Are we at stage 2 now?
No stage 3, but of course it was around the proverbial 40yr ago (and longer).
http://www.analog.com/media/en/tech...018494695982855668424783486554001060AN348.pdf
I think a search of the literature will find that this was well known a long time ago.
Gee
Whenever I show that I get flack. Do you have a cite that perhaps mentions the proper mounting of capacitors?
And what about the uproar over DA?
Maybe that longer feedback path is important in cases of RF applications , for AF application it is not so important ,
doing series connection for those`super critical ` resistors increase reliability of unit , amp , preamp ,smps ,.... .
which is more important .
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Radio Amateur's Handbook. I have the '67 edition from when I was studying for my ticket.
BTW -- In Damir's CFA PA that I heard and tested, it too used many resistors in series for his fb resistor. And, his pcb layout keep the path short. One thing that could be done is to replace that resistor with a single one and relisten. I am still curious as to why the CFA - and Damir's in particualr) - performs so well. I dont have that amp any more but maybe later can do that for intellectual curiosity.
It could also just be a hundred such details combined for the best end-result. I think this is a point JC has been saying for a long time.
THx-RNMarsh
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I didn`t know that Damir have used series connected Fb resistors , it`s wise decision any way , amps reliability wise on the first place .
Why Damir CFA amp perform&sound so good ? ,
-it is because Damir is excellent apm designer for sure.
-Generally speaking long time ago Mr.Bruce De Palma have basically defined whats wrong with VFA topology and why CFA is better solution for AF , without to mention VFA or CFA term in his audio related article .
- IMHO one of very important amp design detail is to care about interaction between PCB conducting traces having in mind basic Lenz law , special in case when AB class OPS is used .
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Why only series resistors?
I often use resistors in parallel iside the NFB loop, using 1W resistors. I don't have to, I just like to. Using for example two 16.5k reistsor to obtain 8.25K.
I am aware that series resistors are sometimes used in commercial devices for reasons of logistics, it's simply cheaper for a manufacturer to use several cheaper and more common types they use anyway rather than a single value piece in just one spot. H/K does this on occasion, for example in their 820 power amp.
I often use resistors in parallel iside the NFB loop, using 1W resistors. I don't have to, I just like to. Using for example two 16.5k reistsor to obtain 8.25K.
I am aware that series resistors are sometimes used in commercial devices for reasons of logistics, it's simply cheaper for a manufacturer to use several cheaper and more common types they use anyway rather than a single value piece in just one spot. H/K does this on occasion, for example in their 820 power amp.
A pillar of sanity, the logic here escapes me.
My take away is one N machine can run 5, which leads to "5 raised literally to the power of infinity".
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I am thankful to Ed Simon and Bruce Hofer for giving me more direction in which to point my Stanford Research SR-1. I got really bored with just static 1-10KHz THD measurements. Now, I might be able to locate a couple of problematic resistor distortions that I never could figure out before. I just used my ears, and had to scrap them from quality audio applications. Some of the most expensive, accurate and pretty ones, too!
See, the fact that Doug Grant and I tried to pass on what some of our module designers learned 35yr. ago isn't even worth a mention, wrong posse.
BTW the SR-1 has 37 AD797's in it.
Mr.Wurcer
I`m not here to defend that N-machine designed by Mr.De Palma , maybe that machine work ,if work than OK ,but if don`t work it`s OK again , I don`t care anyway,
but what bother me in that old story is one tiny fact that N-machine is based on Mr.Faraday rotating disk paradox , where even Mr.Faraday as inventor failed to 100% explain how that thing work.
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It took Lorentz to explain it. There is nothing there that gives more out than put in. What is it with the Mr.?
it seems odd to worry on a Audio related site that some investigator noted effects they couldn't explain
logically its certainly a stretch to reason forward from such a factoid - but does seem popular here
logically its certainly a stretch to reason forward from such a factoid - but does seem popular here
That is where the AD897 is most useful: test equipment. I put them in the front end of my ST1700 decades ago. Work real well with sine waves or even IM. In fact, just about any continuous measurement. Sound OK for audio too, but I think the output stage is biased too lean without added buffering. Too expensive, however, for what they actually are. I will stick to discrete for my best sounding stuff, thank you.
It appeals to those who think "we don't know everything" is the same statement as "we know nothing". A common variant of this is "I don't understand it, therefore nobody understands it". Another one is "you can't prove to me that X is false; therefore X must be true".jcx said:
So the corollary is that as Michael Faraday could not fully explain something electromagnetic it is surely true that all snake oil claims are valid and those who disagree are ignorant like Faraday was. This of course generally comes from people who don't know enough electromagnetics to recognise the mysteries in it, as they don't understand the non-mysteries either.
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