What Makes An Audio Op Amp An Audio Op Amp?

Define "low".

Nope. FETs work as the amplifier, too.

That too. ;-)

Resistors?

John

The Iq of the opamp keeps both optos on a little all the time, so it's class AB, mild crossover distortion. But sure, it needs feedback to be linear. The opamp is an integrator, so DC error is nill.

This is good for biasing physics-type things, like electrodes in vacuum and such. I first used it to set the voltages in a microchannel-plate delay-line imager for a weird instrument.

If the domiant compensation pole is a biggish cap to ground from the output, that hardens it against arcs and such and obviously makes it capacitive-load tolerant. It's easy to make it short-circuit protected, too.

Think kilohertz, not megahertz.

Another circuit I like is

ftp://jjlarkin.lmi.net/Opto_Totem.JPG

which is a pair of optoisolators working totem-pole. It behaves like cmos, in that there's zero static power consumption on the isolated side.

Optoisolators are great as long as you don't use them the way they were intended.

John

Mosfets have decently high current gain.

John

Herold

Large-but-finite. Gotcha. ;)

(Of course one can't always be sure of the sign.)

Cheers

Phil Hobbs

Kinda defeats the purpose of the isolators.

Herold

Beat me to it. ;-)

The isolators aren't there to be isolators. They are high-voltage gain stages. Can you think of a simpler or cheaper way to get 400 volts p-p swing?

John

That was strangely civil of you!

Many years back ('78 or so) I was using opamp followers mixing multiple frequency sawtooth (max freq 8.1KHz) in a heavily modified Schober electronic organ. I was getting the strangest mixes I could imagine and for an experiment swapped out all the LM324s with TL074s and the problem vanished. My best explanation was output slew rate limits caused some sort of back conduction through the input diff pairs. Plausible ?

G=B2

-50 > and +350, or +2000 and +2400. >

Direct coupled electrostatic headphone amplifier?

G=B2

For "hi-fi" check out the data sheets for

TL072A "just good enough, and cheap" (Similar to LF351 & LF356 ?)

OPA2134 "a bit better"

Besides adequately low noise and high drive, "audio" op amps usually have crap input offsets.

Cheers

Phil Hobbs

Like it matters with audio and DC-centering loops ?:-) ...Jim Thompson

Of course. It saves a few pennies, and nobody cares, so why not?

Cheers

Phil Hobbs

I doubt that it saves pennies, just substantially safer to compensate the loop if you don't overdo the open loop gain. ...Jim Thompson

Has anyone actually used tubes and optoisolators in the same design ?

You worry too much! :)

Just apply a couple of small bypass caps at the OP-AMP rails. That will should give you a little shoot through while it's switching over..

P.S. I noticed that the output there is not going to be symmetrical, but who cares about .7 volts verses .2 when you're dealing 200 volts.

Jamie