Buffer Power amp. - Page 3

K-amps · 22nd September 2008, 08:38 PM

Thanks PMA.

What values do u suggest for 95vdc rails.

I might now be able to do class A with that unless u are referring to the preceeding stages..

C+ and C- is that mean a CCS inserted there?

Wavebourn · 22nd September 2008, 08:58 PM

Here is mine, I used it about 25 years ago as an output stage in hybrid amp. Actually, it is a complementary opamp with an unity gain. I used diodes D1 and D4 instead of transistors in diffpairs because no transistors can survive reverse BE voltage when output is shorted. I used it as a fast fix of a vacuum tube guitar amp (Hungarian BEAG) when no replacement output transformer was available (couple of such stages as a bridge to drive 32 Ohm speaker cab). The owner decided to leave it as is, with no output tubes. Probably, it was the first hybrid amp then, though not commercially available...
As drawn, it is class AB, for class A remove diodes D2 and D3 together with pots and resistors to ground.

Edit: transistors were KT814/KT815 and KT818/KT819.

forr · 22nd September 2008, 09:26 PM

"a HEC follower circuit"

Jan Didden's Pax amplifier output stage is a good candidate, more linear than a class A buffer, I think.

turnA_zpoint · 22nd September 2008, 10:19 PM

Hi
Though I don't test 95V supply....Sorry,
they are some bias for buffer circuit (not main loop feed back).
(It is not designed for 95V supply,so must replace other Tr.)
It's bias with local feedback.

If I test 95V supply , I may be try below ,
(because needs over 190V spec)

Power :2ＳＪ201/2ＳＫ1530 200V/12A/150W　
other all :2SA1406/2SC3600 200Ｖ/200mA//1.2W

if the supply is under 90V , I may try
:2SA1208/2SC2910 180V/70mA/0.9W

and resister 5K ohm is may be change (may be) 25K ohm.

OR chip amp LME49811,LME49830 ,not discrete

If I mistake ,I'm sorry very much ,please point out.

Regard

K-amps · 22nd September 2008, 10:30 PM

Thanks for the additional thoughts and parts values. I think this needs to be vetted out some more. Also I plan to use BJT's in the Output namely NJW1302 and 3281 (260v parts)

CBS240 · 23rd September 2008, 05:40 AM

Quote:

Originally posted by forr
"a HEC follower circuit"

Jan Didden's Pax amplifier output stage is a good candidate, more linear than a class A buffer, I think.

Hi

I have one I have been playing with, I will post a schematic sketch when I get home tomorrow evening.

I am working out of town for a day or so.

bra · 23rd September 2008, 02:15 PM

ARC

bra · 23rd September 2008, 02:34 PM

Q1-4 ( MJ 15015/16 )
Q9-20 ( MJ15003/4 )

bra · 23rd September 2008, 02:38 PM

Q1-Q4 2SB697/2SD733

K-amps · 23rd September 2008, 05:43 PM

Thanks Bra... What is Q1 & 4 doing?

What values do I use for +/-95v rails for the resistors?

22nd September 2008, 08:58 PM	#22
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	Here is mine, I used it about 25 years ago as an output stage in hybrid amp. Actually, it is a complementary opamp with an unity gain. I used diodes D1 and D4 instead of transistors in diffpairs because no transistors can survive reverse BE voltage when output is shorted. I used it as a fast fix of a vacuum tube guitar amp (Hungarian BEAG) when no replacement output transformer was available (couple of such stages as a bridge to drive 32 Ohm speaker cab). The owner decided to leave it as is, with no output tubes. Probably, it was the first hybrid amp then, though not commercially available... As drawn, it is class AB, for class A remove diodes D2 and D3 together with pots and resistors to ground. Edit: transistors were KT814/KT815 and KT818/KT819. __________________ If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.

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22nd September 2008, 08:38 PM	#21
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	Thanks PMA. What values do u suggest for 95vdc rails. I might now be able to do class A with that unless u are referring to the preceeding stages.. C+ and C- is that mean a CCS inserted there?

22nd September 2008, 09:26 PM	#23
forr diyAudio Member Join Date: Dec 2004 Location: Next door	"a HEC follower circuit" Jan Didden's Pax amplifier output stage is a good candidate, more linear than a class A buffer, I think.

22nd September 2008, 10:30 PM	#25
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	Thanks for the additional thoughts and parts values. I think this needs to be vetted out some more. Also I plan to use BJT's in the Output namely NJW1302 and 3281 (260v parts)

23rd September 2008, 02:34 PM	#28
bra diyAudio Member Join Date: Dec 2002 Location: poland	Q1-4 ( MJ 15015/16 ) Q9-20 ( MJ15003/4 )

23rd September 2008, 02:38 PM	#29
bra diyAudio Member Join Date: Dec 2002 Location: poland	Q1-Q4 2SB697/2SD733

23rd September 2008, 05:43 PM	#30
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	Thanks Bra... What is Q1 & 4 doing? What values do I use for +/-95v rails for the resistors?