John Curl's Blowtorch preamplifier

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#4,701
KBK said:


GRollins: For the reproduction of the given DC works, you'd have to use pressurized/release-'positive' vibrational devices. Ie, single sided positive, like the human voice and the ear designed to hear it, or the voice designed to engage the ear. Hard to say on that one. But I'm sure that such is obvious after a few seconds of reflection.
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Don't misunderstand, it's not so much a question of reproducing DC, per se as it is getting the waveforms right. I don't know if the Linn people still make a big deal out of this point the way they used to, but with the exception of some classes of electronically generated waveforms, there's always a distinct ramping up at the beginning of any sound. In the process of accelerating from nothing to something, the sound actually transits from 0Hz up to the final fundamental.
You can truncate the low end and the music is still quite recognizable and nice to listen to, but it's missing a little bit. This is the inversion of the wide bandwidth thing up top. Neither is important taken on their own because we can't hear those frequencies directly, but they matter in terms of reconstructing the waveform.
The LP is mechanically limited, but it should be possible to get a reasonably good approximation of DC on any of the digital formats. The playback chain can handle it...well, sorta...you don't want to do that woofer forward-and-hold stunt at high power...but a lot of electronics can handle DC. The question then becomes one of getting the proper source material. That's when you run into trouble. Even if the electronics in the studio are all direct coupled (goodbye transformers!) the microphones are going to impose limits on the low end.
I suspect a microphone that was optimized for really low frequencies would be compromised in some way that would make it unsuitable for something like violin or vocals. You could arguably use two microphones in tandem, one to cover the normal range and one optimized for low end, then blend the signals. This would be analogous to the way a two way speaker splits the signal at the crossover then feeds separate signals to the tweeter and woofer. And you'd face exactly the same problems with phasing, relative levels, and coloration that you do in designing speakers. It wouldn't be easy. I'm not even sure that the cure wouldn't be worse than the disease. It's just something to think about, perhaps push towards even if you don't get all the way to DC.

Grey
 
#4,703
SY said:


In that case, your statement that the pressure doesn't go negative, by your definition, is wrong. It does, on the return of the cone to neutral.
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If you consider the 'hissss' that precedes a sonic boom, then comes the understanding a coupling point of the negative portion following a transient peak, then idea that the control of the following waveform shape does affect the transient that was er, in front of it. Subtle it may be, but the pre sonic boom 'hiss' provides the consideration that it is there. Some evidence of the indication of the possibility of such is found under the liquification issues of metals and the like when testing their 'speed of propagation'. That's mechanical, not electrical. But from my understanding and research on the connectivity of the two, the intimacy of the two on the molecular level is unmistakable.
 
#4,704
I think you are worrying too much, Grey. We dealt with this, decades ago. In the end, it is the sub-woofer that won't pass the waveform fidelity.
Special CD's have been made that go very low, BUT don't expect vinyl to do it properly, as it is next to impossible for good reasons.
Of course you could always get a Mickey Hart CD, a CD version of the 1812 overture, or the Sheffield drum record (direct disc only please) and find the limits of YOUR hi fi's low frequency response, but don't expect it in general.
 
#4,706
Actually, Newton is adequate to send probes to Pluto, and of course
until Relativity came along, was not contradicted.

And perhaps you could equally phrase it "Relativity still has problems
integrating to Quantum Mechanics".
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Dear Nelson, I'm not sure that I fully understand you. Newtonian Mechanics are in fact the so to say slow velocity limit of special relativity. For any speeds within a notable fraction of the vacuum speed of light you need to apply it to get correct results.

Of course with the simple methods available until the beginning of last century sufficiently correct observation was impossible.

I admit that I do not know sufficient details on sending probes into space, but thinking of the rocket equation and the speeds such probes develop when gravitational forces of planets are used to further accelerate it, it makes it plausible that one desparately needs to apply at the very least special relativity to avoid that a billion dollar journey into space does not become a desaster.

Further to correct things like the blue shift that happen when one is higher up in the gravity well than e.g. the earth (for comparison of data observed from the probe to data observed on earth or close to earth like Hubble), makes the application of general theory of relativity necessary as well. Also orbiting itself is affected by effects of gen. theory of relativity.

But maybe I just misunderstood you; of course Newtonian mechanics is sufficient to calculate a trajectory to Pluto in principle.

Only the question remains wether one is happy with the precision of the result - which I fear is the only sentence in my posting concerning amplifiers as well 😀

All the best, Hannes
 
#4,707
AKSA said:
SY,

This is a rarefaction only, a few pascals below the mean pressure of air at rest, and double that below the compressive peak. Were you thinking he meant a negative absolute pressure? Agree - that's not possible,
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Yes, it integrates out to zero; for every compression, there's a rarefaction, no matter what the drive to the speaker it. I still can't figure out what the heck he's talking about.
 
#4,709
Put a "battery" in series with "sine source", for example. Voltage of any battery is independent, you can set it for each of them.
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Thanks for the hint Pavel and of course I have tried a few different routes already which have been confirmed (somehow) along the way 😉.

Fellow designers, if someone would have told me 30 years ago that I would be in such good company here, I would not have believed him. Now 30 years later I'm happy to look back, smile and be thankful for everything I've learned along the way. Wonder what the next 30 years will bring 🙂.

Franklin
 
#4,710
SY said:


Wanna bet?

Take out a mike and do your experiment. Whaddaya know, when you disconnect the battery, the SPL waveform is negative. Huh!
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We listen to sounds in the time domain!

It doesn't matter what happens later. Both are audible in the time domain.
If you seek quality of sound reproduction, you'll maintain the original polarity.
Thus reproducing accurately the instrument, regardless of how it produces its wavefront.
 
#4,712
myhrrhleine said:
[snip]If you seek quality of sound reproduction, you'll maintain the original polarity.
Thus reproducing accurately the instrument, regardless of how it produces its wavefront.
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But how can we do that? We can *only* try to keep the right polarity from whatever it is at the mike position. We have no idea what the relationship is (phase-wise) between the instrument and the mike.

Jan Didden
 
#4,715
janneman said:
But how can we do that? We can *only* try to keep the right polarity from whatever it is at the mike position. We have no idea what the relationship is (phase-wise) between the instrument and the mike.
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myhrrhleine said:
Quality recordings will maintain polarity.
With others, it can be measured.
Last resort, use your ears.
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It seems that Jan is the one that understood what I meant a few posts ago and what started some rather useless word-fights (I'll always lose a word fight when some native speaker is using Schopenhauer's 38 stratagems).

@myhrrhleine:
How do you actually measure correct polarity of, say, a modern electric jazz combo (Fender Rhodes, Electric Bass, and Drums). By mere assumption of a positive attack of a kick drum hit? Do you have a database of "known correct" instrument samples which you take as a reference, when comparing waveforms (which is a very hard thing to do, IME).

I'm not a aware of much pro gear, ranging from mic-pre's, mixing desks, outboard devices, to the final ADC, master recorder or vinyl cutter that explicitely mention preserval of absolute polarity. Maybe it is considered self-evident that it does so, no need to state that then, but I'm by no means sure that this is a fact.


Or let's ask someone involved, that is, Mr. Curl:
Were the Crystal Clear Direct-to-Disc recordings made with correct polarity (I own one of the series, Charlie Byrd, CCS8002)

- Klaus
 
#4,716
To illustrate what waveforms seem to tell or not to tell:

Does this wavefrom look hard clipped?
 

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#4,719
Klaus, first, there are mike polarity identifiers (electronic instrument) available.
Second, Crystal Clear used B&K mikes (inverting) with my discrete mixer electronics, with an inverting mixer stage, so they could well be non-inverting, but I don't know about the disc cutter electronics (Ortofon).
If you really care, then you should ask John Meyer of Meyersound, as he was the technical engineer on the recordings He and I both knew and appreciated absolute polarity since 1974 (a long time ago).
Call him at Meyersound or e-mail him. He is located in Berkeley, CA, USA.
 
#4,720
I agree many/most recordings are a mess wrt polarity.

But I don't believe we should just give up.

This is the blowtorch thread.
Is polarity ever audible?y
Is correction or attention cost prohibitive ?n
Then lets pay attention to detail.

If you don't care, leave it off of your $10K Preamp. 🙂
Just give me a choice.

Personally, i prefer correct polarity over triple-0-nothing THD.
 
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