Hiraga "le monstre"

[wahab]

Originally Posted by WuYit

masag1,
I would try to avoid that capacitor, would rather reduce the resistor value from 220 to 100 Ohms (or more).

LuYit, you are totaly wrong...
Reducing the FB resistor will increase overshoot.
Either increase it, but then THD rise, or compensate by paralleling
it with a cap as little as possible connected in serial with a resistor...

[WuYit]

wahab,
on top of that, to make everything even more irritating, I would also try to decrease the open-loop gain.

[WuYit]

masag1,
what´s wrong with polystyrene? Have you actually used the 2SA1407/2SC3601? What have you learned from building 10 amps?

[WuYit]

wahab,
this is an unusually pure, fast and stable design even with heavy loads without polluting capacitors in any location, I would not worry much about overshoots.

[wahab]

WuGit,
It s a reasonnably power hungry class A amp,
but not really my cup of tea THD wise, though the amp
i use has about the same power....

Diy audio popular amps simulations

[a.wayne]

Originally Posted by WuYit

wahab,
this is an unusually pure, fast and stable design even with heavy loads without polluting capacitors in any location, I would not worry much about overshoots.

Overshoot ( ringing ) is very much a stability problem, being only 8 watts it is not a big deal , like a small fire cracker going off when the smoke come out


Wahab:

Does the actual measured response look the same as your sims ?

[osscar]

Here's a small ringing at 160KHz (sorry about picture quality ). It was measured in test version where output transistors connected to PCB with wires.




According to some books this output type may have a slight degree of instability.
I will try to repeat measurement in final version.

[masag1]

Originally Posted by WuYit

masag1,
what´s wrong with polystyrene? Have you actually used the 2SA1407/2SC3601? What have you learned from building 10 amps?

What I have learned?

The 8Watt is very easy to build, and a stabile, reliable amp. My first one is 18 years old and still working in my equipment.
I never had to readjust offset. The only thing was to resolder the joints, yeah, 18 years of work do some changes in the crystal structure of the solder.

All the other 8 Watt amps are still working, giving fun to my friends.

Using the 2SA1407/2SC3601 as drivers allowed me to reduce the compenstion cap frm 2nF to 1nF, but sound was not sufficient, maybe we have to adjust the currents.

We are in work with a vesion, that has an CCS at the input. So we don`t have to look for the GR Idss J-fets, and we can play with the current.

Regards

Sam

[a.wayne]

Originally Posted by osscar

Here's a small ringing at 160KHz (sorry about picture quality ). It was measured in test version where output transistors connected to PCB with wires.




According to some books this output type may have a slight degree of instability.
I will try to repeat measurement in final version.

Oscar can you show @ 20 ,1K,20K, 50K, 100K it would be interesting to see square wave response in the audio band.

[osscar]

Hi,
20kHz can be seen in a few posts back, but i will try to remeasure these F today!