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Old 13th June 2012, 01:44 AM   #251
rjm is offline rjm  Japan
Richard Murdey
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@coluke

Thanks for the numerous resources! It's interesting (and impressive) that you worked from "scratch", that is, developed your amplifier circuit from non-audio specific references. I had hoped that there might be line of experience for dealing with these circuits in audio applications, where stability under non-ideal loads, rather than ultra-high bandwidth weighs more heavily on the designer's mind...

(all I found so far was this.)
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Last edited by rjm; 13th June 2012 at 01:46 AM.
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Old 13th June 2012, 03:00 AM   #252
rjm is offline rjm  Japan
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I have this schematic wired in my brain now. Every time I see a CF circuit, I see two diamond buffers with a current mirror strapped between them...

I'll be mowing it into my lawn next.
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Old 13th June 2012, 04:15 AM   #253
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Quote:
Originally Posted by coluke View Post
My starting point were the Sergio Franco's chapter on CF Amplifiers in [I]Analog Circuit Design -
I love Sergio Franco's works I am so indebted...
Thanks for the reminder
-Antonio
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Old 13th June 2012, 04:42 AM   #254
RNMarsh is offline RNMarsh  United States
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The patent on the CFB amp was in 1982 by Comlinear Corp and the first IC version was by Comlinear and Elantec in 1987. Both have written detailed analysis of the circuit. -RNM
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Old 13th June 2012, 08:10 AM   #255
coluke is offline coluke  Italy
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The patent on the CFB amp was in 1982 by Comlinear Corp (...)
You're right - the original one by Nelson & Saller should be US patent 4502020.
L.
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Old 13th June 2012, 08:55 AM   #256
coluke is offline coluke  Italy
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@rjm - as far as I know only Accuphase and Marantz are employing (or have employed) CF topologies in their commercial products, but mainly in preamplifiers. Accuphase's architecture (see the first attachment) is pretty standard (a few old CF opamp by National are based on it), simple and straightforward, and I have indeed verified it works very well using it in a small power wide-BW class AB output buffer for testing purpose (it is capable of almost 20 Vpp into 50 ohm up to 1 MHz with low THD), but if open-loop linearity and gain are of paramount importance then current mirrors in the transimpedance stage are needed - open loop performances of the DB-CM-DB architecture are quite amazing

L.
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Old 13th June 2012, 03:20 PM   #257
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@rjm - as far as I know only Accuphase and Marantz are employing (or have employed) CF topologies in their commercial products, but mainly in preamplifiers.

L.
Since 1990 Accuphase only employ current feedback topologies in their preamps and amps, Marantz is a late comer to the topology. Pioneer, Harmon kardon Sony, Cyrus, Yamaha and a host of others have used the topology, some since since middle 1980s. The most famous and well known was pioneer A400x amp which was applauded for its good sound and cheap price in early 1990s. Also from pioneer youll find the most refined and innovative use of CFB in non feedback and feedback type amps dating from late 80s.

RJM if youre looking for info on CFB National semiconductors (now Texas instruments) papers OA18, OA13 and OA15 is a must have. You need to google for a paper called SmithCFB.pdf too. With these youll know everything there is to know about CFB, the basics that is. The design can then be further refined using wideband techniques and feedforward to improve bandwith slewrate, THD and settling. These refinements are up to you to make though. Start with diamond output buffer seen in your posts.
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Old 13th June 2012, 05:43 PM   #258
sonidos is offline sonidos  United States
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@RNMarsh

Several posts back, you mention still finding the specified jfets at a decent price on the net. But all I could locate were Chinese suppliers offering at that price. So it makes me wonder if the jfets are the real deal on ebay. I am hoping to stick to the parts you specified in the article.

Last edited by sonidos; 13th June 2012 at 05:44 PM. Reason: added note
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Old 13th June 2012, 10:47 PM   #259
RNMarsh is offline RNMarsh  United States
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Default dont know if sources are 'real'

Quote:
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@RNMarsh

Several posts back, you mention still finding the specified jfets at a decent price on the net. But all I could locate were Chinese suppliers offering at that price. So it makes me wonder if the jfets are the real deal on ebay. I am hoping to stick to the parts you specified in the article.
I just looked up jFET's on Internet and bought the lowest priced ones. They were from China and they worked fine. And delivery to my home was very fast. -RNM
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Old 14th June 2012, 02:05 AM   #260
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I thought I had posted this -- 2N5460 is available from Mouser. They have a couple hundred in stock.
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