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-   -   4w All Fet Class-a Amp (http://www.diyaudio.com/forums/solid-state/58380-4w-all-fet-class-amp.html)

DarkHorse 2nd June 2005 08:32 AM

4w All Fet Class-a Amp
 
2 Attachment(s)
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);

;)

Upupa Epops 2nd June 2005 09:35 AM

4 W amp with 1.1 bias current ? What are you waiting from this " miracle " ?

triode_al 2nd June 2005 10:52 AM

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.

padamiecki 2nd June 2005 12:46 PM

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

DarkHorse 3rd June 2005 08:53 AM

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

DarkHorse 3rd June 2005 09:00 AM

Re: Re: 4w All Fet Class-a Amp
 
2 Attachment(s)
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:



;)

Upupa Epops 3rd June 2005 09:04 AM

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 ;) .

DarkHorse 3rd June 2005 09:24 AM

2 Attachment(s)
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)..

Fuling 3rd June 2005 09:27 AM

Note that the original circuit is a transconductance amp (current feedback).

DarkHorse 3rd June 2005 09:34 AM

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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