Bob Cordell Interview: Error Correction - diyAudio
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Old 25th October 2006, 06:06 PM   #1
mikeks is offline mikeks  United Kingdom
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Post Bob Cordell Interview:

Here & presentation here.
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Old 25th October 2006, 07:31 PM   #2
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Nice interview. As ever, Bob succeeds to get his points across coolly and convincingly (if you know just enough engineering).

Ahh, those TIM wars in the 70-ies! Cordell vs Otala/Curl etc....

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Old 25th October 2006, 08:02 PM   #3
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I like it.
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Old 25th October 2006, 09:06 PM   #4
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Default I agree.

Excellent interview. Very grounded in reality and science with subtle pokes at the psychology of subjectivism.

Thanks for the posting.
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Old 26th October 2006, 03:43 AM   #5
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I had a chance to meet Bob last weekend at the Rocky Mountain Audio Fest in Denver. They had an amplifier design Q&A, so I was able to pick his brain about his error correction amplifier AES journal article. He is a nice guy. He has a web site here You can download his papers there.

One interesting thing I learned from the discussion. In his amplifier, you'll see series R-C networks from the power MOSFET gates to ground. These networks allow a smaller gate resistor while still preventing RF oscillations in the MOSFETs (400 MHz!). He gets away with 47 Ohms, giving a larger bandwidth than what you get with the more typical 200 Ohms or so. The series R-C doesn't seem to impact the bandwidth at all. But it does terminate the gate with a resistance at RF frequencies.

22 years after the publication of the article, and he is still a fan of error correction. The amps in his active speaker don't use error correction though. I think this was in the interest of simplicity and being able to have them be small enough to cram into a pretty small speaker enclosure.
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Old 26th October 2006, 07:06 AM   #6
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I just had a look at Bob's AES paper. Mosfets on the output, distortion around .005% at 20KHz. Has Doug Self read this?
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Old 27th October 2006, 04:03 AM   #7
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In one of the PDF's in Bob's site, there is an amp. The amp is attached below.
The output stage looks like triple darlington, Q5+Q6, Q7+Q8, Q9+Q10.

Why is that Q5+Q6 and Q9+Q10 's emitors are attached to the output node, while Q7+Q8 are not attached to output? What is the reason to make Q7+Q8 have different connection than Q5+Q6 and Q9+Q10?
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Old 27th October 2006, 12:50 PM   #8
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by lumanauw
Bob's site..
Where?
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Old 27th October 2006, 01:24 PM   #9
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Just checking the pp file from Mr. Cordell. It seems that I have invented a "super gainclone" Didn't know the name was "super". I named it "high performance"....

Interesting to see that a such a famous person wants to even mention the LM3886
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Old 27th October 2006, 01:45 PM   #10
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Quote:
Originally posted by peranders
Just checking the pp file from Mr. Cordell. It seems that I have invented a "super gainclone" Didn't know the name was "super". I named it "high performance"....

Interesting to see that a such a famous person wants to even mention the LM3886

Wow! YOU invented the gainclone? Or just the name? This is an interesting question. If you clone something (as in 'rip off') can you then claim to have it invented? This puts a whole new light on the term 'intellectual property' (on both of the words).

Jeez....

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