Condition when I bought it
Naim Green Logo flickering, One channel plays in considerably lower level than the other.
Inside story…
Output transistor in one channel have been replaced (with BD 911) and also the one ZTX 652 on the driver stage and the MPSA 56 on the current limiter stage also the 0.22Ohn emitters resistors and 4 low power 57 ohms 47 ohms and 100ohms resistors, in other words the channel sucks.
The cause of the flickering display are defective leds. Given the fact that these leds cannot be found anywhere I had decide to replace them with a led luminance panel that works at 4,6V/ 180mA. In order to supply voltage I had use the – voltage rail from the rectifier that supply voltage to the preamp section (practically is not used in the preamplifier) so with a simple circuit that uses a bridge, one 7824 regulator and a Murata Isolated DC converter the display has a separate voltage supply that works fine.
On the power amp board first of all the problem is to find an equivalent transistor given the fact that the original na005 and the equivalent BD 743 simple are vanished and the BD 911 are not working satisfactory.
After many hours of searching I discover the 2N 6487 from ON semiconductors seem OK and these decision finally was proved very efficient.
I had decide also to change both Current limiters transistor (MPSA06/56) and both driver transistor (all of them from Diodes Inc) in order to achieve a better matching.
All the feedback and coupling caps on the preamp were replaced with ELNA Silmics and finally the quiescent current on each channel was adjusted.
The result is a rather pleasant and musical NAIT 3 that after 8 months still works with absolutely no problem.
Naim Green Logo flickering, One channel plays in considerably lower level than the other.
Inside story…
Output transistor in one channel have been replaced (with BD 911) and also the one ZTX 652 on the driver stage and the MPSA 56 on the current limiter stage also the 0.22Ohn emitters resistors and 4 low power 57 ohms 47 ohms and 100ohms resistors, in other words the channel sucks.
The cause of the flickering display are defective leds. Given the fact that these leds cannot be found anywhere I had decide to replace them with a led luminance panel that works at 4,6V/ 180mA. In order to supply voltage I had use the – voltage rail from the rectifier that supply voltage to the preamp section (practically is not used in the preamplifier) so with a simple circuit that uses a bridge, one 7824 regulator and a Murata Isolated DC converter the display has a separate voltage supply that works fine.
On the power amp board first of all the problem is to find an equivalent transistor given the fact that the original na005 and the equivalent BD 743 simple are vanished and the BD 911 are not working satisfactory.
After many hours of searching I discover the 2N 6487 from ON semiconductors seem OK and these decision finally was proved very efficient.
I had decide also to change both Current limiters transistor (MPSA06/56) and both driver transistor (all of them from Diodes Inc) in order to achieve a better matching.
All the feedback and coupling caps on the preamp were replaced with ELNA Silmics and finally the quiescent current on each channel was adjusted.
The result is a rather pleasant and musical NAIT 3 that after 8 months still works with absolutely no problem.
Dear Vagmark,
regarding BD911 in the output stage: what do you mean with "are not working satisfactory" - beside the channel difference was there anything else wrong with them?
...because a significant level difference can hardly be caused by the type of output device in a 0dBV gain current driver output stage...
What else was wrong?
Kind regards
Martin
regarding BD911 in the output stage: what do you mean with "are not working satisfactory" - beside the channel difference was there anything else wrong with them?
...because a significant level difference can hardly be caused by the type of output device in a 0dBV gain current driver output stage...
What else was wrong?
Kind regards
Martin