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Old 29th August 2012, 01:11 AM   #27051
morinix is offline morinix  United States
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John, Stupid question. What are the complimentary JFETs doing in the feedback of the opamp from here? http://www.diyaudio.com/forums/analo...ml#post3068026
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Old 29th August 2012, 01:58 AM   #27052
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They are a complementary follower in the feedback loop, configured like a filter.
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Old 29th August 2012, 02:22 AM   #27053
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Quote:
Originally Posted by john curl View Post
At 32, I thought that I had a 'notch' at 19K. John Meyer and I, however, found that my tweeter had a 'notch' at 19K. You never know.
When I worked as a lead engineer of support and development of railway radio and electronics, one engineer had been waked up in the middle of the night and sent to a remote station to repair an equipment. They said, the dispatcher had a crappy voice, so he took spare microphone and microphone preamp, and left the town in the rear cabin of a cargo train. When he returned back he was very angry, because indeed the dispatcher has scratchy voice. He had also a scarf around his neck, and was drinking hot tea with honey and raspberry, to heal his throat...
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Old 29th August 2012, 03:26 AM   #27054
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Originally Posted by john curl View Post
What useful information is lost through all the 'romp and stomp' that plagues this thread, is why I, at least, strive to keep it going, even though I have to repeat myself.

impart what seems to 'work' in making a successful audio product, and it is certainly more than just an interesting circuit topology.
An observation from the cheap seats is that quite a few interesting posting/observations/statements are quite quickly glossed over and surplanted with detailed discussions of sub 100db artifacts or measurements germain to the optical spectrum... (that's a joke son) .

John asked about quality audio pursuits to no real response a few weeks or more ago, although I trully believe that a large number of the people that struggle through the noise to examine this thread are really in pursuit of. I know that I was.

John Curl's reputation and career have been closely aligned with the pursuit of high performance, quality audio design for many years. To follow a thread based on his statement design and find a hostile environment bent on disproving it's fundamental ability to be cutting edge, sonically, must be quite confusing to the poor soul looking for enlightenment wading through the endless pages presented here.

Richard Marsh has been asking fundamental questions based on the reality that audio quality in the real world sucks, how can we move forward, similar followup... Oh well.

The whole point in my speaking out is that I have noted a few very interesting postings that deserved more attention, and doing so would possibly yield insite for all, that were glossed over and not examined with an open mind and egos in check.

I'll point back to Frank's (FAS42) postings and the follow up by Jan concerning (was it AC/DC) compressed recording (bad) and Franks addition of it to his must listen list as an example (good)... This when thought about, and from my experience, opens up an interesting avenue of discourse of the type worthy of this thread and it's namesake.

I don't have the bandwidth right now to put much time into this but think about how a very complex piece of music would appear in the compression discussion. And then think about what is involved in a piece of electronics that would allow it to keep all of the aspects of that recording sorted out, pure and clean sounding without the more dynamic aspects of the music stepping on the more subtle details... The signal still looks compressed in Jan's snapshots, but one system might allow you to hear a pin drop clearly with all hell breaking loose around it while another would turn it into sonic mush. Which measurement would point this out?

Mike
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Old 29th August 2012, 06:17 AM   #27055
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Quote:
Originally Posted by MikeBettinger View Post
John asked about quality audio pursuits to no real response a few weeks or more ago, although I trully believe that a large number of the people that struggle through the noise to examine this thread are really in pursuit of. I know that I was.

...

I don't have the bandwidth right now to put much time into this but think about how a very complex piece of music would appear in the compression discussion. And then think about what is involved in a piece of electronics that would allow it to keep all of the aspects of that recording sorted out, pure and clean sounding without the more dynamic aspects of the music stepping on the more subtle details... The signal still looks compressed in Jan's snapshots, but one system might allow you to hear a pin drop clearly with all hell breaking loose around it while another would turn it into sonic mush. Which measurement would point this out?
I appreciate your thoughtful comments, Mike. It has been a struggle to firstly get a system to work that well, and secondly to make people aware that this is a very realistic goal. My experiences have been that no matter how complex a piece of music, or sound making, that a setup refined up to the highest level will allow that level of unravelling to take place, in the ear/brain of the listener.

The key, and therefore the answer to your last question, from my point of view, is that low level, high in the audio spectrum frequency, distortion has to be minimised. Especially when the system is running at high average power levels. As an example, to test the capability of an unknown system I would use that AC/DC track, winding up the volume steadily and focusing on and listening to the image, the tonality of the cymbals only, nothing else, as the sound level increased. That would tell me almost everything significant about the system that I would need to know, to assess it ...

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Old 29th August 2012, 08:03 AM   #27056
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Quote:
Originally Posted by MikeBettinger View Post
An observation from the cheap seats is that quite a few interesting posting/observations/statements are quite quickly glossed over and surplanted with detailed discussions of sub 100db artifacts or measurements germain to the optical spectrum... (that's a joke son) .

John asked about quality audio pursuits to no real response a few weeks or more ago, although I trully believe that a large number of the people that struggle through the noise to examine this thread are really in pursuit of. I know that I was.

John Curl's reputation and career have been closely aligned with the pursuit of high performance, quality audio design for many years. To follow a thread based on his statement design and find a hostile environment bent on disproving it's fundamental ability to be cutting edge, sonically, must be quite confusing to the poor soul looking for enlightenment wading through the endless pages presented here.

Richard Marsh has been asking fundamental questions based on the reality that audio quality in the real world sucks, how can we move forward, similar followup... Oh well.

The whole point in my speaking out is that I have noted a few very interesting postings that deserved more attention, and doing so would possibly yield insite for all, that were glossed over and not examined with an open mind and egos in check. Mike
Thx -- Two thumbs up to you -- sometimes it seems like the response is the equivalent of a blank stare and then moves to a completely different subject.

Last edited by RNMarsh; 29th August 2012 at 08:05 AM.
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Old 29th August 2012, 08:08 AM   #27057
RNMarsh is offline RNMarsh  United States
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Originally Posted by john curl View Post
They are a complementary follower in the feedback loop, configured like a filter.
Buffers the high input c to reduce distortion.
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Old 29th August 2012, 08:11 AM   #27058
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Agree Frank. And would add that power supply break-through (or Power Supply Rejection Ratio for us engineers ) would also play a large role.
But I would think that a regular S/N measurement, which gives us dynamic range, would capture that.
Don't forget that a THD+N measurement not only captures the distortion but also the noise floor (which includes power supply mush as well).
Some sophisticated audio measurement equipment (some dedicated like AP, some PC-based like Spectrum) can test equipment with a multifrequency signal (there is even an ISO standard test signal with 31 different frequencies, mimicking music). Under those circumstances you can see the minimum signal that can be reproduced.

A weak signal in the presence of a large signal will be clearly audible if it is above the noise floor, I would think.
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jan
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Old 29th August 2012, 08:34 AM   #27059
fas42 is offline fas42  Australia
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Quote:
Originally Posted by janneman View Post
A weak signal in the presence of a large signal will be clearly audible if it is above the noise floor, I would think.
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jan
How about testing with a mix of a constant amplitude low level, higher frequency and a much higher, variable level, low frequency and seeing how the modulation artifacts vary especially in regard to the high frequency component as the power supply is more and more stressed?

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Old 29th August 2012, 08:41 AM   #27060
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by janneman View Post
Agree Frank. And would add that power supply break-through (or Power Supply Rejection Ratio for us engineers ) would also play a large role.
A weak signal in the presence of a large signal will be clearly audible if it is above the noise floor, I would think.
Comments?

jan
General rule for DIY'ers: A poor psrr amp can be offset by a really good, low noise, low z regulated power supply. The worse the power supply, the greater the amp needs a higher psrr. Usually with small signals the regulated power supply is common. But in power amps, for example, it isnt as common (rare?) to have low noise, regulated voltage and the need for higher psrr is more important.
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