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Old 2nd June 2005, 09:32 AM   #1
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Question 4w All Fet Class-a Amp

hi:
have a look with this circuit diagram,can it works well?
I draw this circuit diagram last night...
RP1 control the currency of output stage,set it to 50K at first;
RP2 control the voltage of ouput point(0.22V+1/2Ucc);
SK170 can replace with sk389 or NPD5564(twins);

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Old 2nd June 2005, 10:35 AM   #2
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4 W amp with 1.1 bias current ? What are you waiting from this " miracle " ?
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Old 2nd June 2005, 11:52 AM   #3
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Default Re: 4w All Fet Class-a Amp

Quote:
Originally posted by DarkHorse
can it works well?


I'd take the gate resistor R8 of the top IRF510 higher --> 510k too, and add a gate resitor >> 10 ohms.
The input/driver will have reduced distortion as you take a higher Vb there, say 50V. This might be a considerable reduction. It is also something that the feedback in the way you design it, cannot correct. This means that RP1 has to increase along the way.
It does have a Pass flavour to it that is nice. Its simple. What do we want more? Well, Q4 is not really needed, and by having a resister it should work out well too methinks.
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Old 2nd June 2005, 01:46 PM   #4
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Default Re: 4w All Fet Class-a Amp

Quote:
Originally posted by DarkHorse
hi:
have a look with this circuit diagram,can it works well?
I draw this circuit diagram last night...
RP1 control the currency of output stage,set it to 50K at first;
RP2 control the voltage of ouput point(0.22V+1/2Ucc);
SK170 can replace with sk389 or NPD5564(twins);


it is fet/mosfet version of Aikido Amplifier by John Broskie, TCJ
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Old 3rd June 2005, 09:53 AM   #5
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Quote:
Originally posted by Upupa Epops
4 W amp with 1.1 bias current ? What are you waiting from this " miracle " ?
hi,Upupa Epops :

4W(RMS) is 8W(peak)in sine-wave ,so load is 8ohm,and P=I^2*R,then I=1.0A,so I=1.1A is suitable!
driver stage using SE instead of using bootstrip or using hight-Voltage supply,and it can win more low distortion...

cheers
WINCO
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Old 3rd June 2005, 10:00 AM   #6
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Default Re: Re: 4w All Fet Class-a Amp

Quote:
Originally posted by padamiecki



it is fet/mosfet version of Aikido Amplifier by John Broskie, TCJ
I don't know where this diagram from!but it's topology so simply that make me so surprise...
this is original schematic which I referenced:



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Old 3rd June 2005, 10:04 AM   #7
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If you take this connection as excercise, so go on. But with four transistors don't wait miracles, although they are relatively modern ones, all is too simply .
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Old 3rd June 2005, 10:24 AM   #8
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Quote:
Originally posted by Upupa Epops
If you take this connection as excercise, so go on. But with four transistors don't wait miracles, although they are relatively modern ones, all is too simply .
haha:

yes,I understand your meaning.
but as a small "kid"(only 4W output power),it's capability was enough strong,THD=0.15%,phase angle is +0.2 degree(20Hz) and -0.7 degree(20KHz).I think it is so great...
all for it's simply.I like it,and hope it's sound can sweet than ZEN2(the class-a amp I have alread build)..
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Old 3rd June 2005, 10:27 AM   #9
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Note that the original circuit is a transconductance amp (current feedback).
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Old 3rd June 2005, 10:34 AM   #10
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Quote:
Originally posted by Fuling
Note that the original circuit is a transconductance amp (current feedback).
hi:

yes,I have note this problem.
current FB is can cut-off the speaker's reverse voltage...
but distortion is too XXX(4%).

see you tomorrow.
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