Op amp to Discrete Conversion - Possible?

[apehead]

Would it be possible to convert a preamp using op amps to transistors?

[Enzo]

ANything is possible, but it would be highly impractical. The circuits would be nothing alike, and a whole new circuit board would be required.

[David Schwab]

There are some plans on the internet showing a discreet op amp made from transistors, but I'm sure it doesn't function like the real thing.

The question is why would you want to do this? There's nothing wrong with the sound of a good op amp.

[apehead]

I just mistrust IC's, that's all. I have an ART tube MP that I wanted to hot rod a bit.

[R.G.]

Originally Posted by apehead

I just mistrust IC's, that's all. I have an ART tube MP that I wanted to hot rod a bit.

Sigh.

Would it be possible to convert a preamp using op amps to transistors?

Absolutely yes! It will require a redesign from the sheet metal up, though; it will use more power, have higher - and more objectionable - distortion, and be dramatically more prone to drift, aging and parts tolerances.

And why is it you trust transistors more than IC's?

[apehead]

Because I almost always prefer the sound of an older, discrete circuit to any chip based amps I've heard.

[Steve Conner]

That's probably because of the circuit topology, though, not the components. What do you think op-amps are made of inside?

I disagree with R.G. on the objectionable distortion, though. A discrete JFET preamp with no global feedback will have sweet-sounding distortion that an op-amp (either monolithic or discrete) won't.

[David Schwab]

Originally Posted by apehead

I just mistrust IC's, that's all.

IC op amps are made of transistors... they are pretty much made the exact same way. An op amp is a small multi transistor circuit, all in one package. That's why it's an "integrated circuit."

Originally Posted by apehead

I have an ART tube MP that I wanted to hot rod a bit.

it's not going to be hotrodding it. Swapping IC's for better ones would be though.

[tedmich]

Originally Posted by R.G.

Sigh.


Absolutely yes! It will require a redesign from the sheet metal up, though; it will use more power, have higher - and more objectionable - distortion, and be dramatically more prone to drift, aging and parts tolerances.

And why is it you trust transistors more than IC's?

a light coat of this is reported to cure op amps (and most everything else) of their non-musical character:
http://www.trt-wonder.com/page10.html

he goes on for pages (the spray can is $100) and includes a description of an "infinitely blind" experiment which makes Clever Hans sound like particle physics...

they sell caps too
http://www.trt-wonder.com/page20.html

things did sound better when I was a kid...before all that loud music took its toll on my ears.

[Don Moose]

For all the work you're looking at investing in this, why not think about tube op-amps?

[Enzo]

Hey! The original Philbrick units. Those are a favorite of Bob Pease at National.

[jrfrond]

The generalization that discrete sounds better than opamps is entirely unfounded. I've seen, heard and repaired crappy-sounding discrete designs, and wonderful-sounding opamp designs e.g Music Man.

Sure, you can do a wholesale rebuild on anything, but all you'll be able to use is the chassis and possibly the power transformer, because the circuit board will have to be designed from the ground up.

[Don Moose]

Irregular, but enthusiastic reader of Pease Porridge.

[Enzo]

His troubleshooting analog circuits book is a personal favorite - I learn something new every time I read it.

[gbono]

wow, I can't believe that Bob was laid off by NSC in March - sign of the times. I bet NSC hired outside "consultants" to make that brilliant decision

[tedmich]

Originally Posted by apehead

Would it be possible to convert a preamp using op amps to transistors?

Yes! Check this unit:


its a Burson audio all discrete dual op amp ready to snap into your DIP socket and tower over your circuit board,,,for $147.67 at hificollective

[Enzo]

Does it come in surface mount too?

[imaradiostar]

Originally Posted by Steve Conner

That's probably because of the circuit topology, though, not the components. What do you think op-amps are made of inside?

I disagree with R.G. on the objectionable distortion, though. A discrete JFET preamp with no global feedback will have sweet-sounding distortion that an op-amp (either monolithic or discrete) won't.

I once simulated and designed boards for (but never completed) a neve ba283 module with slight mods so it would replace the mic pre op-amp in my yamaha console. The console already had transformers out front for CMR so all I needed was gain and the Neve circuit would do nicely.

If I had to do it today I'd probably arrive at a J201 or LND150 or similar with a mosfet source follower. I'd use a large cathode bypass cap in line with a trim pot for a "factory set gain trim" and use resistive dividers and negative feedback with multi-pole switches for user gain adjustment a la early neve or trident a-range.

That said- the best thing to do with an ART tube mp is leave it alone. It works so let it be. Build something different and learn from it. Try some of the stuff from Tape Op magazine. check this out: Hamptone JFP DIY

jamie

[Steve Conner]

Originally Posted by tedmich

Yes! Check this unit:
its a Burson audio all discrete dual op amp ready to snap into your DIP socket and tower over your circuit board,,,for $147.67 at hificollective

:O

Do the guys who buy these things ever think about how many op-amps their album went through in the studio? I don't see why they have to hate on our little eight-legged friends. It's a scientific fact that the distortion on something like a NE5532 is inaudible, in fact you can prove it to yourself in a home lab using a null test.

Burson quote THD of 0.0000whatever% for their discrete op-amp, so to me that says their distortion is inaudible too, and you're paying $148 to get no change at all.

Of course the above statements apply at low gains, where negative feedback hides all of the amp's inherent distortion. If you take most of that feedback away, pushing the amp towards the limits of the gain it's capable of, for instance if you're running an op-amp with a gain of 60dB in a mic pre, then it might start to show its character. Since the open-loop gain of an op-amp falls with frequency, it'll show that character in the high end first. If the amp has a Class-AB output stage, it may be an unpleasant character with crossover distortion.

So for something like a mic pre, I'd choose a circuit like Jamie's. A single-ended JFET input to make the distortion sweet, and a Class-A source follower output that can't generate nasty crossover distortion. Some designers like to take ordinary op-amps with Class-AB outputs, and hang a big DC load off the output, which essentially skews them into Class-A.

And remember "All components on the silicone dice are formed by droplet of chemical." So they must sound bad, right?

[dai h.]

Originally Posted by imaradiostar

That said- the best thing to do with an ART tube mp is leave it alone. It works so let it be. Build something different and learn from it. Try some of the stuff from Tape Op magazine. check this out: Hamptone JFP DIY

jamie

seems it'd make more sense to start with something better if you want a good sounding mic pre rather than going off on a esoteric direction with something that doesn't appear particularly great to begin with. My take on those starved plate "tube pre amps" are that at best they provide a bit of colour to the signal but at worst cheap junk hitching a ride to the "warm tubes" bandwagon.