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Old 1st March 2010, 01:50 AM   #1
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Default How to identify a quasi-complementary amplifier?

How to identify a quasi-complementary amplifier? is it it contains 4 transistors 2 in 1 pair. And each pair is in complement? Does anyone can share some info about quasi-complementary amplifier?

thank you.
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Old 1st March 2010, 02:08 AM   #2
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All output devices are the same type and number.

Either all npn, or all pnp.
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Old 1st March 2010, 02:15 AM   #3
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I believe its common to find all NPN as outputs due to PNP's being difficult to make in the early to mid 70s.
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Old 1st March 2010, 10:06 AM   #4
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Default How to identify a quasi-complementary amplifier?

This is a good question.

Quote:
Originally Posted by AKSA View Post
All output devices are the same type and number.
Either all npn, or all pnp.
Really? Then I must even call the CSPP (Circlotron) and the topologies from Ollson (Better Audio from non complements? from Bengt Olsson, Electronics World + Wireless World, December 1994 page 988) quasi complementary?

I don't think so. I call only such output stages as "Quasi complementary", if it looks like PP true complementary buffer except the lower last power transistor. This means for me, that the upper halve of PP buffer looks like a darlington and the lower looks like a sziklai (CFP) darlington

An complete overview of topologies, where are only NPN-BjT's and N-CH MOSFET's in the last part of power buffer you will find here:
Only N-Channel MOSFETs (NMOS); better Audio from non complements by Audio Power?

also of interest in this case are some articles from the diyaudio member "X-PRO", e. g.
Quasi or not Quasi - that is the question

Last edited by tiefbassuebertr; 1st March 2010 at 10:10 AM.
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Old 1st March 2010, 12:11 PM   #5
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Quote:
Originally Posted by motbuddy View Post
How to identify a quasi-complementary amplifier? is it it contains 4 transistors 2 in 1 pair. And each pair is in complement? Does anyone can share some info about quasi-complementary amplifier?

thank you.
Quasi means acts as if.
So quasi complimentary means the NPN's act as if they were complimentary.

In reality that isnt quite true as one side has more gain than the other due to one side requiring an inverting driver which has gain, where as the other side is a simple driver buffer.

I found the inverting side required a capacitor from collector to base on teh driver transistor to stop oscilation.
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Old 1st March 2010, 01:07 PM   #6
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Quote:
Originally Posted by nigelwright7557 View Post
In reality that isnt quite true as one side has more gain than the other due to one side requiring an inverting driver which has gain, where as the other side is a simple driver buffer.
Yes, and therefore some manufacturers like Quad (model 303, not to interch. to the current dumping version 405) creates three stage super ß devices to avoid (or reduce at least) this disadvantage (see attachement).
But the disadvantage there is the risc of oscillation of the buffer stages itself (not so by use of two stage, darlington for upper and sziklai darlington for lower buffer part.
Only truly experienced (and unfortunately very few) developers (like Quad) achieve a design without any oscillation under any load condition. By many others there are oscillation and hum/buzzing effects through the sensitivity of parasitic influences. If I get such amp devices I must remove one stage in any cases, i. e. the reduce to a two stage PP buffer

By the way, after right service and maintenance the Quad 303 is a very fine sounded amplifier, (much more better than the current dumping version Quad 405 and most true complementary versions). Only power stage versions with much more idle current trough the output can outperform the Quad 303

http://www.net-audio.co.uk/quad303upgrade.html
Quad 33 and Quad 303
Quad 303 : Upgrade output stage to be fully complementary
Quad 303 triple cascade
Attached Images
File Type: jpg quad303 power PP super ß buffer.jpg (28.9 KB, 1126 views)
File Type: jpg quad303m.jpg (98.3 KB, 1111 views)
File Type: jpg Quad 303 inside.jpg (212.9 KB, 1095 views)

Last edited by tiefbassuebertr; 1st March 2010 at 01:27 PM.
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Old 1st March 2010, 02:05 PM   #7
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here basic articles:
Attached Files
File Type: zip Bax.zip (66.3 KB, 179 views)
File Type: zip Lin.zip (63.3 KB, 108 views)
File Type: zip QuadTriple.zip (28.5 KB, 118 views)
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Old 4th March 2010, 03:22 AM   #8
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Does this claim about quasi-complementary correct?

Quote:
Designers also sometimes use a "quasi-complementary" configuration, which uses a Darlington push pair (i.e., two NPN transistors) and a Sziklai pull pair (i.e., one PNP and one NPN transistor). This configuration, which uses three NPN transistors and one PNP transistor, is advantageous because:
  • Silicon PNP transistors have historically been more expensive than their NPN counterparts.[citation needed]
  • The performance of the lower pull pair, which uses a single NPN transistor, more closely matches the performance of the upper push pair, which consists of two NPN transistors.[citation needed]
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Old 24th April 2011, 11:59 AM   #9
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Quote:
Originally Posted by motbuddy View Post
Does this claim about quasi-complementary correct?
Who can perform an exactly investigation of both?
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Old 12th August 2016, 04:32 PM   #10
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Default And how to build a good, simple one

Hi,

quasi-complementary output stages are fine, if done right.

Quote:
Originally Posted by nigelwright7557 View Post
Quasi means acts as if.
So quasi complimentary means the NPN's act as if they were complimentary.
Quasi is Italian for nearly. For me, both swings matched well at all levels and frequencies like this:

* PNP driver transistor uses emitter and collector resistors of equal and same value as NPN driver shunt resistor, hence inverting stage has same small-signal gain as non-inverting stage, for you know unity gain. In a 25 W design this was 220 Ohms.

* A diode is layed in parallel and conducting polarity to PNP emitter resistor. I guess this was 1N4001. This matches great-signal behaviour.

* A capacitor is also layed in parallel at this place. I vaguely remember, this was a few Nanofarads. Value was found by looking at square wave responses.

This turned out non-resonating yet fast enuf, so even using old transistor types, performance turned out fine after setting of a few dozend Milliampères bias, output HF decoupling and non-ringing global feedback.

Unfortunately for a small-multi-channel-system builder like me, discrete Darlington output stages need at least three mounting holes per channel, two for the power transistors and one bracketing both drivers. Is there an integrated chip for this with seven pins, needing only the compensation capacitor and two power shunt resistors for a complete output stage, or even with built-in thermal feedback? Or a truely complementary Darlington pair chip? Or a chip amplifier of this design with most basic voltage amplification stage (single transistor input stage, single transistor second amplification stage with external, bootstrapped collector resistors) for a single supply up to 60V? With small-signal radio, ICs of this "integrate only what profits from integration" philosophy were common, but rare with audio.

Uli
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