DC offset on NAD 3120 preamp output

[spandrel]

Spandrel - thanks, you are of course quite correct. I assume I let myself be confused by the switch position shown (closed = power off), but also with all the voltages in that area shown (= power on), that or it's early onset ageing... 🙂

Tell me about it. I recently tested one into a resistive load, connected the meter across one to check the voltage, and promptly blew the amp up. I'd connected both meter leads to the same terminal on the Avo. Oh how I laughed! 😡

I often feel like trying to redesign these old NADs, at least adding delay relays to the pre and power o/p. When the power switch needs changing there's no chance finding a proper replacement so I add a little 24v DC relay to simulate the mute switch, driven from the tx secondary. I haven't tried an AC one, worried about hum pickup. There aren't many places to site the relay on these old amps, especially the horrible power envelope ones.

I'd recommend reseating the o/p transistors, the paste tends to dry out and could lead to failure. It's a messy, fiddly job but I think it's worth it. Meths is good for cleaning off the old paste.

 

[Goldie99]

I know that laugh, well !

Agree completely on the early NADs, I started with a 3020, and still use one often - they're great little amps to learn on, and develop the hands-on skills.
I normally use a completely rebuilt early model, with added protection relays / muting (ESP P33 board). It is a tight fit, but works very well. I also swapped the grease for silicone pads.
I run it integrated, so I've never really considered the pre-amp offset separately until I saw this thread.