[PinkFloyd]

This has been mentioned in the WNA thread and WNA will make up composite opamp adaptor PCB's if there's enough interest shown to warrant a batch being made up.

They are described thus:

In very general terms using two opamps enclosed within a single feeback loop allows you to make a composite opamp with the best features of the constituent opamps. This was popularised by Walt Jung with an AD744 and an AD811 in tandem. You could try an AD843 with an LM6171 for example. My adaptor puts two surface mount opamps on an adaptor, one on top and one on the bottom, so you can plug the composite opamp in place of a single opamp. I designed two pcbs; one with the resistors ( surface mount of course ) that you need on the adaptor pcb, which limits the flexibility somewhat. The other has no resistors on the adaptor and brings a couple of circuit nodes out to pins 1 and 5 which are normally unused by single opamp circuits. In this case you need to solder a couple of resistors on the back of the main pcb in order to use the adaptor, but you can make a much larger range of composite opamp configurations and changing the resistors is much easier. I guess that most people would prefer the second configuration because it involves less mucking about with surface mount parts.

Well, I'm down for a couple of boards with the resistors.

Mike.

 

[rickcr42]

to be honest man that makes no sense to me

The WNA has an opamp then a discrete output stage so at these current levels an Op-Amp/CFB amp compound amp then a discrete output stage seems to me redundant when the CFB stage already has the current levels provided by the discrete stage and adding additional stages can only overcomplicate the simple and have just more variables added without,as far as I can tell,no advantagous attributes unless i am missing something obvious.

either discrete current gain stage or integrated current gain stage but why both unless for a loudspeaker amp and even then there seems to be better methods available

 

[00940]

A classical opamp is first a voltage gain stage (differential pair+VAS) and then a current gain stage (usually push pull).

What Jung is doing is using an AD744 because you can take the signal out of the opamp BEFORE the push-pull output stage of the opamp. He then use an AD811 as a better current buffer than what is included inside the AD744.

It has been discussed earlier. When you have an amp with a discrete output stage, you can just use an AD744, the discrete output stage replacing the AD811 of Jung.

 

[PinkFloyd]

Quote:

Originally Posted by rickcr42 to be honest man that makes no sense to me

A three pin plug seems like rocket science to me ATM Rick so consider me confused also.

IC removed.

Mike.


Edit: "Toothache"

 

[rickcr42]

Quote:

What Jung is doing is using an AD744 because you can take the signal out of the opamp BEFORE the push-pull output stage of the opamp. He then use an AD811 as a better current buffer than what is included inside the AD744.

dude not only do I know what a compound amp is but the what and why of it (operation) so again my question is :

Why use a buffer AND a discrete output stage with an opamp front end ?
Two stages performing one duty is not something that makes sense to me.If the video amp/CFB Amp stage is already providing the current gain needed to drive the headphones why have an additional discrete current gain stage following this ?

no more than one C-Stage is needed to do the job and putting two current gain stages back to back is not neccessary unless the end goal is to have a very high output current (on the order of amps and not milliamps)and the base drive current needs to be high and even then I can think of better ways to get that done.
This would be not headphone amp territory but power amp current output for driving a loudspeaker.

 

[00940]

Quote:

Originally Posted by rickcr42 dude not only do I know what a compound amp is but the what and why of it (operation) so ...

explanation was not for you

 

[rickcr42]

gotcha

 

[nikongod]

i presently have my aph-47 amp setup this way (diferent op-amps drive load as pair), and my diy ballanced amp (one opamp for gain, a totally diferently speced one for "inverted side") the sound is the hotness.

it would be nice to make a "plug-in" adapter to allow you to mix chips on a ppa for example.

can it be as simple as pluging 2 chips into a specially made board? do resistor values need to be changed?

 

[PinkFloyd]

This is an interest check thread....... love them or hate them are you interested in buying a PCB for £3 (or a lot less in a group buy scenario ?

Pinkie.

 

[12796]

I am riding the wagon behind you pinkie! I plan to try them out as well