yet and smelled around for BURNED anything? Does it look like any repairs were made? Stuff like a giant blob of heat sink compound (usually white) sticking out from under ONE output transistor would be a great clue and nearly a 'smoking gun' of previous abuse and marginal repair.
Too much is never enough
Edits: 11/17/14
And I *loved* that amp! I was running it in bridged mode and it could really put out some power. One thing to check is to see if you have the Soft Clipping circuit engaged. There should be a button on the back of the unit for this. Try changing it from its current setting and see if that solves your problem....
Good luck!
-RW-
I thought of that! I tried engaging it & disengaging it with no effect, unfortunately. Thanks though! And it does sound REALLY good. Until it doesn't :)
It sounds like the protection circuits are kicking in. How did you verify that the headphones are working off the preamp and not the amp section of the NAD?
Maybe it is the protection circuits. I assumed the headphone out was coming from the pre for no good reason other than I thought it made sense -- it didn't even occur to me that it could be coming from the power amp.
I am not familiar with your amp. Is there a way to disconnect the preamp section from the power amp? If there is do it and see if your headphones work,if they do then you will know that the headphones work off the preamp.
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