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Old 28th December 2010, 02:21 PM   #681
wahab is offline wahab  Algeria
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Quote:
Originally Posted by WuYit View Post
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...

Last edited by wahab; 28th December 2010 at 02:24 PM.
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Old 28th December 2010, 02:39 PM   #682
WuYit is offline WuYit  Sweden
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wahab,
on top of that, to make everything even more irritating, I would also try to decrease the open-loop gain.
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Old 28th December 2010, 10:28 PM   #683
WuYit is offline WuYit  Sweden
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masag1,
what´s wrong with polystyrene? Have you actually used the 2SA1407/2SC3601? What have you learned from building 10 amps?
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Old 28th December 2010, 10:30 PM   #684
WuYit is offline WuYit  Sweden
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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.

Last edited by WuYit; 28th December 2010 at 10:33 PM.
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Old 28th December 2010, 10:57 PM   #685
wahab is offline wahab  Algeria
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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
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Old 29th December 2010, 12:28 AM   #686
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by WuYit View Post
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 ?

Last edited by a.wayne; 29th December 2010 at 12:32 AM.
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Old 29th December 2010, 05:54 AM   #687
osscar is offline osscar  Latvia
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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.

Click the image to open in full size.


According to some books this output type may have a slight degree of instability.
I will try to repeat measurement in final version.
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Old 29th December 2010, 06:25 AM   #688
masag1 is offline masag1  Germany
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Quote:
Originally Posted by WuYit View Post
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
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Old 29th December 2010, 06:45 AM   #689
a.wayne is offline a.wayne  United States
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Originally Posted by osscar View Post
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.

Click the image to open in full size.


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.
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Old 29th December 2010, 07:25 AM   #690
osscar is offline osscar  Latvia
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Hi,
20kHz can be seen in a few posts back, but i will try to remeasure these F today!
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