"Arny Krueger" wrote in message
...
"Watson A.Name - "Watt Sun, the Dark Remover""
wrote in message

Opinions on this, especially the 2.5W amp schem at the bottom.
http://www.intio.or.jp/jf10zl/EF.htm

When the amp is idle, and there's no(?) current flowing in either
output transistor because there's no forward bias, then the V drop
'resistance' of the E-B junction adds to the 100k feedback resistor,
so the loop gain increases to the open loop gain. So it would seem
that the amp would attempt to hunt in this region, possibly
oscillating?

Depends on the op amp. I stopped taking this circuit page seriously
when I
saw "741" on the upper two circuit diagrams.

The guy's a HAM, cut him a little slack, OK?

Do you know what a 741 is from the standpoint of quality audio?
Anathema!

If you keep the gain down to 10 or less, it's almost Hi-Fi. ;-)

Maybe a 1k resistor E to B on the output transistors would 'bypass'
this. Or should the amp be biased to work class AB.

It's a variation on what some designers call "current dumping".

However let's say the truth - this is an outdated, amateurish design
with no
known merits over established technology.

Well, didn't I say that I didn't think much of it? This guy _is_ an
amateur, AKA HAM. Also, if you investigate this guy's web pages, you'll
find he's enormously prolific, with gobs of schematics of circuits he's
built. In the true spirit of experimentation, you'll notice.

And you don't see this particular type of design in copmmercial
equipment, as I said. Which leads me to believe there are some inherent
disadvantages. I'm asking for insight into what these might be, not
destruictive criticism.

I have a number of schematics of audio power amps that I think have some
disadvantages which I wouldn't use. One is that the design connects one
terminal of the speaker to the Vcc, and lets DC thru the speaker bias
the output stage. This gives the same effect as bootstrapping. But it
also makes the speaker hot relative to ground, which isn't a problem if
the amp and speaker are in the same enclosure and isolated. So I would
consider this unacceptable, and use the bootstrapping method instead.