John Curl's Blowtorch preamplifier part II - Page 1757 - diyAudio
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Old 4th November 2011, 03:06 PM   #17561
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by simon7000 View Post
It is quite possible to build A/D's that are bandwidth limited to meet 24 or more bits. The most common application is in digital scales.
Hey, I worked with those in the 80's. The actually at the time most precise and lowest drift solution we had at the time in the "100 Tons" class where classic mechnical balances with an attachment that rotated optical code disks. The microgram scales for the lab where all electronic digital of course.

Quote:
Originally Posted by simon7000 View Post
Those freakin capsules are way too cheap. If only someone would publish a nice preamp circuit to go with them.
I believe those capsules need a polarisation voltage, I would have to check how much. Difficult to do cleanly from 48V phantom power, well, there are 1MHz switchers these days, I would need to check if they can work in boost configuration...

For a preamp circuit, the common standard these days is a pair of PNP Emitter followers which use the phantom power resistors in the Mike Pre/Desk as loads, suitably biased, with their collectors supplying a zenner diode which in turn supplies a J-Fet that operates as Buffer and Concertina Phase Splitter. I believe this originated with Georg Neumann GMBH.

Scott Helmke's Alice is a good example:

Click the image to open in full size.

As you can see, shooting for super low noise is pointless, actually some people tried 2SK170 and even 2SK147, they generally have lower output and more noise, due to their high capacitance, FET noise is much less important than low capacitance.

One can probably use a non-phantom power standard scheme with more current and other optimisations to lower noise, but the capsules capacitance is one of the main factors limiting noise.

Personally, I'd probably get Jonathan Billington to make me a transformer I can put straight into the source of a suitable cascoded J-Fet, this would minimise both noise and parts count. But such a transformer would probably NOT be cheap...

Ciao T
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Old 4th November 2011, 03:15 PM   #17562
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Quote:
Originally Posted by ThorstenL View Post
Hi,



Splitter. I believe this originated with Georg Neumann GMBH.

Scott Helmke's Alice is a good example:

Ciao T
Jorg Wuttke of Schoeps. An all FET version with SJ74's works too, gets rid of numerous problems and allows very nice film caps for the coupling. I think these capsules are designed for optimum tension at 60V. You can generate 60v from 3V without an oscillator (buy it off the shelf too). I don't want to give away too much now.
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Old 4th November 2011, 03:19 PM   #17563
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Scott,

Quote:
Originally Posted by scott wurcer View Post
Thorsten, re: your 1" plus 1/4" capsule idea, is it like a two way speaker? If the 1/4" is for a smooth high end then considering its self noise is dominant there why is that not a problem.
First, the noise of the mike capsules falls with frequency, actually, to be precise, the noise of the load resistor gets lower as frequency rises because the capsules capacitance creates a lower impedance shunt across the resistor...

Second, hence, while the smaller size (and capacitance) capsule will have more noise at low frequencies, I suspect by 500 Hz or so things should be low enough to not loose a lot of sleep...

What I would worry about is if I can get a seamless enough crossover...

Heck, we probably could make a 2" capsule then...

Ciao T
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Old 4th November 2011, 03:29 PM   #17564
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What about the self-noise of the capsule?
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Old 4th November 2011, 04:55 PM   #17565
Jakob2 is offline Jakob2  Germany
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Quote:
Originally Posted by SY View Post
If you mean "interchannel time delay," then yes, that's exactly what I was asking for. Doesn't have to be music, test signals are fine as well.
Interchannel time delay is a more general phrase that covers ITD as the specific phrase for the ear as channel .

Frindle reported ~11s and Holman ~10s in an article.

As the topic is closely related to AB microphonic setups, there exists a plethora of research papers with (as usual ) diverging results.

I havnt seen so far a research paper in which delays as small as 10s were used, but given the graphs it would map for an mimimum audible angle of 1 degree to a ITD of ~12s, see:

http://www.uni-koeln.de/phil-fak/muwi/ag/tec/lok.pdf

Unfortunately written in german.
The Author researched the dependance of localization effects from loudspeaker quality.
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Old 4th November 2011, 05:02 PM   #17566
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Quote:
Originally Posted by SY View Post
What about the self-noise of the capsule?
Or free download, B&K Technical Review No. 3 1972 excellent derivation from first principles (anything that references Landau and Lifshitz is cool)
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Last edited by scott wurcer; 4th November 2011 at 05:25 PM.
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Old 4th November 2011, 05:05 PM   #17567
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First principles strike again.
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Old 4th November 2011, 06:19 PM   #17568
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Quote:
Originally Posted by chrissugar View Post
EXACTLY!


the product between speed and accuracy is constantchrissugar
Of course, in case folks didn't notice this is simply a rephrasing of the heisenberg uncertainty principle. Audio is tinkering with the laws of physics again. There is a Heisenberg limit for A/D's and D/A's and we are not even close yet.
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Last edited by scott wurcer; 4th November 2011 at 06:21 PM.
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Old 4th November 2011, 06:24 PM   #17569
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Hi,

Quote:
Originally Posted by scott wurcer View Post
Jorg Wuttke of Schoeps. An all FET version with SJ74's works too, gets rid of numerous problems and allows very nice film caps for the coupling.
Really? I used 2SJ109. Works well.

Quote:
Originally Posted by scott wurcer View Post
I think these capsules are designed for optimum tension at 60V. You can generate 60v from 3V without an oscillator (buy it off the shelf too). I don't want to give away too much now.
Well, 60V is not too bad. I remember some that where quite a bit higher.

Ciao T
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Old 4th November 2011, 06:26 PM   #17570
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Originally Posted by SY View Post
What about the self-noise of the capsule?
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