Kevin Aylward wrote:
Scott Dorsey wrote:
Kevin Aylward wrote:
Scott Dorsey wrote:
input transistors. That's, dare I say, just plain daft, and don't
work.

Its like nails scratching nails down a blackboard to us analogue
designers. There are so many reasons not to try this. Indeed, in my
current designs, there arnt any, its all current sources.

(Note that by input I was referring
to the negative-going input on the differential pair that is used
for feedback, but of course if you offset one side of the
differential pair, you offset both of them)

You also offset the output, which don't do very nice things to the
speaker.

No. There is a capacitor in the way. That's the point. You want
that offset on the capacitor.

One doesn't use output capacitors for power amps nowadays. Amps are DC
coupled. Don't know the last time I saw a single supply amp. Probable in
Dr. Who's TARDIS.

Are you listening to anything I am saying? I am not talking about an
output capacitor, I am talking about a capacitor in the feedback loop
between the output and the inverting side of the differential input
pair.

Let's go through this again:

1. If there is no offset, you don't need a capacitor

2. If the offset is larger than the signal, you use a capacitor.

3. If the offset is smaller than the signal, make it larger.

This is not anything particularly difficult here. Read the Sanyo
capacitor handbook for a description of the whole thing. Read Doug
Self's series on amp design.

However, the design is easily understood from inspection by anyone that
understands circuit design. There is no rocket science here. All the
blocks are standard stuff. The only bit that might need explaining is
the somewhat novel second feedback loop on the output transistors on one
of the circuits. Oh..and that some of the diodes are zenors for
simulation purposes.

Yes, but not being able to read the numbers makes it problematic for
use as an example circuit to point out DC setpoints.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."