amplifier design
Not a very good design.
The differential pairs are simply driven by resistors from the rails. Poor CMRR and if you change the power supply voltage then the currents up the differential pairs will change which will then change the current up the VAS which will then change your idling current which if it is too high will blow up your amplifier.
The trimmer in the bias circuit is dangerous. If the trimmer wiper lifts, you output stage will blow instantly since all bias control will be lost.
There are many good designs on the web. This circuit which you have posted is a classic full complementary design which has been done for over thirty years now.
Not a very good design.
The differential pairs are simply driven by resistors from the rails. Poor CMRR and if you change the power supply voltage then the currents up the differential pairs will change which will then change the current up the VAS which will then change your idling current which if it is too high will blow up your amplifier.
The trimmer in the bias circuit is dangerous. If the trimmer wiper lifts, you output stage will blow instantly since all bias control will be lost.
There are many good designs on the web. This circuit which you have posted is a classic full complementary design which has been done for over thirty years now.
Amplifier design
Dending on your rails, the VAS transistors will not be Ok as far as dissipation is concerned. The pre-drivers (TIP41C/42C) are a very poor choice and are only rated at 100v Vceo so be careull
There are many TO220 driver pairs which are vastly superior to the antiqauted TIP series.
based on your post that you intend to replace the outputs with Tosh 5200/1943, I presume your rail voltages will be in the order of +/- 60 to +/-80v, am I correct?
Dending on your rails, the VAS transistors will not be Ok as far as dissipation is concerned. The pre-drivers (TIP41C/42C) are a very poor choice and are only rated at 100v Vceo so be careull
There are many TO220 driver pairs which are vastly superior to the antiqauted TIP series.
based on your post that you intend to replace the outputs with Tosh 5200/1943, I presume your rail voltages will be in the order of +/- 60 to +/-80v, am I correct?
Sorry, I mistyped, it's +/-70V.
For true RMS 200W on 8ohm at such low as 20Hz and in every condition, using 2*10.000uF per channel I need: sqrt(200*16)+[(200/8)*sqrt2]+6 idle voltage. That means about 70V. My other formula gives the same 70V. So you need a 2*50V trafo.
Let's refer to Phase Linear 400, that produces 2*200W RMS on 8ohm, with +/-75V, with 5600uF caps in the psu.
Regards,
edl
For true RMS 200W on 8ohm at such low as 20Hz and in every condition, using 2*10.000uF per channel I need: sqrt(200*16)+[(200/8)*sqrt2]+6 idle voltage. That means about 70V. My other formula gives the same 70V. So you need a 2*50V trafo.
Let's refer to Phase Linear 400, that produces 2*200W RMS on 8ohm, with +/-75V, with 5600uF caps in the psu.
Regards,
edl
BlackMTX said:
Hmm, that doesn't look like a very stable design - there are improvements over the 1st schematic, in terms of power-supply decoupling of the input stages and constant-current source for their emitters; output SOA limiting - yet the input pair isn't balanced, the VAS is running wide open (save for an RC to one supply rail), rather lowish FB corner (330pF || 10K).
Cheers!
4mhz low for you?
that circuit is a definite improvement over his first one. let me qualify, the input and vas are on lowers rails and that is because the output stage has been designed with voltage gain on it. reminds me on the "Tigersaurus" of Daniel Meyer from SWTP in the circa 70's. i have built several of this amps using original transistors, while the bass packs a lot of puch, the mids and highs are barely tolerable! but yes it delivered lots of power! i was using just a pair of 10,000uf/100volt rail caps on 75volt rails.
power traffos were of 2inch center leg stacked to 3inches and sagged very little even when testing both channels at full power.
why don't you see the super leach if you wat to run output rails at +/-85?
Hi Tony - I did say "there are improvements".
" reminds me on the "Tigersaurus" of Daniel Meyer from SWTP in the circa 70's."
Yes, and that's exactly the same amplifier that gave several people headaches due to its instability. Your experience may be different, given your excellent background! Its exactly the output stage with gain that causes problems - its so easy to get the thing to oscillate, any inductance in the high-powered feedback resistors (R44, R45) already causes the amplifier to ring.
Cheers!
Clem
ps: 330pF and 10K, yes, lowish.
" reminds me on the "Tigersaurus" of Daniel Meyer from SWTP in the circa 70's."
Yes, and that's exactly the same amplifier that gave several people headaches due to its instability. Your experience may be different, given your excellent background! Its exactly the output stage with gain that causes problems - its so easy to get the thing to oscillate, any inductance in the high-powered feedback resistors (R44, R45) already causes the amplifier to ring.
Cheers!
Clem
ps: 330pF and 10K, yes, lowish.
Hi clem,
i still have several boards with me! but i dismatled and re-used the parts on something else. this is one amp that is easy to forget, and glad to get rid of.
the Bryston amps are of the same topology although lower gain on the output stage.
i still say the Leach Super Amp is hard to beat in the 250watt class of class AB amps. well thought out design, and the best part of all is that it is free!
i still have several boards with me!
but i dismatled and re-used the parts on something else. this is one amp that is easy to forget, and glad to get rid of.the Bryston amps are of the same topology although lower gain on the output stage.
i still say the Leach Super Amp is hard to beat in the 250watt class of class AB amps. well thought out design, and the best part of all is that it is free!
i have this design and my power supply is higher than the supply of this design..so i
hi Clovi,
I'd already built that P400 design a last decemder 2005 with some modifications. I used 2x50Vac trafo.
In that amplifier, i'd change R4,5 to 150 ohms. Q1,2,3,4 to MPSA92 and MPSA42.
And in the VAS section af the circuit, I'd change Q5,7 to TIP41C and TIP42C. In the driver stage, I also change Q10,11 to A1516 and C3907. And lastly in the output stage i used 2SC2922 and 2SA1516, which is twice per rail, and four in all both NPN & PNP.
My amplifier sounds good until now with my 4 unit of 15" speaker 300W.
Dont forget to put the bias transistor near the heatsink.
Sooner ill add another output devices so that i can load 2ohms.
any comments from other members are welcome, coz im not that too expert.
GOD BLESS......... 
hi Clovi,
I'd already built that P400 design a last decemder 2005 with some modifications. I used 2x50Vac trafo.
In that amplifier, i'd change R4,5 to 150 ohms. Q1,2,3,4 to MPSA92 and MPSA42.
And in the VAS section af the circuit, I'd change Q5,7 to TIP41C and TIP42C. In the driver stage, I also change Q10,11 to A1516 and C3907. And lastly in the output stage i used 2SC2922 and 2SA1516, which is twice per rail, and four in all both NPN & PNP.
My amplifier sounds good until now with my 4 unit of 15" speaker 300W.
Dont forget to put the bias transistor near the heatsink.
Sooner ill add another output devices so that i can load 2ohms.
any comments from other members are welcome, coz im not that too expert.
GOD BLESS.........
jcatiwalaan said:ton,
the transformer i used is 50-0-50 20Ampere. And 20,000 uf per/rail. Is this owkie?
I'll try to substitute mje340 and mje350.
Thanks.........
in paper it looks ok, but judging from the very optimistic attitude of winders in our country, one can never tell, unlless you can give me details of the transformer iron, then i can be able to tell you how is it.
good job though, are you into mobile disco kind of thing?
tony
there are threads running here about leach amps:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=51392
and another:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=52459
there are lots of thread about leach amps posted here, just use the search function to locate them.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=51392
and another:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=52459
there are lots of thread about leach amps posted here, just use the search function to locate them.
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