The DiaPhone headphone amplifier

[Tekko]

This is a simple little amplifier i just came up with, its based onthe so called diamond buffer, or atleast i think it is.

The primary application is driving headphones but simulations show its also capable of driving a 8 ohm load to a few watts of power.

A sim of a few different impedances:
http://i.imgur.com/tepDj.png
http://i.imgur.com/aS12Z.png
http://i.imgur.com/28mbq.png
http://i.imgur.com/i7K2b.png

If this has already been done, i apologize and will take these schematics down if so is desired.

 

[sgrossklass]

Have you verified stability into capacitive loads? 10..47 nF usually get me back on the ground if distortion numbers are looking too good...

 

[Tekko]

I built it on a breadboard and it does indeed oscillate at a low level, but i have deemed this to be caused by the breadboards stray capacitance and the inductance of the wires running all over.

I used a LF356 opamp.

A video: The DiaPhone - YouTube

 

[Tekko]

Ok thats weird, a 1.5µF capacitgor across the output actually helps reduce/remove the oscillations to the point where it appears like what remains is the switching noise from the DC/DC converter i use to run off battery power.

 

[Tekko]

A stereo version has been built, and its 100% stable: http://i.imgur.com/x9cQs.jpg

Draws about 100mA per channel.

In impedances above 16 ohms, it operates mostly in class A.

Into 32 ohms and up, its pure class A.

 

[dirkwright]

It's not a diamond buffer, but that's ok. See the article by Walt Jung. It looks to me like a push pull emitter follower driving an output push pull emitter follower pair.

 

[donsolano]

the output topology is similar to the Dartzeel, i think

 

[Tekko]

I dreamt up that circuit, only relevance i knew was the diamond buffer and thus thought it was one of those.

But it is not, so i wish a moderator could remove "The DiaPhone" from the thread title.

 

[homemodder]

It's not a diamond buffer, but that's ok. See the article by Walt Jung. It looks to me like a push pull emitter follower driving an output push pull emitter follower pair.

It surely is a diamond buffer. Maybe needs slight adjustments so it can perform as good as it should.
The THD figures are dissapointingly high for such a circuit but maybe thats because of the opamp model.

 

[peranders]

The D2, D4 shouldn't be there at all.
Some useful links can be found here

 

[Tekko]

I changed the output stage into CFP and reduced the total drawn current to less than 50mA for the whole circuit.

This is what resulted: http://i.imgur.com/5HMTl.png