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Vivek 14th August 2002 09:00 AM

Another amp
Check out this amp at and let me know your comments.
There was a 120 W amp featured in Elektor sometime ago. It used BDX 66/67 for the output stage. Does anyone have the article of that amp and is it worth trying? I think the schematic was posted in this forum somewhere but I could not locate it.


Vivek 14th August 2002 04:07 PM

Someone tell me something please.


Dozuki 15th August 2002 03:14 AM

The schematic looks sound on quick glance. Fairly straightforward design with classic topology. since this seems to be a compilation of ideas from different sources I might consider adding a current mirror to the LTP. If you use a ccs in the LTP and VAS, might as well.


Vivek 15th August 2002 04:05 AM



yugaaa 15th August 2002 05:00 AM

this amp works well. i have been using this amp substituting with tip142 147 transistors.the original output devices are costly.

Vivek 15th August 2002 07:29 AM

Hi Yugaa,
I suppose you mean the Elektor amp. How does it sound?


djk 15th August 2002 08:30 AM

Put a resistor in series with the base of the current source for the second voltage amp, 470R would be a good place to start. Improves recovery from clipping. The 1N4007 in the limiter circuit should be fast diodes, try the 1N4935. Flyback diodes across the outputs are cheap insurance, 1N4935. A pair of power supply bypass caps in the range of 22F~47F at 63V would make the bass seem more solid. Input cap to be a film type. Feedback cap to be non-polar or back-to-back electrolytics with a small film bypass. The diode across this cap should be increased to two in series, and then two more in opposite polarity. The poles are staggered wrong, supply is 1hz (4R), feedback is 9.6hz, input is 3.3hz. Change feedback cap to 470F, 4.5hz. Change input cap to 1F, 7.2hz. Input pole must predominate, feedback pole must be between input and power supply poles. If not staggered properly amplifier will ring at infrasonic frequencies when clipped, very hard on woofers and very poor sound quality. I would also consider doubling the current in the second voltage amp, you could be running out of drive current at low impedance. Looks very nice!

Vivek 15th August 2002 02:30 PM

Hi djk,
Thanks for the tips. But I assume you are talking about the amp in the link I have posted.


marcus66 16th August 2002 12:27 PM

Hi all,

I was just notified that my amp (called M250)
was being discussed here. Thanks to Djk for the detailed comments.
If you would like to try my design
I think that you should take djk's suggestions
into consideration. I will try these changes myself as soon as I find the time. I have
added FR diodes at the output in my amp, but
regrettably I have had too little time
recently to update the page.

Best Wishes,


marcus66 13th September 2002 11:52 AM

I have updated the M250 amp design (as well as my prototype). Please re-visit the URL posted at the top of this thread for the
new schematic. Thanks again to Djk, whose
comments have now been put to use.

Best Wishes,


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