Headphone amplifier advice
 

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.
2) Single rail, around 12-15 V, I guess most modern op amps will do that
easily.
3) Not too current hungry, I want to power a number of these units from one
simple 12VDC transformer supply.
4) Lo-fi will do so long as distortion is not too gross. Intercom quality is
OK.
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. 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 ?

Headphone amplifier advice
 

"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.

Headphone amplifier advice
 

"Arny Krueger" wrote in message
...
"TonyL" wrote in message


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

snip

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

Indeed there are. Since 32ohm is now the standard for headphones there are
plenty of heaphone amps intended to drive 32 ohm h/phones on the market.
Mostly they are designed to work from single-ended supplies of around 3-12V

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

Agreed. I know of no quad op-amps that will do the job. I think Tony should
accept that he will need a separate h/phone amp chip.

David.

Headphone amplifier advice
 

"TonyL"

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.
2) Single rail, around 12-15 V, I guess most modern op amps will do that
easily.
3) Not too current hungry, I want to power a number of these units from
one simple 12VDC transformer supply.
4) Lo-fi will do so long as distortion is not too gross. Intercom quality
is OK.
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. 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 ?


** Huh ??

The LM387 is a long obsolete, dual low noise pre-amp.

How about you try a TL074 - exact same pin out as the LM324 and no x-over
issues.

Will deliver about 20mA ( = 13mW peak ) into a 32ohm ear phone, which is
plenty loud.




...... Phil

Headphone amplifier advice
 

David Looser wrote:

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

Agreed. I know of no quad op-amps that will do the job. I think Tony
should accept that he will need a separate h/phone amp chip.

All comments noted. Thanks.

The *only* problem with the LM324 in this application is the crossover
distortion. It drives low-z headphones fine. So, I'll try plugging in a
TL074 and see what happens before looking to a purpose designed hadphone
driver.

Headphone amplifier advice
 

Phil Allison wrote:

How about you try a TL074 - exact same pin out as the LM324 and no
x-over issues.

Will deliver about 20mA ( = 13mW peak ) into a 32ohm ear phone, which
is plenty loud.


I'll give it a try. Thanks.

Headphone amplifier advice
 

In article , TonyL
scribeth thus
David Looser wrote:

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

Agreed. I know of no quad op-amps that will do the job. I think Tony
should accept that he will need a separate h/phone amp chip.

All comments noted. Thanks.

The *only* problem with the LM324 in this application is the crossover
distortion. It drives low-z headphones fine. So, I'll try plugging in a
TL074 and see what happens before looking to a purpose designed hadphone
driver.



Would one of those SSM -whatever -there -called series line drivers do
this quite well?..
--
Tony Sayer

Headphone amplifier advice
 

A mistake that many people make with lo-Z headphones is to run an amp
straight into them and then wonder why there is so much residual noise.

The easiest method is to use a small power amp such as a LM386 or
TDA2003, then put a resistor in series with it - something in the range
330-470R will usually suit. You will probably end up with a far more
acceptable result as the amp is specifically designed to drive audio
rather than just a general purpose amp.



--
Woody

harrogate three at ntlworld dot com

Headphone amplifier advice
 

Woody wrote:
A mistake that many people make with lo-Z headphones is to run an amp
straight into them and then wonder why there is so much residual noise.

The easiest method is to use a small power amp such as a LM386 or
TDA2003, then put a resistor in series with it - something in the range
330-470R will usually suit. You will probably end up with a far more
acceptable result as the amp is specifically designed to drive audio
rather than just a general purpose amp.

That's an impressive damping factor.
I wonder how the frequency response of headphones changes when
current-driven
rather than voltage-driven.

--
Eiron.

Headphone amplifier advice
 

"Eiron" wrote in message


That's an impressive damping factor.
I wonder how the frequency response of headphones changes
when current-driven rather than voltage-driven.

The impedance curves of headphones are documented on the web, and are
typically pretty non-uniform.

Probably why so many people like dedicated headphone amps, and drive them
from low impedance, low voltage sources.