John Curl's Blowtorch preamplifier part III

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I think it’s clear why Stereophile doesn’t publish yearly in-depth hearing tests for all their review staff. If you are saying you can hear better than everyone else, why not prove it?
Also, with all the measurement data thrown around here it’s pretty strange to see no one has provided any kind of measurement data for their own hearing?
What would that "prove"?
 
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Well from might point of view, and how this all started I was noting that I had no issues with the amplifiers I'm currently boxing up, being basically a composite power opamp has hugely higher loop gain at LF than HF. So 10ppm distortion at 1kHz but only 50ppm at 20kHz. My assertion was that, as no one can hear harmonics of 20kHz is that this is an acceptable compromise.



Now extending it to how much is tolerable at 20kHz is very hard, but as I'm in the 'below 0.1% is good enough for rock and roll' I'm propbably the wrong person to ask.



I should also note that my amplifier choices are driving entirely by space and cost constraints at the moment as I have little of either in my hovel.
 
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Does any of this matter in the home? Probably not. But still interesting to think about.

Imo it would be more surprising if it doesn´t matter. Obviously it depends on a lot of internal realisations, but in a typical audio system at home a nearby interfering source is present, that´s what Jneutron for example means when pointing to "haversine currents" drawn from the mains.
 
People still use Windows?

Stereophile has plenty of dough. They’d just prefer not to flush it down the drain, hence lack of interest in plunking down investment capital.

Who is to say this hasn’t already been done but the results where so embarrassing / crippling that it all went into the shredder?

I take it your background isn’t in sociology or economics?

The term "listening test results" for their reviewers is a bit unspecific but if you meant the usual tests done by audiologists, is there any evidence that better perceptual evalution abilities are mainly caused by differences audiology tests can detect?
 
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I think I will keep posting this image for as long as anyone is willing to discuss it.

I suspect it's about ready for a re-draw, given the number of useful comments so far...
Maybe JN could so a version to reflect the RF considerations voiced? (will he has the cad / ppt or whatever original...) :)
It'd be easier to continue the dialogue that way?
 
I suspect it's about ready for a re-draw, given the number of useful comments so far...
Maybe JN could so a version to reflect the RF considerations voiced? (will he has the cad / ppt or whatever original...) :)
It'd be easier to continue the dialogue that way?
It's a Visio file. I drew it about three computers ago so would have to dig.
Perhaps bill will start a thread with the orig, and as it's pulled apart it can be updated. I feel the discussion of what is wrong with it is valuable to anyone who wants to learn.
The other drawings are also important, as induction into the overall connected system was the impetus for the drawing being discussed.



John
 
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That triax shield question....first, def of centroid.. It is the effective center of a current going in one direction in a conductor. If it is uniform in a circular or rectangular conductor such as DC, it will be in the geometric center. I think of it as where the "mass" balances.

A send and return conductor loop current will attempt to go common centroid as frequency rises. In zip, the current distribution will get closer within the wires with frequency (crunching to one side of the copper), so uses less of the copper. This lowers inductance and raises effective resistance.

A coax already has a common centroid so does not change centroids with frequency. However, as frequency goes up, the core current will skin towards the surface of the core, and the shield will skin inwards towards the core.

So the double shield question is yes, outer shield skins in, inner skins out.
The question is, can the shields and wires be arranged such that any rf carried has all it's send and return current confined to the two shields? If that can be done, any current level will be magnetically cancelled external to the shields regardless of how much rf current is there. If it's really really large enough to cause an rf IR drop in the shield wiring, a simple shield over that bonded at star would fight e field. But if it's strong enough to cause an IR drop, you don't want to connect it at both ends as that will create a shared parallel path for the outer shield's current. That also means the inner core signal wires would require an additional e field shield to stop capacitive coupling. Current induced magfield cancellation at any cross section only works if the currents are equal and opposite and they have a common centroid.
John
Ah, ps.. I have assumed the lengths of wires in the chassis are very small compared to the rf wavelengths.

If it were easy, I' be selling French fries...
 
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I meant quantization. So say your signal peak is 3.3 bits. That is recorded by the ADC as 3 bits. You have an error of 0.3. No reconstruction filter will fix this.

You are correct, thank you. It was late, obvisouly. The problem in the example I gave was that I didn't specify there has to be enough noise in the signal before quantizing to effectively dither it before bit depth reduction (truncation or quantization, in the examples). So, my low-bit-resolution ADC example was for quantize (or truncate) before dither. For a signal already contaminated with sufficient random noise (or an otherwise suitable dither signal), my example would have been correct. The missing information you point out would have been buried in noise.
 
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Thanks George, but it's useless without the .wav files! ;) (But, really, thanks for hunting the old discussion down. And it's a good exercise for the user to generate they're own files anyhow)

Regarding the loss of wav files, it wasn’t deliberate.
But they weren’t unique either. Everyone can make them.
The whole discussion was informative.

George
 
The term "listening test results" for their reviewers is a bit unspecific but if you meant the usual tests done by audiologists, is there any evidence that better perceptual evalution abilities are mainly caused by differences audiology tests can detect?


I won’t use the word better, but altered and likely in these cases poor.

I don’t think any of us or any of their staff have remotely as good hearing as they believe themselves to have. I’d be interested to see it on paper.

Remember, a better ability to pick out something in a certain range (sensitivity) may be evidence of a hearing problem, not a super power.

Depends on the test battery, but yes. However, audiology has become a bit like dentistry, they aren’t exactly pushing the envelope. It’s certainly possible though. Autism research has provided the most new findings on human hearing in the last ~2 decades.

Again, I’d read up on recruitment and associated phenomena. Also autistic spectrum hearing related disorders.

We know a lot less about human hearing than many here assume.

I think you are giving yourselves far too much credit.

Is anyone here under the age of 30? 20? Then you might have a fighting chance.

Same as vision, it’s in a dramatic state of decay by now for most here.
 
I have data to prove I have crap ears
Actual hearing examination results of your hearing.




"All in one" has at least the potential to:
(1)minimize ground loop problems
(2)properly interface one unit to another (impedances, signal level),
(3)minimize the number of interconnection plugs and cables
As space has already mentioned, the issue of boredom after but can be handled.



Brilliant George thank you!

IMG_9881.JPG

So if ones ears measure worse than an old Heathkit scope thrown down a stairwell, what are we REALLY talking about here? (No offense George ;-) )

This is starting to feel like I’m in the funhouse.

The only people who can actually appreciate most of these nuances of amplifier designs have around $2.50 of disposable income and may still believe in Santa Claus.

By the time they can afford any of it, it doesn’t matter.
 
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So if ones ears measure worse than an old Heathkit scope thrown down a stairwell, what are we REALLY talking about here? (No offense George ;-) )

It’s all right, no worries but for the scope of discussion two remarks:
- I am not a representative case here (harsh work environment and some deliberate abuse)
- The brain learns to adapt to progressively developing hearing aberrations but that's only up to a point.

George
 
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