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Old 3rd February 2005, 03:28 AM   #1
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Talking 22W OTL amplifier circuit


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:
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Old 3rd February 2005, 03:42 AM   #2
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Default Old audio book

Read also new audio books - with five devices you can't make miracle, although many people claim it .
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Old 3rd February 2005, 04:13 AM   #3
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Default Re: Old audio book

Quote:
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
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Old 3rd February 2005, 04:25 AM   #4
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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 .
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Old 3rd February 2005, 04:41 AM   #5
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Quote:
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

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Old 3rd February 2005, 07:21 AM   #6
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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.
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Old 3rd February 2005, 07:55 AM   #7
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Quote:
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
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Old 3rd February 2005, 08:03 AM   #8
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To Winco : I agree with you , higher gain, but lower SR, higher distortion at " high ".
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Old 3rd February 2005, 07:28 PM   #9
edl is offline edl  Hungary
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Hello Darkside!

So nice diagram! Looks like JLH's topology. I like them!
(Anyway I much prefer BJT's.)
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Old 3rd February 2005, 07:37 PM   #10
edl is offline edl  Hungary
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Ohh...sorry!!!

Not Darkside...

Darkhorse!
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