NAD Gainclone repair conversion

[Rick NL]

The NAD 7225 of a friend had its Power-Amps blown up.
As I could not easily find the problem I decided to strip the Output and fit a gainclone instead.
All semiconductors of the Amp section and most of the passive components were taken out. I left some that did not in any circuit anymore and did not use place that I needed.
Also the Zobel and the output coil were kept.

I screwed and a clamped the 3875 on a block of aluminium 8 x 40 x 60 mm, without isolation. First the block and the chip were polished flat with 1200 grid paper on a glass plate. I like a firm contact to a good thermal mass to start with.
This block was fitted to the original heat sink with the use of silicone isolation pad and isolated bushes. I used the original holes of the 3055’s.
I have two 2200uF 50V FC’s near the chip, with two 1uF foil as suggested by the famous application note 202 of Analog Devices. This means one from the negative rail to earth and one from negative to positive rail. None from the positive to earth.
I had some BG coupling caps on order but did not get them and kept the originals bypassed with a 100 nF foil that came out of the old amp.
The result is quite good, better than the original. I am very happy with the result and more important my friend is.
Kind regards, Rick

[Nuuk]

An excellent use of an old, non-working amplifier Rick!

I did the same thing with an old Arcam A60 last year.

And in most cases, it's much easier than repairing the original as well as improving the sound!