Abomination! or Painting a Mustache on the Mona Lisa meets the Island of Dr. Moreau - Page 10 - diyAudio
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Old 16th December 2008, 07:32 AM   #91
roender is offline roender  Romania
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Quote:
Originally posted by lineup

AD797 second stage idea.
The idea is to use a floating mirror - gives at all output voltages same Vce across Q8 and Q9.
Lineup regards

Well, the idea behind floating CM is to present the same higher impedance on both sides of the LTP outputs, hence a very well balanced first stage at all working frequencies, hence a very high OLG, but unfortunately, only at LF.
The Achilles heel of this topology is VAS output impedance, which is high. Any attempt to load the VAS will ruin OLG.
It actually works really well only coupled with a very well designed output stage.
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Old 16th December 2008, 10:39 AM   #92
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Quote:
Originally posted by ostripper

It was the 1381/3503's ,these devices EXCEL in normal
operation.. but when they saturate, they really stick hard.
So , I resimmed mje 340/350's.. bang, fixed the problem.
I had similar problem with these same and some others models - from fairchild site
especially ...
I use LTSpice.
I was done small modifications in models:
*+ QCO =0.05
*+ RCO =50.1187
- comment these parameters or set to zero.

And small quote from KSC3503.lib:
* If QCO and RCO are set to zero, this model applies to
* the Gummel-Poon model LEVEL 1.

LEVEL=2 parameter is unrecognized by LTSpice anyway, so it seems You can sfely
comment it out, then all works fine.
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Old 16th December 2008, 02:34 PM   #93
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Quote:
Originally posted by lineup


MJL21193.
As your nice amplifier is close to AD797 input and 2nd stage
you may some time when you wish,
try to use the AD797 second stage idea.
Hi lineup,
I try to avoid complications if the results are not going to realize a substantial improvement. One area in this topology that I'm trying to avoid changing is the VAS. I don't want to upset the stability of this design - it is the biggest attraction.

Quote:
Originally posted by roender

It actually works really well only coupled with a very well designed output stage.

Thanks for the explanation roender,
What do you think of my latest schematic? I think I have the bugs worked out and I've taken it to it's limit in simulation. I need to build it to try out the changes that I've made and compare to the performance of the Abomination.
Can you see any glaring mistakes?
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Old 16th December 2008, 02:41 PM   #94
lineup is offline lineup  Sweden
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Quote:
Originally posted by MJL21193
Hi lineup,
I try to avoid complications if the results are not going to realize a substantial improvement.
MJL21193
Maybe you did not notice, but I said:
... maybe some time if when you wish

Meaning, put it into your knowledge bank and try it out some other time.
Now, I know you have got a new idea from me.
Would I expect a thank you .. maybe.
But I can not require any thanks from anybody, I know
There are so, so many people without any sense of gratitude on our forum.

Lineup
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Old 16th December 2008, 02:49 PM   #95
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Quote:
Originally posted by ostripper

This is what "got me on the run" .. to explore how
your amp and mine handles mild and gross clipping.

The abomination does the best, it has less gain , just asymmmetric as noted above (just a little sticking)..livable .Mine sucked when overdriven.(both asym. and "sticks"... saturation)
First I thought it was the design..nope
It was the 1381/3503's ,these devices EXCEL in normal
operation.. OS
Sorry OS, but that is not the case. I swapped the 2SA1381/SC3503 for the MJE340/350 in my version of the Frugal II and the clipping is actually worse.
Keep in mind that I reduced VAS current to ~2.2mA per leg to help the clipping instability problem before.

I have solved the gross clipping performance of this latest amp by going back to the LED as opposed the the rather ridiculous way I had it configured when roender commented on it. I expect the simulated clipping performance to match the real work amp - as seen earlier a shot of the Abomination clipping 5Vpp over input sensitivity.


Quote:
Originally posted by wojtek5001


I had similar problem with these same and some others models - from fairchild site
especially ...
I use LTSpice.
I was done small modifications in models:
*+ QCO =0.05
*+ RCO =50.1187
Hi wojtek5001,
I use Multisim and I don't have any problem with the 1381/3503 models from Fairchild. They seem to be very good.
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Old 16th December 2008, 02:51 PM   #96
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Quote:
Originally posted by lineup


MJL21193
Maybe you did not notice, but I said:
... maybe some time if when you wish

Sorry lineup,
Thanks for pointing it out and I will put it in my bag of tricks. I didn't mean to sound ungrateful.
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Old 16th December 2008, 03:06 PM   #97
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Quote:
Originally posted by MJL21193

I use Multisim and I don't have any problem with the 1381/3503 models from Fairchild. They seem to be very good.
I was talking just about problem that (as I think) Ostripper experienced, as hi said "sticky clipping" or something like that. I don't tell that these models are bad - they're
probably good, but just behaves strangely when used in VAS and amp is driven to clipping.
And that was tested only with LTSpice - on other software I have no idea.

To Ostripper: can You try my mods and tell if that helps?

Edit:
hi sad: "but when they saturate, they really stick hard"
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Old 16th December 2008, 03:52 PM   #98
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Quote:
Originally posted by wojtek5001


I was talking just about problem that (as I think) Ostripper experienced, as hi said "sticky clipping" or something like that.

Hi,
That's what happens in the real amp though. I posted a pic over at the Frugal thread and there is one here of the Abomination amp clipping. The sticking is plainly visible.
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Old 16th December 2008, 04:17 PM   #99
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I just talking about problem that (as I think) Ostripper experienced,
during __simulations__. I had no idea what happens to Your amp in reality.
I assume (maybe I'am wrong), that ostripper tooks about sims only
(He says that he "resimmed" with another model - so ...).
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Old 16th December 2008, 04:30 PM   #100
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O.K. I was look at Your picture with that "sticky clipping",
and must admit, that it looks very similar to my sims.
But in sims that happens regardless of frequency.
Even at 100Hz something "stick" for about 2ms
(I'll try to post some pictures tomorrow).

That sticking dissappears when i correct model as in my first post.
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