Headphone amplifier advice
 

Arny Krueger wrote:
"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.


Just as a FYI, this project isn't hifi. In fact, just the opposite. It is to
train students in simplex radio comms protocols. A modicum of noise and a
frequency response such as 300 Hz -3 kHz would be fine and simulate a radio
link even better. In fact, part of the spec is to be able to inject noise
onto the system :-)

With regard to the headphone audio amp issue, I may just do it in discrete
components. A complementary pair of gp transistors and a half dozen
resistors will probably cost about tuppence :-)

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.


Yes, I appreciate that a proper audio amp would do the job better. But I had
a spare amp section on the quad op-amp so I thought I would try to use that
before looking at other options.

Headphone amplifier advice
 

tony sayer wrote:
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?..


Don't know. But if I can't use the spare section on the existing quad op-amp
to drive the headphone then I may as well go for a purpose designed heaphone
amp as suggested by others in here, or add a bipolar complementary pair.

Headphone amplifier advice
 

In article , TonyL
scribeth thus
Arny Krueger wrote:
"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.


Just as a FYI, this project isn't hifi. In fact, just the opposite. It is to
train students in simplex radio comms protocols. A modicum of noise and a
frequency response such as 300 Hz -3 kHz would be fine and simulate a radio
link even better. In fact, part of the spec is to be able to inject noise
onto the system :-)

With regard to the headphone audio amp issue, I may just do it in discrete
components. A complementary pair of gp transistors and a half dozen
resistors will probably cost about tuppence :-)





Ah!, you should have said that..

I'm sure a few contributors could spec you something in the 300-3400 Hz
area;))...
--
Tony Sayer

Headphone amplifier advice
 

"tony sayer" wrote in message
...
In article , TonyL
scribeth thus
Arny Krueger wrote:
"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.


Just as a FYI, this project isn't hifi. In fact, just the opposite. It is
to
train students in simplex radio comms protocols. A modicum of noise and a
frequency response such as 300 Hz -3 kHz would be fine and simulate a
radio
link even better. In fact, part of the spec is to be able to inject noise
onto the system :-)

With regard to the headphone audio amp issue, I may just do it in discrete
components. A complementary pair of gp transistors and a half dozen
resistors will probably cost about tuppence :-)





Ah!, you should have said that..

I'm sure a few contributors could spec you something in the 300-3400 Hz
area;))...
--

A complementary pair of transistors, as suggested, would have a bandwidth
plenty wide enough for video! But the linearity would leave rather a lot to
be desired, more crossover distortion than the LM324 probably. But I wonder
if Tony L has read the data sheet for the LM324?, it clearly states that
with an AC coupled load (I assume he has capacitively coupled his
headphones?) a resistor should be connected from the output pin to ground
"to avoid crossover distortion", has he done that?

David.

Headphone amplifier advice
 

tony sayer wrote:
Ah!, you should have said that..

I'm sure a few contributors could spec you something in the 300-3400
Hz area;))...


LOL !

Headphone amplifier advice
 

David Looser wrote:

A complementary pair of transistors, as suggested, would have a
bandwidth plenty wide enough for video! But the linearity would leave
rather a lot to be desired, more crossover distortion than the LM324
probably.


Not in class AB mode ?

But I wonder if Tony L has read the data sheet for the
LM324?, it clearly states that with an AC coupled load (I assume he
has capacitively coupled his headphones?) a resistor should be
connected from the output pin to ground "to avoid crossover
distortion", has he done that?

Yes, I have the data sheet. With the headphones connected the resistor had
the effect of moving the crossover point up or down from the 0V level
depending on whether the resistor was connected to +Vcc or -Vcc. The value
of the resistor determined how far the crossover point moved. I guess the
idea is to set it so that the output stage goes into Class B mode at higher
signal levels so that the crossover distortion would be buried in the
signal. Unfortunately, it is so bad that it is still clearly audible at all
but very high levels. Moving the crossover point beyond the maximum output
voltage swing removed the distortion but left me with a class A output
stage, with associated high quiescent current. I'm willing to accept that
this problem may be due to trying to drive a low-z load with an
inappropriate device.

Headphone amplifier advice
 

TonyL wrote:

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

Then you're screwed if you need any volume. Most op-amps current limit at around
30mA =~ 20mA RMS. That's 13mW.

Graham

Headphone amplifier advice
 

TonyL wrote:

I built a prototype using a LM324 that happened to be handy. Result was
gross crossover distortion

The LM324 is world reknowed for that. Why not use an AUDIO op-amp ?

Graham

Headphone amplifier advice
 

Arny Krueger wrote:

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

Very true.

Graham