Mosfet Headphone Amp

[Antoinel]

Here's an improved circuit from 1976 ; except with BJTs for output.

[sgrossklass]

That's the "cascode" variation, which IMO stands a better chance of working well as the impedance seen by the opamp on its rails is much lower. As a further bonus, Vcc and Vee can be chosen higher than the opamp's maximum ratings, since the opamp is kept at lower supply voltages.

[44250]

Today i started this...

[routhun]

Don't see any MoSFETs in the board, did you build circuit from the same schematic?

[44250]

There will be,today when i buy them! There are holes for them on a pcb if you look closer and you can see on second and third picture where they will be.

[sgrossklass]

Are you sure you really want to load a TL07x with 220 ohms?

[44250]

Originally Posted by sgrossklass

Are you sure you really want to load a TL07x with 220 ohms?

--->...over 1k2 in both rails of supply? I don´t know much about theory but i will try. I beleve in APEX designes just because i have built four of his ampolifiers (Ax12, NX16, HV23, G100) and a few other things (dc-overload protect + clip psu,ne555 protect,A-class shunt 2 x 24V,regulated PSU10,) and know about many other that work just fine (SR200, F100, AX14, A75, D14, auto range VU and clip indicator...) . That was enough for me to trust in all other of his designes so in this one too. I will try it these days,my job and my private obligatons don´t give me enough time just to put it inside the Standard preamp and to conect it to a +/-12V (to try it) ,it is allready assembled. When i finish it,i will try it with headphones and use it with an amplifier connected to an output just for others to hear how the amp sounds on a regular preamp and than on this head-amp. I don´t know no other way for other to hear it...

[44250]

I have tried it today,but i made a big mistake because i didn´t put 47k trim.pot as it is shown in a schematics. I haven´t payed enough attention and that cost me output fets BS170,resistance of 47k trim.pot works along with adjusting volume as a connection of a TL071 negative feedback to the ground,so there was a big dc-offset at the output and my capacitor got very hot and almost exploded,luckely i have noticed that in time. Than i put MPSA92 / 42 instead BS250/170 AND IT WORKED! It sounds just fine but BJT´s are also getting very hot because they get too much base voltage. To get it to work in a BJT regime i beleive that 1k2 resistors in a power rails should be replaced with smaller resistance,and 220R load with a larger resistance. That is something that i don´t know to do quite well so i will rather buy a new pair of BS170 and do it again. What it matters is that this thing works,and that i have found a mistake that i made. Hope no one will do it after my experience!