Butte Headpone amp PSU

[lars-musik]

I recently finished a headphone amp (the Millett "The Butte") to drive my Sennheiser HD650s (250 Ohm). I used a symetrical 15V PSU I salvaged from some discarded machine from work long ago and it works fine. However, the whole affair is LARGE and me, an old 1590a devotee, would like to shrink it. Plus I'd like to power the thing with a standard DC-adaptor (the original utilizes an AC supply).

So now here's my question:
I can't for the life of me figure out, what the current demand of this circuit is when driving headphones (atm I use 250 Ohm phones but it should be able to drive up to 600 Ohm).

This is the original cicruit:




And here's what I'd like to do (LT1054 powered)



The LT1054 supplies 100mA max. The opamps are those:

http://www.ti.com/lit/ds/symlink/opa551.pdf

Do you think it could work?

Cheers, Lars

Larger Images:

[PRR]

Depends a LOT on what those MOSFETs are biased at.

For +/-12V supply the opamp needs 9mA static. With 250 Ohm load driven to clipping you need 15mA dynamic supply current. But I figure the FET is biased near 23mA, which swamps the dynamic current (it runs class A). So it is 32mA per channel.

Note that this is 200mW in 250 Ohm load which is WAY too loud for the HD650!! But does not change much with signal so that's what you need. (You could surely be happy with +/-9V, even +/-6V if budget is tight.)

Even at 600 Ohms it makes 80mW which ought to be ample for anybody.

Pete's design will happily drive 32 Ohm loads to 1,500mW, which is insane. And on test-bench, dynamic supply current will be 120mA per channel. Again, I would aim for lower supply rails.

[lars-musik]

PRR! Great as always. All the info I need and then some.
So thanks a lot and all the best,

Lars

[lars-musik]

A small additional question: The opamp used in the circuit is a bit hard to come by. The OPA551 is sold by Reichelt (where I usuallly order), but I had to order the OPA552 at Mouser with overseas shipping.

Do you know either of a (possibly cheaper) substitute? What makes this one special for this circuit?

And/or the differences between 551 and 552 that serious?
The most important ones seem to be the slew rate (15V/µs vs 24 V/µs) and the bandwidth (3 MHz vs 12 MHz). I cannot image that bandwidth to have an impact on the quality of a headphone amp. What about the slew rate?

Here's the complete datasheet for both:
http://www.ti.com/lit/ds/symlink/opa551.pdf

Thanks again!

[PRR]

The '551 will be fine.