John Curl's Blowtorch preamplifier part II

[john curl]

To further my statement: This is from the 1980 TIM response to Bob Cordell.

[Wavebourn]

Originally Posted by kgrlee

Yup! Anyone going to test Mr. Pass?

KG Sh*t-stirring Lee

I though he is married, no?

[Wavebourn]

Originally Posted by kgrlee

Haven't decided on the new version cos I still can't define the 'perfect' speaker. But why not DSP when your source is gonna be mostly evil digital?

Certainly helps with the best microphone for this millenium

6 is not enough, you either need more, or each 6 motor-controlled.

However, new media is needed, to contain special digital track to control motors.

[kgrlee]

Originally Posted by john curl

There is a progressing difference in tests for op amps. First, might be harmonic distortion, then TIM, then FIM. Each is different from each other, and only partially related. We do NOT do this to sell ideas. We have plenty more to do than that. We do it to IMPROVE audio quality to the best that is possible (once we find out how to do it better)
We have spent man-years with real salary or support to research TIM and now FIM. We do it to learn what is important, AND once WE prove something, everybody else comes up to speed, so to speak. It is the way of things.

Thanks for this John. I'm sure you do. But I was asking about Listening Tests. Didn't even use the rude "Bl*nd" word.

Anyone got John's 'proof' of zillion V/us with MC mistracking? Oops! I see he's posted it. Thanks John.

I've done a bit of work on the subject so am really interested. Gave up after Otala's student cos it was far more comprehensive than my stuff.

[kgrlee]

Originally Posted by john curl

To further my statement: This is from the 1980 TIM response to Bob Cordell.

Thanks for this John. Looks entirely in keeping with the Shure data (which I think you quote) and summarized by the THX chap in Audio. Also consistent with Otala's student. I note you only guess what happens with HF mistracking while he measures it.

While HF mistracking does give probably[*] the highest slew rates with vinyl playback, it is not surprising that you don't get zillion V/us as HF mistracking is a very severe form of Slew Rate limiting.

[*] There IS one other case which is known to give higher slews but I won't complicate the issue.

[Bob Cordell]

Originally Posted by john curl

To further my statement: This is from the 1980 TIM response to Bob Cordell.

Hi John,
Its useful that you put this up. It is one of the more reasonable points you made in that unfortunate fiasco that took place over thirty years ago.

It is always worth noting for perspective that the normalized slew rate for a 20kHz sinewave is 0.125 V/us/Vpeak. My original paper in TIM, called "Another View of TIM" can be found on my website at CordellAudio.com - Home. I believe that the points made in that paper have stood the test of time. Likewise my paper on PIM can be found there as well.

Cheers,
Bob

[Esperado]

Originally Posted by Bob Cordell

My original paper in TIM, called "Another View of TIM" can be found on my website

No need to remind-us about that, sir Cordell. I believe everybody on this forum and every engineer involved in audio have-it in his favorites and your contributions in his library. Your clever and clear contributions as well as your generous and modest way to share your knowledge and experience are universally recognized.
I say clever because all what you had published, or correlate with things we have experienced previously or can be verified by future experiences.
Not the case of all 'so called' gurus.
This words to express our gratitude and pay tribute.

[gpapag]

Originally Posted by kgrlee

[*] There IS one other case which is known to give higher slews but I won't complicate the issue.

FM reception

George

[scott wurcer]

Originally Posted by john curl

Team SY? What team? Dick Sequerra was a close friend to Scott Wurcer for a long time. Dick thinks that Scott is a very good engineer, and that the AD797 is a GREAT product. However, Dick, like me, is suspicious of global loop feedback, so he designed a preamp that did not use global loop feedback, yet used the AD797. Quite a feat!
I just sent Dick a copy of Ron Quan's paper. I hope to get some feedback from him soon, about the paper. You would do well to keep and open mind on this subject, too.

John did you even read the results? There are many modern op-amps that have no PIM by Ron's own measurments. So why distrust global feedback when Ron's tests show no evidence for this at all? Get up to speed no PIM no TIM no FIM, why not address the results?

[kgrlee]

Originally Posted by RNMarsh

can we make a new ambisonic coder/decorder circuit from original schematic? ... with updated circuitry. ??? Something many can then afford to make and use. It's the best thing we have and it was too expensive in original form.

Who has/ where is the schematic to post here?

Mr. Marsh, there used to be a website with schematics of practically all hardware decoders but this died with Geocities.

I can only find http://decoy.iki.fi/dsound/ambisonic...0WW%201977.pdf This is a very old design but in fact ALL hardware decoders followed this topology as they were done by Dr. Geoffrey Barton under guidance from Michael Gerzon. The best in terms of sound quality would be the Minim AD10s.

But today, it is possible to use DSP to get far more accurate decode without passing through a zillion evil OPAs.

VVMic is one such beast. Do you have a good multi-channel soundcard on a convenient computer to play music?

Though VVMic is primarily used to decode Ambisonic B-format into stereo, it is also a surround decoder and can decode to 4, 6, 5.1, zillion.1

Simple 4.0 decode works well on most 5.1 systems.

An Ambisonic B-format recording doesn't record what should come out of the speakers. It records 'what you should hear'. The decoder turns this into speaker signals which, when they reach your ears, recreate the best approximation to what was happening at the microphone. To do this, you need to tell the decoder where your speakers are.

The problem is that for other than rectangles, regular polygons and other simple shapes, its quite difficult to dream up the correct decode. It's only this century, that the computing power has been available to do the optimisation at home. The BLaH team, Benjamin, Lee and Heller, have presented a series of papers on both Classic Ambi decoders as well as new ones which have arbitrary speaker positions.

But most people will get good results with simple rectangles and/or square decodes on their 5.1 systems.