Discrete simple headphone amp

[kubeek]

I already posted it in the chip amps section, but I didn´t have too many helpful answers.
So could someone please comment on this circuit?
here

+-9V, 16-600ohm load

thanks

 

[djk]

Looks like it needs a bit of work.

You should probably have a zobel on the output.

Don't forget to use compensation on the NE5534, I would use the NE5532 instead.

You don't need driver transistors.

Here is a headphone amp from an older top-of-the-line McIntosh preamp.

http://i56.photobucket.com/albums/g196/dkleitsch/C32.jpg

It looks a bit like the AKSA power amp without the outputs.

 

[kubeek]

I don' t need too good amp, I need only something cheap (I will make 4 stereo drivers) with enough power and voltage for wide range of loads, and not as bad as LM386.
Driver transistors are the 2N..? I simulated distortion, and it came out better with them.

The choose of transistors is because I have enough of them from some recent project, but will BCxx and BD139/140 make a difference?
And what about TL072 instead of the NE5534/2?

What values of zobel do you suggest for headphones?

 

[Gordy]

For reference...

A project something like your project:
http://headwize.com/projects/showfile.php?file=eaton_prj.htm

The circuit diagram from that project:
http://www.headwize.com/images/eaton2.gif

Other interesting reference projects:
http://headwize.com/projects/index.htm

 

[kubeek]

I just found out that my behringer mixer uses two 4580s + 100ohms paralleled for headphone out, so I guess almost anything will be better than that.

 

[djk]

"The choose of transistors is because I have enough of them from some recent project, but will BCxx and BD139/140 make a difference?
And what about TL072 instead of the NE5534/2?"

The 5534/32 sounds quite a bit better in the mids and bass than the TL07X opamp in this circuit.

"What values of zobel do you suggest for headphones?"

It has nothing to do with the headphones, it is for amplifier stability. I generally use 0.1uF and 10 ohms.

The Eaton2 looks like a good project. The MJE243/253 are much better devices for outputs than the MJE340/350.

 

[Bonsai]

Suggestion: use an off the shelf buffer like an LT10 or similar if you want something simple with good performance.

Take a look at the LT website.

 

[kubeek]

No LT10 or mje243/253 in here

 

[djk]

Use what you can get, the MJE340/350 are good up to about 100mA when warm.

Should be good for over 120dB on most headphones.

 

[Leolabs]

Try 2SB647/2SD667 too.

 

[Gordy]

No LT10 or mje243/253 in here

I think Bonsai meant LT1010.

See the first figure on the LT1010 datasheet: LT1010 + LT1056 + LM334 = instant headphone amplifier (just add potentiometer and 18Volt power supply).

 

[kubeek]

I fugured that out too, but LT1010 costs here cca 6 bucks, so I will probably stick with the opamp + discrete buffer version, which is a way cheaper solution.

 

[jacco vermeulen]

Even cheaper, skip the diodes and have the output of the opamp on the emitters of the driver devices.

 

[djk]

"Even cheaper, skip the diodes and have the output of the opamp on the emitters of the driver devices."

Skip all that and have the opamp drive one output, and use a voltage regulator as a constant current source.

 

[jcx]

some relatively common headphones can require over 100 mA peak current to reach realistic spl

most older (available in PDIP) op amps can't drive that much current and require output current boost/buffers

but there is little need for darlington level current gain

a single ef with Class A ccs bias should be fine as output buffer inside the op amp feedback loop

 

[djk]

Any good opamp can deliver 10ma, drive an output with a Beta of 50, you can drive 500mA peak.

Build an Aleph type current source and set it to 200mA, it will be able to provide 400mA peak.

Run it all on ±10V, the output and current source will both dissipate 2W, and be able to drive 1.25W class A into 16 ohms.