dc offset for nakamichi amplifier 1

reddish75 · 6th January 2007, 01:36 AM

does anyone know the idle current, and the dc offset settings for this amp, i have just repaired it (right channel had blown causing a fuse to blow on the ac primary) but now i think that the pots have gone because measuring the offset one side is 50v and the other is 35v, and its still in protection mode.

can anyone help as i cannot find any information manuals about this amp, ive even tried nakamichi!

thanks chris

Extreme_Boky · 7th January 2007, 06:47 AM

You're in the wrong forum... Try analog forum.
To get you started, offset pot is near input differential transistor pair (it could be 5-pin matched and thermally coupled on the same die “single” transistor).

The bias pot should be near drive / output transistors.

These two pots can be used to FINE (!!!) tune settings for no more than 20-30mV DC offset and about 50-100mA idle current; you obviously have the case of shorted transistors in the output / drive stage because your output is sitting at +Vcc (!) Sometimes, the output could go this high if you have a faulty input differential pair...

Yes, check that you have both halves of the power supply rails okay (plus AND MINUS 50V).

Good luck,
Boky

6th January 2007, 01:36 AM	#1
reddish75 diyAudio Member Join Date: Aug 2006	dc offset for nakamichi amplifier 1 does anyone know the idle current, and the dc offset settings for this amp, i have just repaired it (right channel had blown causing a fuse to blow on the ac primary) but now i think that the pots have gone because measuring the offset one side is 50v and the other is 35v, and its still in protection mode. can anyone help as i cannot find any information manuals about this amp, ive even tried nakamichi! thanks chris

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7th January 2007, 06:47 AM	#2
Extreme_Boky diyAudio Member Join Date: Dec 2003 Location: Sydney	You're in the wrong forum... Try analog forum. To get you started, offset pot is near input differential transistor pair (it could be 5-pin matched and thermally coupled on the same die “single” transistor). The bias pot should be near drive / output transistors. These two pots can be used to FINE (!!!) tune settings for no more than 20-30mV DC offset and about 50-100mA idle current; you obviously have the case of shorted transistors in the output / drive stage because your output is sitting at +Vcc (!) Sometimes, the output could go this high if you have a faulty input differential pair... Yes, check that you have both halves of the power supply rails okay (plus AND MINUS 50V). Good luck, Boky

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