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Old 8th November 2012, 10:16 AM   #121
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by danielwritesbac View Post
LM3886 and other Overture series contain the Spike system which exacerbates clipping and indeed sounds like a hard clipper to me. This is unkind to outputs and worsens the situation with a slight bit of sticking. Whatever the case may be, just imagine the worst outputs ever. Now, if you enclose this noisy TV power amp chip inside the feedback loop of a small signal op amp (nesting), then the problem is decreased by same proportion of the new global loop. That's automated quality control.
Short answer: Noise reduction (since it is actually predictable, more accurate term is "distortion reduction").

P.S.
The small signal op-amp in this case is run on regs, and the "clean reference" effect is copied to the entire amp via feedback. A similar approach with a discrete amp is to run the input+predrive (or driver chip) on regs or capmulti.
Quote:
Originally Posted by rsavas View Post
Thanks for your explanation, Daniel. You certainly have more experience than I using these parts. Has the posted ckt has been built and tested?
Rav,
you are misguided.
I think that Daniel's explanation is rubbish.
How can Spike be over-ruled by enclosing the chip amp inside the composite?
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Old 8th November 2012, 01:32 PM   #122
bcmbob is offline bcmbob  United States
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Thanks Andrew, that's the picture I was seeking. Anything that comprehensive would, in my limited understanding, remove the result from the MyRef concept. That's perfectly fine if the sound produced is high quality, and I for one would love to participate in formalizing an LME498xx based amp with the features promoted by Daniel. Hope it develops.
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Old 8th November 2012, 02:57 PM   #123
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Quote:
Originally Posted by AndrewT View Post
Rav, you are misguided. I think that Daniel's explanation is rubbish. How can Spike be over-ruled by enclosing the chip amp inside the composite?
Any error at the speaker output is reduced by same proportion as the added global negative feedback loop that goes back to the small signal amp. Otherwise, the nesting concept would be completely useless.
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Old 8th November 2012, 03:06 PM   #124
rsavas is offline rsavas  Canada
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I reason that, if the signal goes non-linear, by a large margin, i.e. clipping, no amount of NFB can make a correction for this. Just seems logical, doesn't it?
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Old 8th November 2012, 03:15 PM   #125
AndrewT is offline AndrewT  Scotland
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Daniel was complaining that Spike protection is the 3886 problem.
Daniel went on to try to say that enclosing the 3886 inside the Howland and inside the composite that the combined arrangement reduced or eliminated the undesirable effects of Spike protection.
That's what I read and understood from post115.
Have I got it wrong, or is Daniel back on Venus?
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Old 8th November 2012, 07:58 PM   #126
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Quote:
Originally Posted by rsavas View Post
I reason that, if the signal goes non-linear, by a large margin, i.e. clipping, no amount of NFB can make a correction for this. Just seems logical, doesn't it?
That's true (in proportion to the gain).
With nesting, errors at the output are merely reduced, not eliminated.
But, any port in a storm, right?

P.S.
I'm not offering nesting as an excuse to put a huge amount of effort into a TV chip that contains a hard limiter. Personally, I'd rather have an LME chip (driver chip), or one of ST's with the softie limiter. But, then I wonder if when using one of ST's chips if I'd like to have the quality control assistance of nesting? And I'd just have to answer Yes.
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Last edited by danielwritesbac; 8th November 2012 at 08:06 PM.
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Old 8th November 2012, 08:20 PM   #127
rsavas is offline rsavas  Canada
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Quote:
But, any port in a storm, right?
Okay, you lost me on this expression, I have heard "storm in a tea cup", but this one is new to me = lost
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Old 8th November 2012, 08:31 PM   #128
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Any port in a storm is just like the Fix-A-Flat product that makes the flat tire round and puts in some glue. That's not the final answer, but it was much better than a flat. In context, I said that nesting basic quality active parts is an improvement, but not a substitute for high quality active parts. That resolves: Nested LM3886 is not a substitute for LME driver chip.
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Last edited by danielwritesbac; 8th November 2012 at 08:37 PM.
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Old 8th November 2012, 08:45 PM   #129
rsavas is offline rsavas  Canada
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Fix-A-Flat stuff, oh ya we call it Elephant snot. Yes, I agree LME drivers are nice parts, so back to working on my LM49830/LatFet design, any advise for me on this?
LME49830+LatFET, yet another for design review
Thx Rick
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Old 8th November 2012, 09:34 PM   #130
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Actually yes. Your design requires a DC servo.

The wrong NFB cap value is shown and that will make for loud mids with boomy bass sound. However, the right value is so large (1000u~2200u) that it would "Taser" damage the input (or cause bouncing offset if you tried bypass diodes). Impasse. That design has no correct value of NFB cap. Therefore it needs a DC servo.

Operating voltage at 100v+100v (???), but gain of 28, means there's no source device for it--I think you need to include a preamp run on discrete regulators. The design shown has enough power; however, I doubt you can find enough speaker. Perhaps a bit lower voltage to reduce extra costs at heatsink and transformer?

And, if you should happen to get a forwards sound for that power amp, you can copypasta this from my TDA7294 power circuit: "Pair 220u amplifier board power caps and a single 2u polyester rail to rail." I'm just saying that while you're paying shipping for those 100u, you might also want to purchase some 220u to have the option available.
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Last edited by danielwritesbac; 8th November 2012 at 09:51 PM.
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