Simple Class-A Chipamp

Moon_Walker · 18th January 2010, 01:45 PM

Hi,

i am just finished my Chipamp project and one of mycolleague in this hobby introduced his design, which i build also last week.

There is no caps in signal path!

I am interesting about your opinion about this concept.
This kind of design should deliver Class-A quality depending on OPA?

Br
Attila

analog_sa · 18th January 2010, 02:58 PM

Do you think TL082 works in class A?

Moon_Walker · 18th January 2010, 07:00 PM

Quote:

Originally Posted by analog_sa

Do you think TL082 works in class A?

Of course not. The buffer transistor works in class-a due to bottom current generator transistor.

analog_sa · 18th January 2010, 07:22 PM

Therefore it is a simple chipamp, but not class A. Unless you bias the opamp in class A as well.

wahab · 18th January 2010, 07:24 PM

an opamp is biaised in class a, providing the
output current pumped by the load is significantly
less than the current consumed by the opamp..

analog_sa · 18th January 2010, 07:30 PM

Sadly i don't know the quiescent current of TL082, nor the beta of the transistors. That's why i asked.

woody · 18th January 2010, 07:37 PM

That 4.7k resistor is not a good way to bias the output transistor curent source.

wahab · 18th January 2010, 07:41 PM

1.4 mA...that s not a lot, and considering that part
of this current is used for internal biaisings, it does left
no more than a few hundreds uA to feed the transistors bases
and still retain class A in the aop output stage..
if you have no need of very high input impedance, you can use
a NE5532 which have a quiescent current of 8 mA, and thus, should be capable of
roviding a few mA in class A mode...

Juergen Knoop · 18th January 2010, 08:51 PM

the opamps output-stage runs always in 'class' A, regardless of its quiescent current etc. Its upper transistor never shuts of because it must always supply a positive current to the discrete stage.
regards

wahab · 18th January 2010, 08:57 PM

Quote:

Originally Posted by Juergen Knoop

the opamps output-stage runs always in 'class' A, regardless of its quiescent current etc. Its upper transistor never shuts of because it must always supply a positive current to the discrete stage.
regards

not at all..
NE5532 is given at 8 mA quiescent current, yet can provide
almost 40 mA to the load...
you can be sure that at more than 8 mA output current,
the output stage is in class B mode..

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18th January 2010, 02:58 PM	#2
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	Do you think TL082 works in class A?

18th January 2010, 07:22 PM	#4
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	Therefore it is a simple chipamp, but not class A. Unless you bias the opamp in class A as well.

18th January 2010, 07:24 PM	#5
wahab diyAudio Member Join Date: Nov 2009 Location: algeria/france	an opamp is biaised in class a, providing the output current pumped by the load is significantly less than the current consumed by the opamp..

18th January 2010, 07:30 PM	#6
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	Sadly i don't know the quiescent current of TL082, nor the beta of the transistors. That's why i asked.

18th January 2010, 07:37 PM	#7
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	That 4.7k resistor is not a good way to bias the output transistor curent source.

18th January 2010, 07:41 PM	#8
wahab diyAudio Member Join Date: Nov 2009 Location: algeria/france	1.4 mA...that s not a lot, and considering that part of this current is used for internal biaisings, it does left no more than a few hundreds uA to feed the transistors bases and still retain class A in the aop output stage.. if you have no need of very high input impedance, you can use a NE5532 which have a quiescent current of 8 mA, and thus, should be capable of roviding a few mA in class A mode...

18th January 2010, 08:51 PM	#9
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	the opamps output-stage runs always in 'class' A, regardless of its quiescent current etc. Its upper transistor never shuts of because it must always supply a positive current to the discrete stage. regards

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