Universal Headphone Amp - fits different headphones
 

Here I will post a headphones amplifier.
As told it can be used with different impedance headphones.
From 16 Ohm upto 600 Ohm.

If you have several different headphones and want to use only same headphone amplifier, this is for you.

Other features are JFET input and MOSFET output.
I know you will be pleased by this.

I be back with schematic any day now :)

......single ended or complementary?

Jam

Here you are, jam

It is a differential 2SK170BL input.
I actually use 4 2SK170. Two for the currentsources.
The output is complementary Class A using IRF610/9610.

What is special perhaps is the 100 Ohm output resistor,
this makes the amplifier fit most headphones.

The headphone amplifier shows acceptable THD.
I bet it has good second harmonic sound.
The FFT analys tells me this.

The quiescent current is 200 mA through the output.

100 Ohm output resistors or any output resistor for that matter, has no place in a high quality headphone amplifier.

You could just remove the output resistors and it would serve the original goal better, no?

Yes you could, but why put it there in the first place?

It has to do with impedance in the headphones.
With that resistor you do not have to turn the knob for different headphones.

Say you have listened with 600 Ohm headphones
and then you change to a 32 Ohm pair.
You just have to turn down the knob extremely far.

To have 100 Ohm output impedance is something that is used in such headphones amplifiers.
Not only that.
In many preamplifiers there are such resistors.
At the output.

The damping factor is very low in this amplifier.
But for such precise gears as headphones this does not matter much.

I know why it is there, however I and many others just don't think that it has any place in a high performance headphone amplifier.

This is a bit harsh, and not 100% true.

In the past a standard for headphones was mooted with 600R impedance. It is largely ignored, but 'phones with higher impedances may actually perform better with a higher output impedance amp.

Many 'phones nowadays have impedances as low as 16 ohms. More importantly the impedance tends to vary with frequency. This leads to a frequency response which is not flat when used with amplifiers with output impedances of more than a few ohms. An output impedance of 2 ohms or less is regarded as appropriate by most designers of quality solid-state headphone amps nowadays.

Why not use a current limiting circuit? Using output resistors is cheap and lazy.