Class-A Opamps

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ampguru:

was that the SE/NE540?

i think it had two outputs for drving complementary output devices, maybe some current limit programming.

very fuzzy memory.

but it was an op amp like gain stage, not a buffer

mlloyd1

amplifierguru said:
Kanwar,

There was a Class A Opamp produced in the 80's although I can't recall whose it was, maybe Signetics or AD...
 
Workhorse said:
Hi everyone,

Has anybody came across Class-A opamps?.
Do they really exist.
Does there is a way in which a regular class-AB opamp could be converted to Class-A opamp.

waiting for replies.......
Regards,
Kanwar🙂 😉


Generally, why is almost no Chip OP-amplifier in Class A
I think is
when you go for an IC ( and not discrete ) Operational amplifier
- you want it simple
- you want it as low power supply as possible
- you might want to build a great number of identical devices


If you want to find TRUE Class A OP-amps, you have to go for discrete.
Like this one by Graham Maynard:


An externally hosted image should be here but it was not working when we last tested it.


Hi-Fi Preamplifier by Graham Maynard
 
Workhorse said:
Has anybody came across Class-A opamps?.
Do they really exist.
The simple answer is: If the "industry" wants class A opamps they would be designed and manufactured :nod: The truth is that the industry is rather satisfied with the present types.

Kanwar, have you thought of that pretty many opamps really do run in class A for not too heavy loads.

Two good class B examples are LM358 and LM324 :bigeyes:
 
This is a

TRUE Class A operational amplifier

It is designed and commercially used
by
Bryston Limited, located in Canada
 

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lineup said:
This is a

TRUE Class A operational amplifier

It is designed and commercially used
by
Bryston Limited, located in Canada

Similar to the line stage of a Hafler DH101/110, except Hafler doesn't include the complimentary EF output stage which really improves output drive. BTW the EF is class AB.

I wonder, what is the purpose of the 47p capacitors? the time constant with the 150R is 7ns.
 
nuvistor said:
I wonder, what is the purpose of the 47p capacitors? the time constant with the 150R is 7ns.

Those caps.
I have not seen this before in an amplifier, not that I recall.
Higher value caps, yes. But not so small.
Must be some compensation.

Reduce noise in those resistors used?
 
nuvistor said:
I wonder, what is the purpose of the 47p capacitors?

Those caps are a mystery.
But here I found another high quality discrete OP-Amp
using same small value cap, in addition to another high freq filter.
I am sure it is some compensation.
Compensation caps are generally in size of pF.
 

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Re: Re: Class-A Opamps

peranders said:

The simple answer is: If the "industry" wants class A opamps they would be designed and manufactured :nod: The truth is that the industry is rather satisfied with the present types.

Kanwar, have you thought of that pretty many opamps really do run in class A for not too heavy loads.

Two good class B examples are LM358 and LM324 :bigeyes:

Too bad I found your post AFTER I built a small preamp using a 324 😱

But thank your for that valuable information.

I will be adding 10k ohm resistors now to all four amps on my chip.

*I thought I was hearing crossover distortion, and I biased my big amp to 300mA (the one the 324 was driving) thinking it was the problem and got no difference, so backed it back down. After doing a test listening to the amp without the 324, the distortion is gone.

I'll be changing the chip soon.
 
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