The Ping-Pong VAS

[Stee]

see what happens with the copy and paste

 

[kubeek]

I don´t see it.

 

[Stee]

see now

 

[darkfenriz]

The schematic is wrong.
Output stayes at around 1.4 V.
Also such a "spring" between collectors usually results is stauration of one of transistors.

Adam

 

[megajocke]

The "STD VAS" won't work correctly either. The upper part half of the circuit can't swing negative and vice versa.

 

[darkfenriz]

true

 

[Stee]

Figure 2.5 - A Typical Direct Coupled Transistor Amplifier

see this that i have copied
http://sound.westhost.com/amp-basics2.htm


and this about input
http://www.esafono.it/a700.pdf

 

[BV]

Again wrong schematic. Try it this way..

 

[Stee]

Many thanks BV -->Very GOOD

you are a little genius

divide the functions is the best strategy
compensates for the differences effectively

in the current stage need just put other two LEDs on input
maybe need also two capacitors like A700 diy gene

your simulator can also put resistor's value?

 

[BV]

Stee, we are reinventing wheel or ligt bulb , it is nothing new on schematics.
Of course simulator can put values,
http://www.spectrum-soft.com/index.shtm
download, try it and learn to use.

 

[kubeek]

And when you get to know it, download the russian version with all components all possibilities of simulation

 

[Stee]

Thanks a lot

i will try

maybe it's not new
but i never seen that double local NFB in one commercial amplifier

 

[BV]

Amplifier called "Texan", about 1975. Date in picture is not "date of birth".

but i never seen that double local NFB in one commercial amplifier

Maybe because it is not worth to use it...

 

[megajocke]

I believe it has been used but most have abandoned it because of its extremely poor thermal stability and tendency to spontaneously blow up.

 

[darian]

I don't think there is quite nothing new in these. You can look at the F5 from Pass which uses the exact same feedback scheme in his CFP output.
Actually, I am not sure it has any sort of advantage over the kind with only one feedback path in the middle. The simulation can tell if it's better or not, try it and let us know Stee. By the same way you can determine if putting emitter followers after the CFP is interesting distortion-wise, but I don't think it is since the gain is high enough in the usual CFP.
And after all, the best way to do a CFP could be with a total feedback (plain wire). Who really needs gain in the final stage? If you really want a gain of 4 after your opamp, you can also use a common base stage in between like in the musical fidelity amps.

http://www.diyaudio.com/forums/attachment.php?s=&postid=673432&stamp=1120201026

 

[Stee]

another OPA can solve this problem?

Hello to all

the purpose is not to set a gain (forcing a ratio on VAS)

the aim would be regular distinctly two branches (rails)
before they are added in the current stadium (stage)

to obtain two identical gains...

maybe use the primitive NFB is not a good idea
can solve this an operational from VAS
that can make difference and send result on input OPA?

 

[Stee]

RESUME TEXAN

re-design of TEXAN - thanks BV