Nak PA7 clone - Page 2

amplifierguru · 7th September 2005, 02:06 AM

Hi anatech,

It uses a typical (albeit cascoded) diff'l input followed by a high gain Vas and miller comp which kills HF PSRR so it needs clean supplies to sound any good. Class A does that (and linearises the outputs). There are far more elegant ways of achieving the ends without resorting to Class A.

I don't see any surprises here - nothing to hunt one down to audition. It should sound smooth - I guess because it faces none of the hard challenges but sidesteps them with Class A.

This is Sooo characteristic of the monster amps that solve nothing really well and can be easily blown away with a sweet little low bias Class AB 1/10th the size.

I guess what really irks me about such products is that they perpetuate the myth that this is necessary to achieve audio nirvana when all it really does is salve small appendage syndrome or a need for excess, neither of which I believe in.

Cheers,

bra · 7th September 2005, 07:24 AM

here is circuit

bra · 7th September 2005, 07:39 AM

little better

amplifierguru · 7th September 2005, 08:04 AM

Hi Bra,

Are all these parts available in your country? Why would you choose such a dinosaur to copy when it can easily be seen off by inspired Class AB design, a handful of BC546/556 and some everyday output MOSFETs.

It's Kitsch value??

Cheers,
Greg

bra · 7th September 2005, 08:52 AM

I want to use parts from onsemi (samples) if it is possible. It is AB design - idling current is only 40 mA per one transistor.

ocaukrell · 7th September 2005, 08:53 AM

Personally i would love to see the entire service manual (I know someone with a pa7).
Any chance of getting a scan of the whole thing ?.
Will give you my email addy if you like.

This friends PA7 responded very nicley to me replacing al power supply wiring with heaveir gauge.

destroyer X · 7th September 2005, 10:20 AM

hehe.

regards

Carlos

hienrich · 7th September 2005, 11:33 AM

just want to make clear:

is there no global negative feedback fo the said amp?

or is it already the one that is through a trimmer res. from the pre-driver with vbe multiplier
stages?

rgds,

hienrich

carlmart · 7th September 2005, 01:28 PM

Quote:

Originally posted by bra
little better

Can we see where does it go that path going down from the output?

Carlos

bra · 7th September 2005, 02:29 PM

there is no global negative feedback.

7th September 2005, 10:20 AM	#17
destroyer X diyAudio Member Join Date: Feb 2004 Location: Recife - Brasil Northeast	Very interesting...i also here guys.... good to see old friends here. hehe. regards Carlos __________________ Dx Super A - Brazil - Layout Zimmer; http://www.youtube.com/watch?v=yxpYnUA6Bj0

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7th September 2005, 02:06 AM	#11
amplifierguru Account Disabled Join Date: Aug 2004 Location: Earth	Hi anatech, It uses a typical (albeit cascoded) diff'l input followed by a high gain Vas and miller comp which kills HF PSRR so it needs clean supplies to sound any good. Class A does that (and linearises the outputs). There are far more elegant ways of achieving the ends without resorting to Class A. I don't see any surprises here - nothing to hunt one down to audition. It should sound smooth - I guess because it faces none of the hard challenges but sidesteps them with Class A. This is Sooo characteristic of the monster amps that solve nothing really well and can be easily blown away with a sweet little low bias Class AB 1/10th the size. I guess what really irks me about such products is that they perpetuate the myth that this is necessary to achieve audio nirvana when all it really does is salve small appendage syndrome or a need for excess, neither of which I believe in. Cheers,

7th September 2005, 08:04 AM	#14
amplifierguru Account Disabled Join Date: Aug 2004 Location: Earth	Hi Bra, Are all these parts available in your country? Why would you choose such a dinosaur to copy when it can easily be seen off by inspired Class AB design, a handful of BC546/556 and some everyday output MOSFETs. It's Kitsch value?? Cheers, Greg

7th September 2005, 08:52 AM	#15
bra diyAudio Member Join Date: Dec 2002 Location: poland	I want to use parts from onsemi (samples) if it is possible. It is AB design - idling current is only 40 mA per one transistor.

7th September 2005, 08:53 AM	#16
ocaukrell diyAudio Member Join Date: Aug 2005	Personally i would love to see the entire service manual (I know someone with a pa7). Any chance of getting a scan of the whole thing ?. Will give you my email addy if you like. This friends PA7 responded very nicley to me replacing al power supply wiring with heaveir gauge.

7th September 2005, 11:33 AM	#18
hienrich diyAudio Member Join Date: Dec 2004 Location: City of Gentle People	just want to make clear: is there no global negative feedback fo the said amp? or is it already the one that is through a trimmer res. from the pre-driver with vbe multiplier stages? rgds, hienrich

7th September 2005, 02:29 PM	#20
bra diyAudio Member Join Date: Dec 2002 Location: poland	there is no global negative feedback.