OT for Hybrid Headphone Amp question.

[leftovers53]

Here are a couple of more fleshed out versions. Apologies to Salas for completely lifting his line stage as the voltage amplifier.

 

[goldenbeer]

.. is a fet source follower not a tube. Hence the possibility of 1 ohm Zout (in simple source follower or if not some other SS buffer), hence the idea to begin with.

As I said, if you're using a fet or bjt anywhere in your amp, simply use a cap output and accept that you're building a solid state amp. Look at attached picture for a most simple (if probably not the best) topology. Adding tubes or transformers will just add cruft and not help.

Another side question is: given a tube gain stage, would there be any advantage to using an emitter follower rather than a source follower in a similar circuit for this application?

A bjt will work better with less voltage across, so can be more efficient and sonically better with the low voltages required by (low impedance) headphones.

 

[leftovers53]

As I said, if you're using a fet or bjt anywhere in your amp, simply use a cap output and accept that you're building a solid state amp. Look at attached picture for a most simple (if probably not the best) topology. Adding tubes or transformers will just add cruft and not help.
A bjt will work better with less voltage across, so can be more efficient and sonically better with the low voltages required by (low impedance) headphones.

Thanks for the circuit.

I ran across this buffer intended for speaker amp, assume it could be scaled down. Probably overkill was interested in how low the Zout is.

"Bandwidth (-3dB) is from 4Hz to 250kHz. Rise time is 1.5µs. Output resistance 0.16 Ohm. The circuit is very tolerant of different kinds of load. Input resistance is 10 kOhm (R0), but can be increased up to 100 kOhm (R4) by omitting R0. Input capacitance remains relatively high, about 1500pF."

Project 83 - MOSFET Power Follower

Your advice re tubes and transformers is duly noted but im planning to proceed with this. Feel free to roll your eyes and shake your head.

I will of course listen to it without the "cruft" along the way.

I did what I should have done to begin with, which is to email Kevin Carter the Lundahl transformer importer. His response was that this will work as I thought! He recommended the following gapped Lundahls.

"Lundahl LL2731 or for lower primary resistance the LL2754"

Though I would like to find something less expensive for initial proof of concept.

 

[leftovers53]

Is there a particular bjt you would recommend for this application? For that matter what are the specs to look for, for an optimal device in this role?

 

[leftovers53]

Actually given the low voltages and current involved. Even low impedance phones don't need more than 50 or 60ma. 25 mW, at the most for 110+db peaks (of course putting aside planars), would a small signal fet or bjt be a better choice in a follower like this?