Class Ab Oposite Topology

sakis · 28th December 2007, 09:02 AM

i come across this schematic which looks very nice but can somebody tell me this reverse topology like having the matching resistors in the power supply section exactly oposite than normal design ....does it beneffit something ????

design wise or electrically looking at actually its the same thing but when you design amps there should be a difference ..... any opinions ????

phase_accurate · 28th December 2007, 09:30 AM

It is a Sziklay (spelling ??) output stage. It can be designed with voltage-gain >1. And this has actually been done here. One of the practical advantages is the possible usage of driver transistors with lower Vce capability in this case.
A practical disadvantage are possible stability problems (C8 and C9 are there for a reason !!).

A theroretical advantage is to create a nested NFB loop with high loop gain. How much practicla advantage can be taken from this depends on the designer's skills.

Regards

Charles

Donk · 28th December 2007, 10:23 AM

Hi guys,

Sakis, search for ETI-480. That's an Aussie 50/100W amplifier design from the late 70's.
Strange translation, Sakis (bad translation software maybe?). I cannot see any "matching" resistors in any power supply here. You attached the schematic of the ETI-480 amplifier - I cannot see any power supply circuit. Maybe you mentioned "output stage"?
The same about "reverse topology". I can't see any reverse topology here.

PhaseAccurate, you're almost right about spelling. He was called "Sziklai". He born (or he was living there?) in Mid-Europe, Hungary.

sakis · 28th December 2007, 10:32 AM

you like to have a detailed explanation

there you go......

matching resistors are the resistors located normaly in the emmiter of every output transistor in cases of more than two transistor exist to match the digfference between the two transistor .....

normally this setup is located in the output section IE the collector of the transistor is tied to the power supply and the emmiter to the output of the amp .....

this one is the oposite ......

beyond the defination of terms i was looking for some information about the one or the other topology and why .....and this also refers to the output stage not the drive circuit ......

Leolabs · 29th December 2007, 01:46 AM

Something weird with Q8,should connect to the collector of Q5.

28th December 2007, 10:32 AM	#4
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	i presume you like to have a detailed explanation there you go...... matching resistors are the resistors located normaly in the emmiter of every output transistor in cases of more than two transistor exist to match the digfference between the two transistor ..... normally this setup is located in the output section IE the collector of the transistor is tied to the power supply and the emmiter to the output of the amp ..... this one is the oposite ...... beyond the defination of terms i was looking for some information about the one or the other topology and why .....and this also refers to the output stage not the drive circuit ...... __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

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28th December 2007, 09:30 AM	#2
phase_accurate diyAudio Member Join Date: May 2002 Location: Switzerland	It is a Sziklay (spelling ??) output stage. It can be designed with voltage-gain >1. And this has actually been done here. One of the practical advantages is the possible usage of driver transistors with lower Vce capability in this case. A practical disadvantage are possible stability problems (C8 and C9 are there for a reason !!). A theroretical advantage is to create a nested NFB loop with high loop gain. How much practicla advantage can be taken from this depends on the designer's skills. Regards Charles

28th December 2007, 10:23 AM	#3
Donk diyAudio Member Join Date: Sep 2007	Hi guys, Sakis, search for ETI-480. That's an Aussie 50/100W amplifier design from the late 70's. Strange translation, Sakis (bad translation software maybe?). I cannot see any "matching" resistors in any power supply here. You attached the schematic of the ETI-480 amplifier - I cannot see any power supply circuit. Maybe you mentioned "output stage"? The same about "reverse topology". I can't see any reverse topology here. PhaseAccurate, you're almost right about spelling. He was called "Sziklai". He born (or he was living there?) in Mid-Europe, Hungary.

29th December 2007, 01:46 AM	#5
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Something weird with Q8,should connect to the collector of Q5.

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