Expert: Cleggsan - 8/23/2009

Question
I have an NAD 2200PE Amplifier. This amplifier has seen lots of maximum level play in the past, but recently has started having problems at lower levels (when the loudness button on the NAD preamp is pushed in, and the volume knob is set at about 1/3 or less) where the sound in the right and/or left channels cuts out for as short as half a second and as long as about 10 minutes at a time. However, after a period of playing the amplifier loud, it can frequently be played quietly without a problem (but not always). I have tested the preamp and source with other equipment and narrowed the problem down to the amplifier. What can I do to fix this?

Answer
It is a fine amplifier and well worth getting it restored to normal operating condition.

The output transistors have a heat transfer silicon grease in between the transistor and the heat sink they are mounted on.   This grease dries out over a few years and the heat transfer is diminished causing the transistors to heat up and kick in the protection cutouts.  The reason it is better when you have played at loud levels is because class AB amps get less heat into the outputs at loud levels than at middle levels.  So, playing it loudly will actually help cool down the output transistors a little bit. The worst for heat dissipation in the output is when the audio is running at 1/3 to 1/2 power.

In any event, it is a tedious task, but the cure is to remove the power transistors and regrease the mica washers between the transistors and the heat sink they are mounted on.  A good technician will take an hour or so to complete it.  An novice will take 3 or 4 hours to do it - and maybe make a permanent mess out of it!

All the best,
C