Searching simple BTL approach

[gruni]

Hello everybody
i'm searching for the simpliest possible btl approach. i thought of just adding a second VAS and output stage to an existing amplifier design's differential amp non-inverting output. would that be possible? what feedback would be necessary? or is there an even simpler possibility?

i hope you can help me!

 

[mjf]

hello.
balanced or unbalanced inputs?
nelson pass has some designs .......
e.g. you can use a differential amp as a converter unbalanced to balanced and connect a power stage with it.............
greetings.............

 

[gruni]

unbalanced input to bridge output. so i can use one long-tail-pair as the input, feeding two seperate VAS + output stage, one on the inverting output and one on the non-inverting output of the long-tail-pair? if so, do i have to feed the output of the second VAS + output stage back to the LTP and how do i calculate it?

if it's not clear what i mean i could make a schematic...

 

[AndrewT]

I think one (or more) of Kleinschmidt designs use something similar.

There are others posted on this Forum.

 

[mjf]

hello.
something like this...........
the opamp is a symbol for a (inverting) vas+output stage.
this is only a suggestion on principle...........do not know how this sounds and so on...........
greetings...........

 

[gruni]

the input stage meets my imaginations. but i thought of running feeback back to it, your schematic uses local feedback, doesn't it?

 

[mjf]

ja,das ist eine von mehreren möglichkeiten........andere mit über-alles-gegenkopplung müsste ich erst suchen.....
grüsse...........
transl:
yes,one of some possibilities..........others i would have to search for............

 

[gruni]

würde die sache natürlich einfacher machen, aber ich glaube wir halten das ganze auf englisch, auch wenn mein englisch zu wünschen übrig lässt

i drew two possibilities of feedback. i used quasi-complementary output so i don't have to adjust the schematic later, because i will use them in the final amplifier.

the first file shows local feedback over the vas and the output stage, the latter shows global feedback

 

[gruni]

second file

 

[mjf]

hallo.
there is a suggestion for a little adaptation of the output stage.
the (little,sorry) picture shows the typical design of many wellknown outputs like naim 200 and so on...........
grüsse............

 

[djk]

 

[gruni]

i built my global-feedback approach i posted above. with that solution i get no output at all...

 

[mjf]

hello.
does the simulation work,is it o.k.?
grüsse.............

 

[mjf]

and it looks like there is a little mistake in the schematic - the psu supply line is connected on the positive side -
once at the psu
and on the other side at the res after the psu........
grüsse...............

 

[gruni]

yeah that was a mistake but in my assembly i did it right by instinct

well i havent simulated it yet, perhaps i should do this