Fairly basic beastie - not vastly removed from the old Linsley Hood. The particular specimen on my bench sometimes works fine and sometimes flips the output to -38VDC.
This is not conducive to long speaker life. No amount of heating/cooling semiconductors seems to trigger the problem.
Q: Anyone met this and one and nailed it?.
This is not conducive to long speaker life. No amount of heating/cooling semiconductors seems to trigger the problem.
Q: Anyone met this and one and nailed it?.
Have you put an oscilloscope probe on the output? I suspect it may be oscillating now and then...
Some photos of the pcb would be useful to see if it is original or not and would be a good start.
@caowei and @Oleg Turbin are the most documented and competent in terms of Naim of this generation, they are the only ones that I know capable of producing exact clones of this generation .
Good day
Dear mobyd
Your nap120 use the original tantalum caps ? Without recapping on all time ?
I think you need make the replacement work with old tant caps on yours NAP120 boards
47uf tantalum in feedback is very old and fail on some time. After that you have minus power on output.
Also if we have the damage one pins of BC239 transistors. Amplifier is stay with -38v on all time. But we not see this
p.s
just in case, measure the base-emitter voltage on all transistors on the working board and on the board with the problem.
If you're lucky, at the moment a constant voltage appears on the faulty board, you also need to measure the base-emitter voltage of the BC239 input stage suddenly, indeed, one of the transistors periodically falls off the base pin.
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