22W OTL amplifier circuit

[DarkHorse]

hello,do you like OTL amplifier?
using MOSFET as output devices?
suitable output power for your room?
hi-fi sound?
I read some old audio book,looking for a easy to build and sounds good's amplifier circuit...I choose the classical OTL amp.
so I do simulating with the BJT output stage version!the result isn't well,too large of the distortion...I know the reason is simple circuit construction has no more driver stage to offer more driven current...I think of MOSFET power device,haha...
after many times I do simulation and adjusting the parameter of the electrical devices,I got more satisfying result:
50V single power supply,class-AB,input sensitive is 850mV(RMS),22W(RMS,8ohm load) output power,from 20Hz~20KHz THD=0.023%(full power output).
well,let's see the circuit schematics:

[Upupa Epops]

Read also new audio books - with five devices you can't make miracle, although many people claim it .

[DarkHorse]

Originally posted by Upupa Epops
Read also new audio books - with five devices you can't make miracle, although many people claim it .

yes,I know that...but I don't feel the new audio book has new and good idea,few years ago,I order a lot of audio book from the post,but now I don't do that again,lost interesting,too little readable knowledge,so I would like to read old book...

regards!
WINCO

[Upupa Epops]

Winco, knowledges aren't about feeling, but about knowledge of theory and about practical experiences. Sure, old books are good too, but not in all .

[DarkHorse]

Originally posted by Upupa Epops
Winco, knowledges aren't about feeling, but about knowledge of theory and about practical experiences. Sure, old books are good too, but not in all .

ok,Upupa Epops:
I understand your meaning!I will try my best to chase up the times development! a old word:"men live to old and lean to old!"
is it?
thank you!
regards!
WINCO

[Graham Maynard]

Hi Darkhorse,

When you go from bipolar to Mosfet you don't need the biasing resistors to be so low.
Try R6 and R7 at 1k each + readjust RP2
Try 2N5551 for BD139
Try increasing R2

Increasing the R2/R8 ratio increases the open loop gain to limit of Q2 loading
this can decrease closed loop distortion - find optimum

This type of input stage needs a low source impedance
preferably 50 ohms, not more than 600.

Enjoy your dabbling.

Cheers ......... Graham.

[DarkHorse]

Originally posted by Graham Maynard
Hi Darkhorse,

When you go from bipolar to Mosfet you don't need the biasing resistors to be so low.
Try R6 and R7 at 1k each + readjust RP2
Try 2N5551 for BD139
Try increasing R2

Increasing the R2/R8 ratio increases the open loop gain to limit of Q2 loading
this can decrease closed loop distortion - find optimum

This type of input stage needs a low source impedance
preferably 50 ohms, not more than 600.

Enjoy your dabbling.

Cheers ......... Graham.

hello,Graham:
in fact,I don't agree with you in "Try R6 and R7 at 1k each ",the power MOSFET need high Iq of driver stage,because of it's input capacitor is about 1400~1700pF...
but I will try with your suggest ,thank you!
I will show you the simulating result tomorrow...
regards!
WINCO

[Upupa Epops]

To Winco : I agree with you , higher gain, but lower SR, higher distortion at " high ".

[edl]

Hello Darkside!

So nice diagram! Looks like JLH's topology. I like them!
(Anyway I much prefer BJT's.)

[edl]

Ohh...sorry!!!

Not Darkside...

Darkhorse!