Discrete Opamp Open Design

[RNMarsh]

Originally Posted by dirkwright

We need a prize.

Fame and fortune isnt enough?

[RNMarsh]

PS Waveb --- that is NOT discrete circuitry. We mean no IC's. As in -- make an opamp without the IC. Then it would be compared to IC form. A version of the AD627 with individual parts - no IC's.

[bcarso]

I doubt there will be anything remotely approaching a consensus on what this is supposed to be. It's hardly worth the effort. I see the "religious" factions circling already.

But if it spaws umpteen different designs, some of which may actually be built and tested, the efforts might not be all bad.

I'm reminded of the Monty Python Flying Circus sketch about the lethal joke. At one point, after many had died trying to read the joke, teams worked on it in isolation and with individuals being assigned to only one word each. Perhaps this needs to resemble that. The so-called VAS people won't know about the input stage efforts, nor the output buffer. Strictly on a need-to-know basis here

[Kindhornman]

Is this like building a PC or Apple desktop with vacuum tubes........ Can you really outperform a production opamp, and that includes any opamp no cost constraints?

[bcarso]

Originally Posted by Kindhornman

Can you really outperform a production opamp, and that includes any opamp no cost constraints?

Oh certainly [EDIT: at least at audio bandwidths]. "...it happens all the time." But perhaps not with eight active devices. If I were to do this I'd throw out that constraint to begin with. Again (as I remarked in the Blowtorch thread) we need to ask what the advantages are of ICs, and although not discussed there, what kinds of things can we do with discretes when unencumbered with the integration constraints.

The restriction to parts that are still readily available is a bi%ch though.

[fas42]

Originally Posted by RNMarsh

PS Waveb --- that is NOT discrete circuitry. We mean no IC's. As in -- make an opamp without the IC. Then it would be compared to IC form. A version of the AD627 with individual parts - no IC's.

What's wrong with having a competition between 2 camps: a "pure" discrete opamp, vs. a hybrid using ICs, which then sounds "better" ... heh, heh ...

Frank

[RNMarsh]

Originally Posted by fas42

What's wrong with having a competition between 2 camps: a "pure" discrete opamp, vs. a hybrid using ICs, which then sounds "better" ... heh, heh ...

Frank

I'm interested in all but more interested in Scott doing a discrete (with help choosing transistors etc) similar to IC opamp 627, first. Because we need to answere if a discrete sounds the same or better than IC. he does/did opamps and has intimate knowledge of the 627 so who better to try a discrete version?

Lets help him do that. -RNM

[dirkwright]

Originally Posted by RNMarsh

It must be competitive with what is out there already.
It is less of a challenge to do better with more.

[ I could allow cascoding to be considered as a single transistor if it cant be done otherwise. Current sources, diodes might not be counted]

BUT - Scott wanted to do a discrete version for audio of the 627 opamp and that is fine with me. I dont want to start doing something Scott did not say he wanted to do.

A discrete opamp circuit of 627 opamp would be nice for others to compare with the integrated version.


-RNM

So the 627 opamp can drive 30 ohms no problem? I mean, we're talking about a headphone amplifier, not an opamp.

[dirkwright]

Originally Posted by bcarso

...although not discussed there, what kinds of things can we do with discretes when unencumbered with the integration constraints.

I guess higher voltages and currents? At least in the opamp world anyway.

[dimitri]

A version of the AD627 with individual parts

Richard, AD627 is micropower opamp. Do you mean ADA4627, the substitute for OPA627?