Will this work as audio amplifier?

[thanh]

Oh! Mike! I known your method .IF, you simulate symmetry circuit, adjusting offset is a hard thing

[lumanauw]

Thanh!
What is the summary of your Hawksford thread? Is error correction a good thing? You got masters there, like Pass, Steven, etc.

[thanh]

I simulated it with 1khz signal input but It is useless. I will do it with 20khz

[thanh]

2nd ,3rd is the most important thing

[thanh]

continue

[MikeB]

Originally posted by lumanauw
Hi, Mike,
Please do so in Sims. I also want to look at the effect of 220K parrarel with Cdom. I have found one commercial unit (quite expensive) that do this.

I think it has to do with gain-bandwith product. Make amp with high gain, but low bandwith or we can create moderate gain but have wide bandwith.

Hi lumanauw !

I tried a little with these resistors, and they do have a great impact
on openloopbandwidth. Without global feedback, the bandwidth
got 5 times better. In my ckt i used 1Mohm, with these resistors
i had nearly the same bandwidth as with 220k, but not that big loss
in gain. It's like always... The less gain, the more bandwidth. :-(
But the overallperformance of the amp didn't get better, because
with global feedback i had still more gain at 20khz without the
resistors than with them.
Measurements didn't get better, but listening has still to be done...
It seems that for an amp with global feedback, you can't just look
at openloopbandwidth. Maybe my method i told to thanh is not
correct. I've read in another thread that Dr Leach said once that
openloop bandwidth is not that important, that's its the "gain-bandwidth"
that matters. But Nelson Pass does not agree. So its up to my ears
to verify what's better for me.

Mike

[lumanauw]

Hi, Mike,
Yes, calculations or SIMS doesn't always give a clue about audible sound. We just have to listening-test for knowing.
Lets see 2 amps that have very different gain/bandwith and both have marvelous sound. They are Aleph (low OL gain) and AKSA (high OL gain). So what is making good sound?

Thanh!
What sims sweep are you attaching? For error correction or other sch? They seems not have pattern.

[thanh]

That is the sim of my amp without error correction
In orcad ,you can "zoom" FFT to view easyly

[thanh]

I've read in another thread that Dr Leach said once that
openloop bandwidth is not that important, that's its the "gain-bandwidth"
that matters

Leach sai that "TIM cannot occur if the open-loop bandwidth is greater than the signal bandwidth"
http://users.ece.gatech.edu/~mleach/lowtim/bckgrnd.html

[MikeB]

Originally posted by thanh

Leach sai that "TIM cannot occur if the open-loop bandwidth is greater than the signal bandwidth"
http://users.ece.gatech.edu/~mleach/lowtim/bckgrnd.html

Hi thanh,

Thanks for the interesting link !

It inspired me to do some "mesurements" in spice, to compare
my amp with the leach. Of course this comparison is not the best,
the amps differ much in power. (120Watt into 8 ohm to 55Watt into 4ohm)

The results:

Phaseshift at 20khz:
Mine has 1.85° before coil, and 10.5° after coil, maybe i should
reduce the coil ? (It's purpose is to protect against capacitive loads)
Leach is 8.8°

Bandwidth:
Mine has a drop from 33.394db to 33.287db. That's about the
same value like the Leach (~-0.1db @ 20khz)
(before coil the drop is ~0)

IMD:
Mine has ~0.0013% at full power, Leach is about 0.0059% at
similar powerlevels. (But into 8 ohm)

THD:
The Leach has an increase of factor ~48 over the bandwidth up to
20khz, this seems pretty much to me ?
Mine has about factor 7. (okay, mine is high OL-gain)
(at 1khz full power mine has ~0.0003%)

Now, i am not sure how representive this is, as the Leach values
are from realworld measurements, but i think that my small circuit
still has a lot of potential...

Mike (now some kind of proud...)