Power amp under development

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#3,861
anyone up to matching a few mpsa56/mpsa06...

Subject says it plus I'm short on time/equipment/expertise to do same to repair 2 amps.
Both w/DC offset problems one 33mV/77mV, the other 150mV/1V!

I plan to provide 50 pieces of each, purchase pending, pay shipping both ways, plus what your time is worth to ya. My PP account is ready.

I can include schematic or for your perusal click on...

http://www.diyaudio.com/forums/solid-state/177067-will-pay-belles-1-series-amp-info-schematic-4.html

Per schematic of this dual differential, each channel needs 3 each mpsa56/mpsa06.

I hope to come out of this w/ 2 spare sets for future repairs to two amps as I have 3 of these amps; the third w/out issues for the moment.

thanks in advance, Tony
 
#3,868
Hi,
I have built one nmos350 mk2, on the pcb available (nmos350) modifyed "on the fly". I have put only 4 mos-fet (it's enough power for me).
I have a couple of question for QUASI:
- the pcb board of mk2 is available?
- in the first setup of bias current I have only 1V (with 100 ohm resistors) instead of 8V required.
Thank a lot for the reply.
 
#3,870
Thanks AndrewT,
- I have measured the total current of circuit (how is described in construction guide doc
An externally hosted image should be here but it was not working when we last tested it.
) across the 100 ohm resistor put instead of fuse on the positive rail (+ 69 V);
- I discovered that have - 69 V on the output rail;
- T2 it's a little bit too hot, but across R4 I don't have any absorbtion (0 mV);
- the schematic:
An externally hosted image should be here but it was not working when we last tested it.
 
#3,872
do not measure the total amplifier current across a 100r resistor.

That method incurs a voltage drop on the supply rail and thus affects amplifier performance.

Put the fuses back in. Remove the bulb tester and power up.
Measure output bias across the output source resistors.
 
#3,875
updated:
I had made an error in the connection of R12: I connected to the collector of T7 (the red LED (LED 1) would not turn on and I had no absorption in the differential in VAS and in the driver.
Restored to the right connection of R12 to the base of T7 absorptions are returned to the correct values ​​EXCEPT that measured at the terminals of R22 (driver stage) that is approximately 1V instead of 3.96 V (0.018 V / 220 ohm). Furthermore, the bias current (VR2) is not moved by approximately 2V.
 
#3,877
#3,880
Wait a moment, Andrew.... perhaps i found a solution for the photos.... I try....
43331-power-amp-under-development-340.html

parasitic_oscillation.jpg
[/url][/IMG]
IMAG0269.jpg
[/IMG]
Note that parasiticoscilation it's not present without loudspeaker connected.
I hope my photos can viewable.....
 
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