3W Pure Class-A AMP

[Graham Maynard]

Hi Darkhorse,

Please don't think that I am picking on you personally, but I so often see 'simple' circuits like these.

Yes (Post 10) will work, and it has simple internal ac and dc feedback, but ......... nobody ever seems to comment on the fact that the control of loudspeaker back emf is asymmetrical, and thus the amplifier's output is liable to become characterised by the crossover/loudspeaker combination much more than is the case with an output stage that is capable of *actively* conducting both positively and negatively.

For example there can be a hefty NFB controlled positive current flow via M1, but only the current due to (1 + 6.8 + speaker) ohms flowing negatively.


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

[DarkHorse]

Originally posted by Graham Maynard
Hi Darkhorse,

Please don't think that I am picking on you personally, but I so often see 'simple' circuits like these.

Yes (Post 10) will work, and it has simple internal ac and dc feedback, but ......... nobody ever seems to comment on the fact that the control of loudspeaker back emf is asymmetrical, and thus the amplifier's output is liable to become characterised by the crossover/loudspeaker combination much more than is the case with an output stage that is capable of *actively* conducting both positively and negatively.

For example there can be a hefty NFB controlled positive current flow via M1, but only the current due to (1 + 6.8 + speaker) ohms flowing negatively.


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

hi,Graham Maynard :
that is realy matter what your said,I will be back tomorrow,
..sorry!haha..time to off duty now..
happy!

[PMA]

The circuit shown may serve as a "starting point" of the newbie el. designer. After he sees all the design flaws and problems he may move to higher circuit league - in this case the attempt would be valuable.

[DarkHorse]

Originally posted by PMA
The circuit shown may serve as a "starting point" of the newbie el. designer. After he sees all the design flaws and problems he may move to higher circuit league - in this case the attempt would be valuable.

hello,PMA:
haha...your word is funny and exactly,I don't feel any unsuitable
in this schematic,but I know if the amp runs,it's result will make me know more about the true!I will kept trying..
regards,
WINCO

[DarkHorse]

perhaps,this circuit form is more fit to be preamp or headphone amp..
it's too low efficiency,when as a power amplifier..
and it hard to using constant current source instead of resistor..
here is the schmatic (author is our master:Nelson Pass) which I got it from internet,the main circuit form same as mine,but it is a preamp circuit:

[Upupa Epops]

If you can easy to build amp, try PMA's " Mosfet follower ". Many positive references on this forum . Efficiency of this connection is more better.

[DarkHorse]

Originally posted by Upupa Epops
If you can easy to build amp, try PMA's " Mosfet follower ". Many positive references on this forum . Efficiency of this connection is more better.

hello,Upupa Epops ,PMA:
I have checked "MOSFET FOLLOWER",but find nothing..Wowo..
can you do me a favour to show this thead where?

best regards,
WINCO

[Upupa Epops]

Look at www.pha.inecnet.cz/macura/audiopage.html - Mosfet Power Follower.

[DarkHorse]

Originally posted by Upupa Epops
Look at www.pha.inecnet.cz/macura/audiopage.html - Mosfet Power Follower.

wah..PMA is an great designer!I fell so surprise when visit the link
which is offered by Mr.Upupa Epops,thank you two!
here is PMA's "mosfet power follower":

[DarkHorse]

here I have draw a circuit same as PMA's,but it's not easy to
regulating the out point voltage to 1/2Ucc,maybe need a high power resistor to help..perhaps,I will build it next..
and I will not give up with"3W Pure Class-A AMP",very eager to
do something for it (lastest version is 4W)now..