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Old 2nd December 2010, 12:14 AM   #31
Bigun is offline Bigun  Canada
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This is weird. after thinking about the current dumping option I found the 1980 paper by Vanderkooy and sent it to the printer.... awhile later my wife (who's not at all involved in my audio addiction) remarks, did you know your daughter plays with his grand daughter ? I just about fell off my chair !

Well it's a darn good read !
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Old 2nd December 2010, 02:19 AM   #32
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Quote:
Originally Posted by Bigun View Post
This is weird. after thinking about the current dumping option I found the 1980 paper by Vanderkooy and sent it to the printer.... awhile later my wife (who's not at all involved in my audio addiction) remarks, did you know your daughter plays with his grand daughter ? I just about fell off my chair !

Well it's a darn good read !
Can you post a link, please?
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Old 2nd December 2010, 02:30 AM   #33
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I was just going to post the one link but the Google search gets things from different dates.
Results >current dumping 1980 Vanderkooy
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Old 2nd December 2010, 03:04 AM   #34
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Do you mean this one?

http://quad405.com/jaes.pdf
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Old 2nd December 2010, 04:08 AM   #35
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Well I was just searching for what Bigun was referring to but I'm pretty sure that's the one he means. They also published a two part article "Current Dumping: Does it work?" in the June and July 1978 issues of Wireless World.
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Old 2nd December 2010, 06:04 AM   #36
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Quote:
Originally Posted by Hearinspace View Post
Well I was just searching for what Bigun was referring to but I'm pretty sure that's the one he means. They also published a two part article "Current Dumping: Does it work?" in the June and July 1978 issues of Wireless World.
I don't believe it is a coincidence: I made my "Non-Linear-Approximation-Cheating" design approximately at the same time. Akashic field indeed does exist. Paleontologists insist that an axe of the same form was made of different materials simultaneously in different remote locations on the Earth, as well as kitchenware of similar shapes...
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Old 2nd December 2010, 06:30 AM   #37
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Wellllll, the three of you are human after all. It seems natural to me that of tens (or hundreds) of thousands of people who grew up learning electronics (or any other discipline) in a world with a given state of the art, it's not weird that at least several of them would be poking around the same frontier. No?

On the other hand, right this very moment MILLIONS of people are dreaming. Just think of it!
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Old 2nd December 2010, 12:39 PM   #38
Bigun is offline Bigun  Canada
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Originally Posted by Wavebourn View Post
Do you mean this one?

http://quad405.com/jaes.pdf
Yes, this is the one !

It pretty much answers all my questions about this error correction business. Unfortunately, also confirming that you can't escape from using negative feedback at the same time.
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Old 6th December 2010, 12:12 AM   #39
jcx is offline jcx  United States
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Default Black's Feedforward: a sim

I worked up this "current dumping" Black's Feedforward sim from the jaes paper - sized for a headphone load since I'm using a op amp model with ~30mA output current limit

playing with the signal level it appears that it has the annoying property of increasing distortion as output level is reduced - the max % distortion occurs when the output level just starts to use the "dumper" Q for appreciable load current

feedback is necessary to implement the accurate correction amplifier in Black's Feedforward - I don't believe you can easily combine the sim's op amp and unbiased Q to do better in a "pure negative feedback" topology - so the Feedforward idea is valuable if you insist on "Class C+A"

the shown 2 V sine has ~0.01% output distortion, with the distortion growing to ~0.05% at around 200mV drive



it is hard to not comment on Bigun's several swipes at negative feedback:

use enough closed loop gain in a negative feedback amp with only smooth, low order nonlinearities and you get decreasing levels of harmonic distortion with harmonic order - not the 10-20 dB some "no-feedback" types may tepidly apply - it is easy to have >60 dB loop gain at all audio frequencies

there is no other practical way to obtain useful damping ratios - cathode, source, emitter followers are all 100% (local) negative feedback circuits - there are no "inherently low output impedance" amplifying devices

the "no-feedback" crowd's beloved Triode vacuum tube has loads of internal negative feedback - directly causing the observed plate resistance - a tube without internal feedback is a correctly biased Pentode

negative feedback is a foundational principle and should be properly understood and used correctly - ignore audiophool mythology if you want to learn how to design sucessful circuits
Attached Images
File Type: png dumper.png (42.5 KB, 130 views)
Attached Files
File Type: txt dumper.asc.txt (2.7 KB, 5 views)

Last edited by jcx; 6th December 2010 at 12:18 AM.
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Old 6th December 2010, 01:05 AM   #40
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Quote:
Originally Posted by jcx View Post
the "no-feedback" crowd's beloved Triode vacuum tube has loads of internal negative feedback - directly causing the observed plate resistance - a tube without internal feedback is a correctly biased Pentode
Triode don't have non-linearities of higher orders that are essential to devices linearized by negative feedback.

How can you explain that, if it's a pentode with internal negative feedback?

Here is an example of what happens when negative feedback is applied to the device with 10% of distortions of 2'nd order only:
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File Type: png bax_graph_10_percent.png (67.7 KB, 100 views)
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Last edited by Wavebourn; 6th December 2010 at 01:07 AM.
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