AW: VCS3 on the bench

[Haible Juergen]

> I keep thinking that I must be missing something.  Why did the 
designers
> connect the speaker returns through the supply?  Has anyone else 
made this
Ø	observation and modification?

I don't know if you mean the same thing I've come across recently, but 
I was more than surprised
that a 741 with its +input (pin3) tied to the negative supply (pin4) 
 could work at all - it's completely
ot of its intended common mode range.
Obviously, it works nevertheless. As far as I understand, it works 
like this: One half of the 741's
input differential amplifier is completely disabled (so it's no real 
opamp anymore), *but* the path
from the -input to the voltage gain stage still works, and so you 
still can construct some weird negative
feedback loop around the chip. Ok, you need some level shift (done 
with a pnp), and external
compensation capacitor (rather large one, obviously) - but it works.
The Synthy A MkII output amps are some of the most unbelievable 
circuits I've come across in my
life. I would have sworn it couldn't work, until I actually checked 
the pcb of a working one ...
I crosspost this to DIY - maybe someone there can add something ...

JH.