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Old 23rd March 2010, 09:31 PM   #3961
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"Keep on Truckin' " Ed Simon, somebody has to do the research in audio, today. I'm with you, completely.
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Old 24th March 2010, 05:40 PM   #3962
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Originally Posted by john curl View Post
"Keep on Truckin' " Ed Simon, somebody has to do the research in audio, today. I'm with you, completely.
Tutorials actually, next maybe global feedback vs local networks. The math would lose most folks. But the principle is not too hard to grasp.

If you have a gain stage that follows Out=A*vin + .1*A*vin*vin and you apply feedback the reduction in distortion is well known. The same for Out=A*vin + .1*A*vin*vin*vin.

But when you use Out=A*vin + .1*A*vin*vin * (A*vin + .1*A*vin*vin*vin), the * sign really changes the feedback math.

Of course global feedback works much better when the equation is more like Out=20*A*vin + 2*A*vin*vin *(.05A*vin + .005*A*vin*vin*vin)

So when you compound gain stages of different gain properties but with both contributing to the overall gain global feedback will produce some extra artifacts, better to use local feedback on each stage, but when one stage dominates the gain structure global may be indistinguishable from local.

Note the assumption the total gain open loop and closed loop is the same for these comparisons.

So let us see who is actually reading this thread!
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Old 24th March 2010, 06:21 PM   #3963
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Well Simon, I am reading it, but I look at feedback in the same way, but in much more detail. We have talked about global feedback here, over the years, but usually we get nowhere. This is because of the FM modulation that is ignored, and even denied by many. It took us many decades, but first it was TIM or essentially slew rate limiting, that was shown to be very important. Of course, when you increased slew rate, all else being equal, you usually increased the open loop bandwidth, open loop linearity, and reduced the total amount of feedback. This all helped. Then, about 30 years ago, FIM or PIM became a topic of interest, but it is still put down by many here.
This weekend, I spoke to my associate who has a new method of measuring FIM. I mentioned him about a year ago, and everyone and his brother jumped on me to reveal his info, even before he gave it to me. Because he is pursuing a patent, he got very upset with me for mentioning it at all, but he tells me that he is moving forward by giving a series of tutorials on this subject at a major university. He, himself, is an engineering graduate of UCB, and has worked at AMPEX, Dolby, Sony, and many other telcom co's in Silicon Valley, and worked for me, when he was a student at UCB in the late '70's. I hope for more in future, but that is all there is, at the moment.
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Old 24th March 2010, 08:26 PM   #3964
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Originally Posted by john curl View Post
This is because of the FM modulation that is ignored, and even denied by many. It took us many decades, but first it was TIM or essentially slew rate limiting, that was shown to be very important. Of course, when you increased slew rate, all else being equal, you usually increased the open loop bandwidth, open loop linearity, and reduced the total amount of feedback. This all helped. Then, about 30 years ago, FIM or PIM became a topic of interest, but it is still put down by many here.
This weekend, I spoke to my associate who has a new method of measuring FIM.

John,

I was just talking about the distortion caused by nonlinearity in the transfer function and how you compound the errors when there are two about equal in gain but different transfer functions cascaded.

The issues such as slew rate limiting, stored charge, and others can cause great harm if not addressed, but they are different issues and need to be analyzed singly before they are grouped into an audio "Mystery!"

Demian

I have started running you resistors, The loose small square ones were not impressive. The wire-wound was and your Caddock is better than mine! I missed that one of the small round single was 332K.. can't measure that high. Of course if anyone has an amplifier that can produce 150 volts RMS with distortion below say -120 I would be interested in trying!

Also did you get my email?
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Old 25th March 2010, 06:38 AM   #3965
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Simon:
I got yours and replied. Did you get mine?
The other precision resistors I guess show that precision doesn't mean good. I guess the 332's were ratio'ed for some reason. When buying surplus you find all manner of stuff.
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Old 25th March 2010, 02:54 PM   #3966
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John,

I came upon this circuit from Graham Maynard that provides variable damping and variable resistive load for cartridges.
Probably (surely) not exactly what you want, but it's another view of the issue:

The ACE

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Last edited by jan.didden; 25th March 2010 at 02:55 PM. Reason: sp
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Old 25th March 2010, 03:14 PM   #3967
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Simon:
I got yours and replied. Did you get mine?
The other precision resistors I guess show that precision doesn't mean good. I guess the 332's were ratio'ed for some reason. When buying surplus you find all manner of stuff.
No Haven't seen a thing
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Old 25th March 2010, 04:11 PM   #3968
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Ed:
Found the note- stuck in the outbox. Its on its way now.
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Old 25th March 2010, 09:44 PM   #3969
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Demian

Here are the results. Note single samples should be 3 db higher.

Jan,

Edited in word and sized in paint.

Note anyone who wishes to repost these as a PDF to this site has my permission

ES
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File Type: doc Demians Samples Artsy.doc (85.5 KB, 47 views)
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Old 25th March 2010, 10:04 PM   #3970
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Here you go.
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File Type: pdf Demians Samples Artsy.pdf (64.5 KB, 101 views)
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