Discrete Opamp Open Design

diyAudio Member RIP
Joined 2005
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 :D
 
diyAudio Member RIP
Joined 2005
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.
 
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Disabled Account
Joined 2012
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 ... :devilr:

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
 
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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.
 
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.

I am sick of designing discrete opamps in late 70'th when I believed that it is the building block of the future that outperformed everything else, including tubes. I was young and hot then. :D

Ok, let it be not discrete, let it be hybrid. But what the point of using discrete transistors when using a couple of chips and few resistors outperform? ;)
 
I am sick of designing discrete opamps in late 70'th when I believed that it is the building block of the future that outperformed everything else, including tubes. I was young and hot then. :D

Ok, let it be not discrete, let it be hybrid. But what the point of using discrete transistors when using a couple of chips and few resistors outperform? ;)

Then there's no point to this exercise I guess? :confused:

An LME49710 + LME49600 will drive most anything really.
 
Then there's no point to this exercise I guess? :confused:

An LME49710 + LME49600 will drive most anything really.

Exactly! Make from them a classical instrumentational amplifier with gain like 70 dB flat beyond audio frequency band and no need for discrete components. Well, to increase PSRR I would probably add voltage stabilizer for the dual input chip, powering the output chip from higher voltages to get better headroom.
 
I didn't think it was possible, but if you're not counting current sources, this one has 8 transistors and 1 current source. It doesn't meet the output offset requirement. Oh, and this is at 2+ Vrms output. So, distortion is lower at 1 Vrms.
 

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Exactly! Make from them a classical instrumentational amplifier with gain like 70 dB flat beyond audio frequency band and no need for discrete components. Well, to increase PSRR I would probably add voltage stabilizer for the dual input chip, powering the output chip from higher voltages to get better headroom.

Sorry, I am wrong. The point in exercises is building muscle masses and great shape of the body and excellent coordination between body and mind. And in knowing behavior and limits of the topology. Go for it! ;)