"TonyL" wrote in message


I want to drive low-z (32 ohm) headphones using op amps.

For various reasons I need:

1) Quad amps to be used, there's a requirement for other
op-amps in the units.

That one is probably a non-starter, for reasons I'll detail below.

2) Single rail, around 12-15 V, I guess most modern op
amps will do that easily.

Yes.

3) Not too current hungry, I want to power a number of
these units from one simple 12VDC transformer supply.

The application defines the current drain.

4) Lo-fi will do so long as distortion is not too gross.
Intercom quality is OK.

No need to compromise sound quality.

5) Reasonable cost.

I built a prototype using a LM324 that happened to be
handy. Result was gross crossover distortion when the
output had to supply current to the low-z earphones.

Read the spec sheet and do the math. What sort of voltage will you need to
drive headphones? How much peak current does this net out to be?

I know these amps can be biased into class A operation but
I want reasonable power economy. Would be nice to just
drop a pin compatible device into my prototype, say a LM
387 ? Except the spec says
600ohms load.

Advice/comments please ?

Quit pulling numbers out of your memory from days long ago, and do what
professional engineers do when they have a task like this: Go to several op
amp manufacturer sites like TI, National, Maxim, NJM and Philips, and see
what they recommend for the purpose.

There are even such things as op amps that are designed to drive low
impedance loads and work from single-ended supplies.

The odds that they will be quads is about zero, since headphone drivers are
typically used in pairs.