No Miller cap, Double bootstrapping amp.

[GEirin]

Hi all.
I´m new in this forum and is my 1º post.
In 1988, i build my 3º amplifier (50W). The amplifier is class B, had differential input, no Miller cap, double bootstrapping and quasi-complementary design.
I want to build a newer amplifier, or no.
My questions
1º, What is your think about the attached schematic amplifier.
2º, I modify my amplifier, or build a new amplifier ( P3A.......)
I need your help.
Thanks
Guillermo Eirin

 

[GEirin]

Sorry.
My schematic amplifier.

 

[thanh]

hi! what's is the function of R2 C2?
and R13 R11 C7?
and R24 R17 T5 T6 T7 T8

 

[MikeB]

Sorry.
My schematic amplifier.

Hmm, i have no word for windows...
Can you upload grafix ?

 

[thanh]

png file

 

[MikeB]

thanx Thanh !

R2/C2 is a classical RC, in my opinion the better alternative for
feedbackcompensation than cdoms.

Mike

 

[thanh]

really?

 

[MikeB]

Yes ! (For me)

My latest amp uses these, i am very happy with it.

FYI:
http://www.diyaudio.com/forums/showthread.php?postid=501188#post501188

 

[MikeB]

Hi GEirin !

Why do you want to build new one ?
Do you have some specs about yours ?
How does it sound ?

Mike

 

[thanh]

mikeb! in computer ,my amp is stable with 100p from vas to -input but in real world my amp always ocssilates .i also use your method ,200p without resistor and the result isn't also better
in simulator , no use miler capacitor is intersting for me

 

[thanh]

mikeb! your ltp use two resistor load but geiirin only uses one resistor load
do the result become better ?

 

[lumanauw]

Hi, GEirin,

Nice idea. Whats the concept of using double bootstrap in the first place? What do you wanto to achieve?

 

[MikeB]

Hi thanh !

With the 2 resistors in LTP the RC is doubleeffective, in theory...
I think 100p from vas to -input is way too much, try 10p...
You also need caps from vas to gnd. (best with RC)
And it seems, in real world bjts are much slower than in sims, and
capacities between wires changes a lot...

Mike

 

[thanh]

thank mikeb!

 

[GEirin]

Hi all.
Thanks.

MikeB.
My amplifier is very old (1974?), quasi-complementary desing. The sound is good. I need to improve. Recenty, I look Aksa, P3 and other amplifiers, ( no constant current source) and i think, my amplifier is good?.
Ok. Yes, is quasi-complemtary. And i think in complementary. Also in class AB.
My amplifier had no miller cap, is good?
My amplifier had two bootstrap, is good?
What is your opinion?

Lumanauw
I am Industrial Designer, no electronic engineering. I believe that the amplifier is original Philips design.
My amplifier had: 50W, +/- 35V. T11 and T12 2N3055.
My idea is to change output transistors.

 

[GEirin]

Hello Thanh.

R13, R11,C7 and R7, R8, C8 are double bootstrapping.
R24, R17, D3, D4, T5,6,7,8 are protections circuit.

Guillermo Eirin

 

[lumanauw]

Hi, GEirin,

I also found out that bootstrap sounds better than CCS. Is this why you want to make it double bootstrap?
I have "suspicion" that double bootstrap that you draw cannot make positive signal well. Negative is no problem, since it is drawn by VAS transistor. But how about up positively?

 

[GEirin]

Hello Lumanauw.
Many amplifers has single bootstrapping. I want to learm why my amplifier has double bootstrapping. Pros and cons.
Guillermo Eirín.

 

[darkfenriz]

hi GEirin
first impressions are nice as I look on schematic
I don't think you need a miller cap; C6/R1/R4 circuit seems nice way to keep the amp stable, also R2/C2 is useful, so you can have no oscilations at all
But i would skip R9/C9 - unneeded phase distortion is never good.
About the second bootstraping cap- I don't see a point in using it as voltage-amplifying transistor is opened and can give much current. The compensating cap is useful, when this transistor is nearly 'closed' (sorry for my english). But maybe this makes the situation better.

As your main question was about copying this or not:
my answer is: yes, after some changes you will have much fun, good sound and SATISFACTION of having self-designed amp.

What I would change:
skip R9/C9 as mentioned before
use non polar 1u good quality C1
use complementary output with some modern bjts
mirror T1,T2,T3- two complementary dirrirential stages with double bootstrap....may be interesting, don't you think?

regards
cheers

 

[GEirin]

Hi Darkfenriz.

Thank you for the explanation. What is your opinion the C5?

Thank you for the recommendations. But think to improve the transistors, and to change quasi-complemtary for complementary design.
Now, I think other new amplifier. A symmetrical amplifier with double bootstrap? humm.....

Guillermo Eirín