John Curl's Blowtorch preamplifier part II - Page 3394 - diyAudio
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Old 31st January 2013, 09:28 PM   #33931
Bonsai is offline Bonsai  Taiwan
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Quote:
Originally Posted by AudioLapDance View Post
PMA dabbles in all things, not sure why you're trying to 'nail' him to one technology? He was just playing with a JLH 10W amp (about as simple and discrete as you can get!) and before that did lots of revisions of a great discrete preamp. But before that he was playing with a OPA627/BUF634 linedriver/headamp ...



Hey PMA, can you be more specific about your more appropriate layout this time around and what this "buffer" is (discrete or chip)?



Cheers,
Jeff
Not trying to 'nail' anyone. Just an observation . . .
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Old 31st January 2013, 09:30 PM   #33932
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Originally Posted by Steve Eddy View Post
Yeah, Deane (I'm not misspelling his name by the way) did promote a flat group delay, or what he termed "Deviation from Linear Phase" or DLP for short. He wrote about it in a 1986 paper he presented at the 81st AES Convention, titled High Frequency Phase Response Specifications: Useful of Misleading?

But as far as I'm aware, he just started out with very well engineered transformers and applied external RC networks to achieve the high frequency response he was looking for.
With the capability to measure in everyones hands - we ought to start measuring this more often in respect to tube pre/amps (transformers) as well as termination of speaker cable lines at a given loudspeaker and the like... Microphones, too. Sware and HWare that run by PC can do this easily now.
How does terminating a cable at the speaker terminals improve Group delay? What would it take? Thx-RNMarsh
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Old 31st January 2013, 09:39 PM   #33933
RNMarsh is offline RNMarsh  United States
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Originally Posted by gpapag View Post
Thank you Richard

The second attachment is from this article:
http://www.keith-snook.info/Wireless...%20Sandman.pdf

The first attachment reminded me of this:
http://www.ti.com/lit/an/sboa031/sboa031.pdf
Although is a totally different circuit and has nothing to do with Richard’s distortion reduction one, I post the link due to the discussion of output buffering
(I have built the circuit with LF353N that I had available . It drives my 600 Ohm AKG K240 headphones).

Regarding distortion reduction on bridge circuits, there is one EE participant here who has done a lot of work on this. But he always keeps a low profile

George
Boy you are good! That was fast, too. yes, Sandman in Wireless World discloses this error-take off approach and gives some back ground to Black (Mr neg feedback). It is Sandmans own original idea. Wireless World 1974.

I think it has great potential. Maybe with power amps? They still need a lot of help. Or low thd oscillators... the concept can be used somewhere to advantage. It seems to have been under-developed.... Is this what Walker/Quad amps were inspired by? Thx-RNMarsh

Last edited by RNMarsh; 31st January 2013 at 09:51 PM.
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Old 31st January 2013, 09:49 PM   #33934
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Originally Posted by Bonsai View Post
Here's how I do it. No heavy currents involved.

Augmented Feedback Error Correction (AFEC)
I think that's called Hawksford error correction, but there's *always* priors in electronics. Usually Blumlein or Baxandall!

Thanks,
Chris
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Old 31st January 2013, 09:55 PM   #33935
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Originally Posted by Chris Hornbeck View Post
I think that's called Hawksford error correction, but there's *always* priors in electronics. Usually Blumlein or Baxandall!

Thanks,
Chris
No, that is a comparitor between I/O, etc. Sandman shows something different in functionality. Inverting the error signal and feeding it into the output (inverted) to cancel thd. Thx-RNMarsh

Last edited by RNMarsh; 31st January 2013 at 09:58 PM.
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Old 31st January 2013, 10:00 PM   #33936
Bonsai is offline Bonsai  Taiwan
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Chris, Richard is right. It is not Hawksford.

Yes there are priors, which AKSA highlighted after I originally posted it up a few months ago. However, as far as I can tell, it's never hit the mainstream.
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Old 31st January 2013, 10:05 PM   #33937
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My comment wasn't about the Sandman; it was about "This approach measures the difference between the input (the reference) and the main amplifier output which also includes the error signal. The output of the measuring amplifier represents the error difference and is applied to the main amplifier feedback node as an error correction signal." No biggie either which way.

Thanks,
Chris

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Old 31st January 2013, 10:17 PM   #33938
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I understand. However, we here have a collective capability to make things happen.
There are guys involved in SIM who are wizards at it but just rehash the usual topology until it is a Taj Mahal. Bonsai -- we just need to keep pushing and show it to people until it gathers enough head of steam. Maybe others want some one else to start and show the way then they will take it and run with it. Even though John's forum isnt the right place... I am getting it exposed to as many people as possible to explore it further. I thought of something like this in concept only as a means to lower my oscillator thd on another forum. Then I rediscovered Sandman's invention. Thx-RNM

Last edited by RNMarsh; 31st January 2013 at 10:22 PM.
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Old 31st January 2013, 10:21 PM   #33939
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Originally Posted by RNMarsh View Post
They still need a lot of help. Or low thd oscillators... the concept can be used somewhere to advantage. It seems to have been under-developed....
I had played a lot with error correction since the 70s. Everything playing with feedback is too acrobatic, on my opinion, as it deal with comparisons ( phase problems due to delays). The method used with some low HD OPAs (including Scott's baby) seems more healthy: Low open loop distortion, huge gain, huge feedback.
Error cancellation (not the same thing) looks more promising, but need good paired parts, so not industrial neither.
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Old 31st January 2013, 10:37 PM   #33940
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Originally Posted by RNMarsh View Post
I understand. However, we here have a collective capability to make things happen.
Richard, i tried, in the same spirit to start a collaborative project with my protection circuit (same idea).
It works wonderfull i my own amp since 20years. Can be used to add a correction error to any existing amp too.
An ultimate amp protection circuit ?
Collaboration ? Nada, peanuts, nothing !!!!
Thread is dead and i'm too discouraged to do everything by myself, BOM, printed CI etc.
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Last edited by Esperado; 31st January 2013 at 10:45 PM.
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