Class-A Opamps

[BC]

BUF 03

By the way, if anyone is reading this, here is the "obsolete" data sheet on BUF 03. If you search the internet there are some available. Plan on around 15USD each.


http://home.wi.rr.com/gtgelectronics/BUF03.pdf[/URL]


Bruce

 

[clem_o]

Re: BUF 03

By the way, if anyone is reading this, here is the "obsolete" data sheet on BUF 03. If you search the internet there are some available. Plan on around 15USD each.

Sure there are people reading 'this' - many thanks for the link!

Cheers

 

[sdman]

Class A Amps

I think Bob Carver used this technique in his amps.
Check out Carver and Sunfire amps on Google.

sdman

 

[mlloyd1]

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

Kanwar,

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

 

[BC]

Buf 03

Quick update on the BUF 03. Good news: I found one of the sources for the IC. Bad news: the cost .... 37 USD



http://www.americanmicrosemi.com/products/search/index.php

Just type in BUF03 (no spaces) for part search.

Bruce

 

[thanh]

I intend to build a symmetrical op-amp with class A . But dual-tst is too expensive

 

[amplifierguru]

Yes mlloyd,

That's it SE/NE540L I think for high voltage. Had a variety of operational modes wiwo output devices, from vague recall.

Cheers,
Greg

 

[lineup]

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

 

[amplifierguru]

Hi lineup,

There are many modern op amps that operate enough standing output stage current that they will operate Class A into av high Z load - so they can be lightly loaded with a discrete buffer stage.

Class A may be a goal in itself in low power and preamps but in power amps it's generally a wasteful fallback position.

Cheers,
Greg

 

[lineup]

Okay,

but personally
if I will build a Class A discrete buffer, to help an OP-amp,
I may as well build a good matching input differential pair
while I am at it.
And skip the near to Class B operational amp.

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

 

[amplifierguru]

Hi lineup,

It's nice to put some Re's in there for current sharing and degeneration. Helps to wideband the opamp and increase slew rate as less Ccomp is needed. And keep input stage source (and FB) impedances low.

Cheers,
Greg

 

[peranders]

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 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

 

[lineup]

This is a

TRUE Class A operational amplifier

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

 

[nuvistor]

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.

 

[lineup]

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?

 

[lineup]

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.

 

[peranders]

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

The purpose is to increase the open-loop gain at high frequences, my guess.

 

[TonyTecson]

Those caps are a mystery.

leach calls it lead compensation, as opposed to lag compensation(miller) he used it in the super leach when it first came out in the AUDIO magazine in 1980. then it was dropped in the later versions.

 

[RAYSIMMONS]

se/ne 540 and 541

Signetics Corp ne540 and 541 chips can be used to make very good sounding audio amplifiers

 

[EWorkshop1708]

Re: Re: Class-A Opamps

The simple answer is: If the "industry" wants class A opamps they would be designed and manufactured 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

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.