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Old 10th August 2010, 09:31 PM   #281
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I have never tried any other simulator. Look at these messages in the yahoo group:

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There is some flak going around about this "crappy free simulator" by highly skeptical people... It looks to me like people already are skeptical when they try it, and when it fails because of their misuse, that is enough to confirm their skepticism. I say: learn to use it right!!! (isn't this sort of like video game console wars?)

Many models out there are just CRAP. They don't model the actual device at all, often they are a copy of another, sometimes unrelated model, or they are just full of nonsense values. The AC parameters are usually not bad but the DC ones are off the wall. Some models will even make SPICE crash. I really don't get how manufacturers get away with the models, but they do. Fairchild ones are not as bad I've found.

Also, the models included by default with LTSpice are copies from other model libraries. I'm guessing they are included because the developers didn't find anything wrong with them.

I got the CCS to work for the VAS but when adding for the LTP, LTSpice has a total cow. It just won't converge. Screwed with the convergence settings and everything... So I'll give you this file with just the VAS replaced and working right.

I also added ESR to the filtering caps, to make PSRR realistic. Distortion has come to .002%, unless I screwed some adjustment up...

- keantoken
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Old 10th August 2010, 10:09 PM   #282
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Quote:
Originally Posted by keantoken View Post
I have never tried any other simulator. Look at these messages in the yahoo group:

Yahoo! Groups

There is some flak going around about this "crappy free simulator" by highly skeptical people... It looks to me like people already are skeptical when they try it, and when it fails because of their misuse, that is enough to confirm their skepticism. I say: learn to use it right!!! (isn't this sort of like video game console wars?)

Many models out there are just CRAP. They don't model the actual device at all, often they are a copy of another, sometimes unrelated model, or they are just full of nonsense values. The AC parameters are usually not bad but the DC ones are off the wall. Some models will even make SPICE crash. I really don't get how manufacturers get away with the models, but they do. Fairchild ones are not as bad I've found.

Also, the models included by default with LTSpice are copies from other model libraries. I'm guessing they are included because the developers didn't find anything wrong with them.

I got the CCS to work for the VAS but when adding for the LTP, LTSpice has a total cow. It just won't converge. Screwed with the convergence settings and everything... So I'll give you this file with just the VAS replaced and working right.

I also added ESR to the filtering caps, to make PSRR realistic. Distortion has come to .002%, unless I screwed some adjustment up...

- keantoken
Yes , you do have to know SOMETHING to make the best use of LT. Multisim is like a video game , all GUI and presets .. just your typical "Walmart simulator". I will try your sim and ""ferret" out any new tricks within. You are at present , in my opinion , the best "simulation jockey" on the site at the moment. This title was previously held by Andy C. , whom I thank for MY introduction to LT.

Using LT , then having the real thing to play with proves beyond a doubt that simulations are not "lies", as they are VERY close to real world operation.

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Old 10th August 2010, 10:18 PM   #283
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Okay, replace C6 with 5pF instead of 22p, and C7 with 680pF. Then make sure the line reads ".param dlycyc=1", I turned this off to find the oscillation. C7 prevents the CCS from oscillating.

Now THD reads less, at .0005%. I forgot I made those changes.

I would comment more, but don't have time at the moment.

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Old 10th August 2010, 10:54 PM   #284
wahab is offline wahab  Algeria
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A fourier analysis...
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Old 11th August 2010, 02:42 AM   #285
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I was never able to honestly compare, here is a file for full simulation of both versions. I was in a hurry before. Yes, there is barely a difference in distortion for this position. I think in the LTP the CCS would work better.

Some say a precisely matched LTP improves sonics audibly, and if this is true I wonder what effect the voodoo CCS will have.

I wasn't able to simulate the CCS for the LTP because the simulator won't converge (not soon at least)... It evidently has problems with this type of CCS. So I don't know how much gain there is by putting it there.

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Old 11th August 2010, 03:43 AM   #286
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Ah , you got it... keen. 6- 1 millionths of a mA , WOW. Must be voodoo.

a ??? R21,22,20 custom values. Are these needed to make this thing stable ? By that huge 560pF cap at the base of Q13, it appears that there is a stability issue ??? And wahib's fourier shows very little improvement in performance. Hmmmm.
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Old 11th August 2010, 06:52 AM   #287
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I wouldn't expect it to make any difference in the VAS position, but I would try it on the LTP.

The higher R22 and R21, the better performance, because the feedback loop has more to "kick against". I don't know if the bootstrap is necessary, I'll let you be the judge of that - the rail filtering probably works well enough. I chose the resistors to keep at least 1mA quiescent through Q13 and Q12. R22 current subtracts from output current.

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Old 11th August 2010, 10:43 AM   #288
AndrewT is offline AndrewT  Scotland
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Quote:
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Ostripper, when you run that wire, what node should the shield be connected to?
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If you run the shielded wire just tack the ground shield to the voltage board ground connection on just 1 end of the wire . I did this on the first "frugalamp" (like the AX) no problems.
consider tapping the shield into the output. Then at the -IN end, the shield is at output voltage and the core is also at output voltage and so is not influenced by any other interference that passes close by.
Connecting the feedback shield to any ground reference just seems wrong. But I'm no expert, on anything.
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Old 11th August 2010, 03:16 PM   #289
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Andrew, if both the core and the shield are connected to Output, would the shield be effective at all? I don't think so. It should be connected to one of the grounds.
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Old 11th August 2010, 03:39 PM   #290
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consider tapping the shield into the output. Then at the -IN end, the shield is at output voltage and the core is also at output voltage and so is not influenced by any other interference that passes close by.
Connecting the feedback shield to any ground reference just seems wrong. But I'm no expert, on anything.
Would that not be the same as a plain single core wire ??? You are very concise , Andrew.. don't sell yourself short. I would not want to have a "shootout" with you in the math classroom.

After further thinking , being of such a low impedance the output/NFB trace should not be affected by the rail current traces or capacitor returns until after it is dropped to a low level after the feedback resistor. This does not happen on this amp until the NFB is behind the VAS (in the realm of small signals).
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