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Old 2nd April 2013, 08:40 AM   #8761
fas42 is offline fas42  Australia
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Quote:
Originally Posted by mjona View Post
The late John Linsley-Hood is one who has defined the problems you refer to - most recently in his book "Valve&Transistor Audio Amplifiers".
Thanks for the pointer ...
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Old 2nd April 2013, 10:01 AM   #8762
dvv is offline dvv  Serbia
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Originally Posted by PlasticIsGood View Post
Best thing about the book is that it's a story. Especially for a novice, seeing how a circuit works isn't the same as knowing why it's used, which is generally a matter of history.

It's probably a very English history, and partisan in several respects, but illuminating all the same. Not up to date though, obviously.

If I remember his story, life was a struggle for transistor power output stages until reasonably matched NPN, PNP pairs became available. Can't much remember why...problem of symmetrical drive for PP I guess.
Very, very British.

There are quite a few British audio companies which used quasi-complementary output stages way after more than enough complementary devices was available. Naim, Arcam and many others.

The ideological notion behind this was (and still is on occasion) that there were inherent differences between NPN and PNP devices and that because of them, no true match could ever be made. And obviously that a true match could be made only by using NPN devices alone.

And they were not alone, quite a number of Continental audio companies did more or less the same, including some giants, namely Philips. When Philips produced its best ever series of audio devices (preamp, power amp and tuner) in their US department, their A 22AH578 200 WRMS/8 Ohms power amp used NPN devices only. A very much American topology popular in those days (op amp input, preceeded by an active buffer), however unlike US designs of the day, it used only NPN output devices (355N1, four pairs per channel).
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Old 2nd April 2013, 10:47 AM   #8763
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For many years, while PNP outputs were readily available, they cost far more than their NPN partner
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Old 2nd April 2013, 03:34 PM   #8764
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Yes, there's that, too.
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Old 2nd April 2013, 04:50 PM   #8765
mjona is offline mjona  New Zealand
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Default Linsley-Hood's Book

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Originally Posted by fas42 View Post
Thanks for the pointer ...
I recommend you form your own judgments on the book.

Michael J.
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Old 2nd April 2013, 05:58 PM   #8766
mjona is offline mjona  New Zealand
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Quote:
Originally Posted by PlasticIsGood View Post
Best thing about the book is that it's a story. Especially for a novice, seeing how a circuit works isn't the same as knowing why it's used, which is generally a matter of history.

It's probably a very English history, and partisan in several respects, but illuminating all the same. Not up to date though, obviously.

If I remember his story, life was a struggle for transistor power output stages until reasonably matched NPN, PNP pairs became available. Can't much remember why...problem of symmetrical drive for PP I guess.
That is your opinion from having read the book a long time ago?

Michael J.
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Old 3rd April 2013, 04:27 AM   #8767
mjona is offline mjona  New Zealand
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Quote:
Originally Posted by dvv View Post
Very, very British.

There are quite a few British audio companies which used quasi-complementary output stages way after more than enough complementary devices was available. Naim, Arcam and many others.

The ideological notion behind this was (and still is on occasion) that there were inherent differences between NPN and PNP devices and that because of them, no true match could ever be made. And obviously that a true match could be made only by using NPN devices alone.
Linsley-Hood published an article in Wireless World in June 1970 as a prelude to a Class AB design using complementary transistors.

In this he illustrated the assymetrical waveform of complementary pairs at HF. The article is available online at at http://sound.au.com/tcaas/jlhab1.

The assymetry arises because majority carriers are electrons in NPN transistors and these have greater mobility than the holes which are the equivalent carrier in PNP transistors.

Improved Quasi Complementary stages are worse than Complementary at LF however corrective feedback can be quite effective in that regard.

Corrective feedback is less able effective with problems that arise at HF as with complementary systems.

It is probably easier for the enthusiat to make a complementary system work properly but I would not knock the efforts of Naim, Cyrus and others who have elected to persist with the Q/C layout.

Michael J.
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Old 3rd April 2013, 09:26 AM   #8768
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My memory says that when amps went wrong often the NPN survived . Even now when I push things to the limit the PNP will let go first . I feel that an all NPN output stage is often rejected because on paper it looks to have worse distortion . If this distortion is due to crossover or asymmetry is often overlooked , the asymmetry being less detrimental I feel . The Quad 303 has very low crossover distortion and is a Quasi-comp triple . I wonder if the Quad circuit would be better than many realize , not least with modern transistors ? I like it's primitive protection circuit . I find none work correctly so at least the Quad is easy . A CCS PSU works . It can even have a switch to disable it . For me that should have a wine detector override .

Douglas Self shows a NPN / PNP output stage where the transistors are able to fully discharge the junctions , it is also the simplest he shows . This would be justification enough for NPN/PNP . MOS FET's do not have this problem .
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Old 3rd April 2013, 07:19 PM   #8769
benb is offline benb  United States
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Originally Posted by mjona View Post
The article is available online at at http://sound.au.com/tcaas/jlhab1.
That's an incomplete URL, but I found it here:
The Class-A Amplifier Site - JLH Class-AB Amplifier

Quote:
Originally Posted by nigel pearson View Post
Douglas Self shows a NPN / PNP output stage where the transistors are able to fully discharge the junctions , it is also the simplest he shows .
Perhaps this is discussed in some thread or book I haven't read (I've seen Self's website, but haven't read his nor Cordell's book), but I recall something about this before, that in a push-pull BJT circuit, it's advantageous to totally turn OFF the non-conducting transistor to get lower crossover distortion. Why is this?

"Fully dicharge the junctions" sounds like the BE capacitance creates a problem, but I'm trying to see what that problem is.
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Old 3rd April 2013, 08:35 PM   #8770
mjona is offline mjona  New Zealand
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Quote:
Originally Posted by nigel pearson View Post
My memory says that when amps went wrong often the NPN survived . Even now when I push things to the limit the PNP will let go first . I feel that an all NPN output stage is often rejected because on paper it looks to have worse distortion . If this distortion is due to crossover or asymmetry is often overlooked , the asymmetry being less detrimental I feel . The Quad 303 has very low crossover distortion and is a Quasi-comp triple . I wonder if the Quad circuit would be better than many realize , not least with modern transistors ? I like it's primitive protection circuit . I find none work correctly so at least the Quad is easy . A CCS PSU works . It can even have a switch to disable it . For me that should have a wine detector override .

Douglas Self shows a NPN / PNP output stage where the transistors are able to fully discharge the junctions , it is also the simplest he shows . This would be justification enough for NPN/PNP . MOS FET's do not have this problem .
Apart from my incorrect spelling of asymmetry the link I provided in my last post was corrupt.

It should have read The Class-A Amplifier Site - JLH Class-AB Amplifier. There is a brief mention of the Quad 303 in that reference. The 303 receives a mention in the reference above as well as in Linsley-Hood's book.

In regard to the assertions that quasi comp is very,very British I would like to add that amplifier applications based on Baxandall's version of these output stages made it into RCA Power Devices handbooks possibly as early as 1970.

My edition of the Handbook 1978 includes a complementary output design with cross coupling of the driver emitters. I built a few amplifiers using this idea soon after acquiring the Handbook.

I once had a Quad 33/303 on loan from a friend - it was pretty bullet proof. Sometimes you learn something from restoring such equipment but I had to give this one back.

Michael J
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