headphone powering

[michael_krell]

I am creating a circuit that needs to poewr head phones. so basically a headphone amplifier. I know it needs to be something special to power headphones because they are coils. I measured the impedance of my AKG headphones and they are 120 ohm each. let me know what you guys think i should use. I thought i needed a current amplifier but im not sure

[Mike Burgundy]

You don't need anything special just cause theyre coils, but you do need to supply current, since it's a low-impedance load.
Any amp capable of delivering enough power (milliWatts, nothing too shocking) and capable of supplying enough current should do fine. Basically you need a very small poweramp.
Googling on "headphone amp" might help.

[michael_krell]

THanks i understand that but what im asking is if i need to use a voltage to current converter converter with an output impedance of 150 ohms. Im pretty sure thats it im going to try that.

[SaBer]

I just made one of these
http://www.paia.com/hdasch.pdf
http://www.paia.com/hda.htm

Works very well with my akg k240M headphones, which are pretty demanding. I coul hear a clear difference in clarity, when I took the signal straight out of a discman, compared to the signal from the discmans line-out through the headphone amp.

You could take just one channel, and the part-count would be 8. That's the simplest headphone amp I found on the net.

[Joe Davisson]

A simple emitter-follower (current amp) works well as a headphone driver, here's some specs on the one I made using a 2N3904:

C - 9v
B - 15k/100k bias
E - 100-ohm, 1W
22uF output cap from emitter

Bias so the emitter is near 4.5v. Drive with a pedal or simple preamp, since there's no voltage gain here. It wastes power, and the 100-ohm resistor might get warm. It's easy, but probably not great for battery use.

[michael_krell]

I used the opamp circuit shown and it works, but not really the way I want. When the gain goes up just a little bit the wave distorts like crazy. Im sure its a problem with output impedance, because its only when theres a load that it changes.

[SaBer]

The problem  shouldn't be with output impedance, beacause I could successfully drive my 16 Ohm earbuds and 600Ohm K240M:s with it.

Wich opamp are you using? Not all are able to drive loads like that.

What about your input signal? I got strange distortion, if I used a "headphones" signal, but it got clean when I switched to line level.

It could also be your power supply. How many volts are you using?

[michael_krell]

i think you are correct about the opamp, a higher powered opamp would probably work better. the input signal is coming straight from a delay chip. pt2399 to be exact. the input signal from that is going to be headphone level. Do you think i should attenuate that signal? my power supply is a +and- 12V supply. it has plenty of headroom for this application i think.

[SaBer]

Try first replacing the opamp.
If the signal didn't clip at low levels, the input shouldn't be overloaded, so probably no need to attentuate the signal.
The  power supply should be ok.