Collection of Class B topologies <100mA Idle and Sound closest by Class A - diyAudio
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Old 3rd March 2010, 02:40 PM   #1
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Default Collection of Class B topologies <100mA Idle and Sound closest by Class A

Until now, it is still a challenge, to create a solid state power amplifier with <100 mA quiescence current through the power output devices and sound quality like pure class A at the same time.
Unfortunately I haven't heard such an amplifier until this day.
The same observation has also made Mr. Nelson Pass - go to
http://www.passlabs.com/pdf/articles/seclassa.pdf (third paragraph) and
http://www.passdiy.com/pdf/leaving_class_a.pdf

But below a collection of topologies, that most likely could reach the very clean sound of class-A without any harshness.
There are probably more of such circuit topologies and I want to know others (except Class D).
What about your audible experiences - what you would say, which topology is closest to Class A regarded the sound?
Thank you very much for your comments.

1) P.J. Walker Current Dumping Audio Amplifier"
http://220.232.128.43/audio/quad405/...J%20Walker.pdf
Quad 405 DCD mod3 - PCB
2) N.M.Visch "A Novell Class B output"
Class B w/o crossover distortion (1975)
3) Yamaha's Hyperbolic Conversion Amplification (HCA) Circuit
Yamaha's Hyperbolic Conversion Amplification (HCA) Circuit
4) NDFL = Nested Differentiating Feedback Loops
New Cherry NDFL amp
http://www.diyaudio.com/forums/solid...s-some-example
5) ERCO from diyaudio member "turnA_zpoint "
http://www2.plala.or.jp/puthoff/MJ.html
http://www2.plala.or.jp/puthoff/mate...ork_081030.pdf
http://www2.plala.or.jp/puthoff/material/EXP_MK2_V2.pdf
MJ Magazine (formerly Musen to Jikken) - Yearly Index from 1924 - 2009 wanted (Post # 11)

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Old 3rd March 2010, 04:20 PM   #2
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Here the next circuit I have found: JBL's bridged T-circuit
http://www.harman.com/EN-US/OurCompa...tions/1091.pdf
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Old 3rd March 2010, 07:11 PM   #3
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Current-dumping (feed-forward) applied to a conventional Class-B amplifier topology (a number of variants are possible):

Current-dumping Class-AB Self Type-II EF O/P

The darlington O/P version won't qualify as Class-A sonics, but variants that use a Class-AB Self Type-II EF output stage along with current-dumping get close to Class-A sonics.

Also, it is possible to combine current-dumping (feed-forward) with the Visch Class-B topology, which should yield sonics which are comparable to high-end Class-A.
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Old 1st July 2010, 07:19 PM   #4
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Quote:
Originally Posted by linuxguru View Post
Current-dumping (feed-forward) applied to a conventional Class-B amplifier topology (a number of variants are possible):

Current-dumping Class-AB Self Type-II EF O/P

The darlington O/P version won't qualify as Class-A sonics, but variants that use a Class-AB Self Type-II EF output stage along with current-dumping get close to Class-A sonics.

Also, it is possible to combine current-dumping (feed-forward) with the Visch Class-B topology, which should yield sonics which are comparable to high-end Class-A.
very interesting. Do you know commercial models uses this Vish Class-B topology?

Here various URLs with topologies, which all have one goal:
to outwit the disadvantages of Class B:

New Class A, Super-A, Non-Switching : need a revival ?
Bootstrapped ClassA - ?
New-Class-A ? (whats it mean)
Technics Class A Bias Circuits
Technics Class A Biasing
New Class A, Super-A, Non-Switching : need a revival ?
Technics Class-AA / Sandman Bridge
Class AA Opamp Schematic
Now AA is down?
Classes of operation vs. sound quality
Pass Patent 5,343,166

For me follow topologies seems to be closest to pure class-A (have a look also to the attached PDF):
:: Audiotek 69 - [Technics SE-A1?] ::
Power amplifier

Here some papers about THD measuring procedures and effects by Class-B:
ELECTRONICS & WIRELESS WORLD JULY1987 1.95
Crossover distortion in class-B amplifiers
Detailed tests on three modes of amplifier operation, including
a non-switching class Btype, using the same basic circuit
produce a fewsurprises. E. MARGAN :
http://www-f9.ijs.si/~margan/Articles/Class_B_Dist.pdf

LM4702 driving the MOSFET output power buffer
http://www.national.com/an/AN/AN-1645.pdf
Attached Files
File Type: pdf Elektor class-B drives class A supply.pdf (100.6 KB, 325 views)
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Old 22nd March 2011, 11:08 AM   #5
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Are there any new commercial products (except Class-D) that match the sound character of class a (at least nearly) ??
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Old 22nd March 2011, 01:35 PM   #6
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by tiefbassuebertr View Post
Until now, it is still a challenge, to create a solid state power amplifier with <100 mA quiescence current through the power output devices and sound quality like pure class A at the same time.
Unfortunately I haven't heard such an amplifier until this day.
How about this one, it could qualify as it has an Iq=50mA:
UniGaBuf, a follower cut out to be a leader.
I have another contender, a sliding class A circuit, but the Iq is ~180mA.
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Old 22nd March 2011, 02:25 PM   #7
KanedaK is offline KanedaK  Belgium
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Quote:
Originally Posted by tiefbassuebertr View Post
very interesting. Do you know commercial models uses this Vish Class-B topology?

Here various URLs with topologies, which all have one goal:
to outwit the disadvantages of Class B:

New Class A, Super-A, Non-Switching : need a revival ?
Bootstrapped ClassA - ?
New-Class-A ? (whats it mean)
Technics Class A Bias Circuits
Technics Class A Biasing
New Class A, Super-A, Non-Switching : need a revival ?
Technics Class-AA / Sandman Bridge
Class AA Opamp Schematic
Now AA is down?
Classes of operation vs. sound quality
Pass Patent 5,343,166

For me follow topologies seems to be closest to pure class-A (have a look also to the attached PDF):
:: Audiotek 69 - [Technics SE-A1?] ::
Power amplifier

Here some papers about THD measuring procedures and effects by Class-B:
ELECTRONICS & WIRELESS WORLD JULY1987 1.95
Crossover distortion in class-B amplifiers
Detailed tests on three modes of amplifier operation, including
a non-switching class Btype, using the same basic circuit
produce a fewsurprises. E. MARGAN :
http://www-f9.ijs.si/~margan/Articles/Class_B_Dist.pdf

LM4702 driving the MOSFET output power buffer
http://www.national.com/an/AN/AN-1645.pdf
I own (and use daily in my main system) a Technics SE-A5 wich uses the "New class A SynchroBias" circuit. I use it with horn speakers, 104dB, and I can confirm this is an amp that sounds clean and full even at very very low power (0,01watt in most of my evening listenings). Is it a result of the New class A circuit or other factors I cannot tell, but it sure sounds good. A lot of big SS amp i've tried so far were quite "grainy" and "dirty" when driving the same speakers.
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Old 23rd March 2011, 01:09 AM   #8
ontoaba is offline ontoaba  Indonesia
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Quote:
Originally Posted by tiefbassuebertr View Post
Are there any new commercial products (except Class-D) that match the sound character of class a (at least nearly) ??
You mean sound character is beautiful 6kHz? and up?
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Old 23rd March 2011, 04:13 PM   #9
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Quote:
Originally Posted by ontoaba View Post
You mean sound character is beautiful 6kHz? and up?
Exactly.
Quote:
Originally Posted by KanedaK View Post
I own (and use daily in my main system) a Technics SE-A5 wich uses the "New class A SynchroBias" circuit. I use it with horn speakers, 104dB, and I can confirm this is an amp that sounds clean and full even at very very low power (0,01watt in most of my evening listenings). Is it a result of the New class A circuit or other factors I cannot tell, but it sure sounds good. A lot of big SS amp i've tried so far were quite "grainy" and "dirty" when driving the same speakers.
Thank you for this informations. I will check this, if I have a possibility.
Quote:
Originally Posted by Elvee View Post
This unity-gain follower is an audiological UFO:
It is adjustment-free, requires no thermal compensation, has no feeedback, no servo, can even work with fake or reject transistors, and yet offers low DC offset and sub-ppm linearity:
Thank you for this circuit - I will check the circuit in my CAD programm, If I have time.

Last edited by tiefbassuebertr; 23rd March 2011 at 04:16 PM.
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Old 24th March 2011, 01:11 AM   #10
ontoaba is offline ontoaba  Indonesia
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ClassAB with bootstrap will have 10kHz sounds better than 6kHz. In high quality classA, 6kHz beautifully beat 10kHz and everything sounds beauty and real. I found it when play with damper characteristics.
ClassA drop characteristics has major cause. When classA using huge feedback to achieve lowest distortion, that drop characteristics is gone, and it sounds like common amplifier.

I post some picture here, may help too.
Alternative topologies
post#30
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