Good amp design?

technics · 13th June 2003, 12:53 PM

Hi,

I just found a nice circuit for an amp.
Anyone built this?
Opinions on the design are welcome

Here is the link: http://www.arky.ru/audio/shem/hppa/hppa.htm

raindog · 13th June 2003, 06:35 PM

it looks nice but it also looks very complex. Why dont try the digi-125 from graham dicker. i can send you the files by e-mail if you want.

Andypairo · 13th June 2003, 06:47 PM

As discussed before in these forum, the HPPA by Bert Molenkamp is a good design. I built one for a friend to drive a pair of pro-speakers and it performed very well.

Cheers

Andrea

Tony · 16th June 2003, 11:57 PM

i am not comfortable with a trimpot on the emitters of the input long-tails.....there has to be a better way....

Christer · 17th June 2003, 12:04 AM

Quote:

Originally posted by joan2
i am not comfortable with a trimpot on the emitters of the input long-tails.....there has to be a better way....

There is. Those transistors are so cheap that you can buy
tonloads of them and match them.

It is a bit different for JFETs which vary more and are thus
harde/more costly to match. It is quite common to see a
trimpot in the same location even in well-reputed designs.
Since people always have so much to say about pots and
mostly discuss which is the least bad type, I am surprised
one seldom/never see any discussions on such trimpots.

sam9 · 17th June 2003, 12:53 AM

In input section consisting in the manner of D. Self is simpler. Requires no trim pot and no voltage regulator. A CC source consistind of a small PNP two diodes and a couple of reisitors then. Then a PNP pair to form a differential amp (what you've already got) and you waqnt to go further put a current mirror Two NPN'sbewteen the input pair between the the input pair and the negative rail.

Christer · 17th June 2003, 01:04 AM

Quote:

Originally posted by sam9
In input section consisting in the manner of D. Self is simpler. Requires no trim pot and no voltage regulator. A CC source consistind of a small PNP two diodes and a couple of reisitors then. Then a PNP pair to form a differential amp (what you've already got) and you waqnt to go further put a current mirror Two NPN'sbewteen the input pair between the the input pair and the negative rail.

You mean just dropping the trimpot without replacing it with
two equal-valued degeneration resistors? But then you miss
the benefits of the local feedback in the input stage.

13th June 2003, 12:53 PM	#1
technics diyAudio Member Join Date: May 2003 Location: Burghausen, Bavaria	Good amp design? Hi, I just found a nice circuit for an amp. Anyone built this? Opinions on the design are welcome Here is the link: http://www.arky.ru/audio/shem/hppa/hppa.htm

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13th June 2003, 06:35 PM	#2
raindog diyAudio Member Join Date: May 2003 Location: Timisoara	it looks nice but it also looks very complex. Why dont try the digi-125 from graham dicker. i can send you the files by e-mail if you want.

13th June 2003, 06:47 PM	#3
Andypairo diyAudio Member Join Date: Sep 2002 Location: near Milano , Italy	As discussed before in these forum, the HPPA by Bert Molenkamp is a good design. I built one for a friend to drive a pair of pro-speakers and it performed very well. Cheers Andrea

16th June 2003, 11:57 PM	#4
Tony diyAudio Member Join Date: May 2003 Location: Palatiw, Pasig City	i am not comfortable with a trimpot on the emitters of the input long-tails.....there has to be a better way....

17th June 2003, 12:53 AM	#6
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	In input section consisting in the manner of D. Self is simpler. Requires no trim pot and no voltage regulator. A CC source consistind of a small PNP two diodes and a couple of reisitors then. Then a PNP pair to form a differential amp (what you've already got) and you waqnt to go further put a current mirror Two NPN'sbewteen the input pair between the the input pair and the negative rail.

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