Originally Posted by Foton
After thinking about this project I started to have doubts. It looks like I will waste a lot of power with no reason. I do not have 600 Ohms headphones either and this higher supply voltage is for a reason.....
I am slowly getting towards Szekeres then. But, the first step to get parts has been done: I got my transformers last week. So, my new question is.... what is the highest and making sense voltage to power Szekeres? My transformers are 36 Volts @ 1.5 Amps.
You can build the PRR SOL with modifications for lower voltage rails, lower current, etc.
Example, drop to about 30V rail, raise the 6ohm resistor to 50ohm or thereabouts. That should drop the bias to about 100mA. The resistors along the transistor will drop to about 1W for the 50ohm and 3W for the 120 ohm. Change the 22M resistor to 15M. You might be able to go to 24V, but not sure.
Just a guess, but that should give you a gain of about 2 or a bit more. I think it should be able to swing full gain with a source of 2Vrms. You should be able to drive 600 ohm and 32 ohm headphones without any issues. Volume might not be loud enough with 600ohms. Simulate it to be sure.
If you want, you can throw in some negative feedback. Say, a 10K resistor between the input pot and the cap, and a 50K resistor feeding back between the 10K resistor and the cap. Maybe drop the gate resistor to about 100. Drop the 150ohm resistor to about 120, and lower the 50ohm resistor to about 20. Roughly, gain is about 2 with about 6dB of NFB. Another guess, but should be decent starting points. Bias might increase a bit, maybe 150mA or so.
With Szekeres, put a CCS on it, should work better. You should be able to go to 12V rails with the Szekeres.
Edit: Here's a variant of the SOL, since I mentioned a CCS on the Szekeres. It's Nelson Pass's Zen amplifier modified to be headphone compliant, using an active current source. It's basically the SOL with a current source on top. http://headwize.com/?page_id=105
Edited by holland - 9/20/13 at 12:05pm