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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 26th December 2012, 11:29 PM   #31791
SY is offline SY  United States
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John Curl's Blowtorch preamplifier part II
Define "accurate mike."
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Old 26th December 2012, 11:37 PM   #31792
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Originally Posted by john curl View Post
That is when you first found out about microphone impedance? Congratulations.
A condenser microphone is a capacitor, what are you trying to say (1928 I was not around then)? What is the noise on a capacitor? Well let's see, one classic text book technique is to integrate the noise on a parallel R C network from 0 to infinity and as R goes to infinity the answer is always KT/C. Guess what the spectrum looks like? This is OLD stuff.

Or what's the current noise of a resistor? Sqrt(4KT/R) gee what does that mean?
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Old 26th December 2012, 11:43 PM   #31793
scott wurcer is offline scott wurcer  United States
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I'll bow to your greater experience ... !

But, this does remind me ... it's impossible to get sensible measurements about mic distortion anywhere; yes, I know there's a special technique using face to face mics to do the job (?), but no-one actually specifies anything worthwhile of the results.

Or do they ... ?

Frank
You are talking about reciprocity which only works on some mics. Google will turn up lots of results. This is the accepted lab standards way (as well as the electrostatic actuator method). There is an obvious technique using two tones one coming from each of two speakers so the IM is only from the mic. With care this can be very good.
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Old 26th December 2012, 11:49 PM   #31794
scott wurcer is offline scott wurcer  United States
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Originally Posted by john curl View Post
Anybody yet figure out WHY B&K used such a low input Z?
They were making measurement insrtruments and it didn't matter. B&K technical journal 1972 recommends 10G Ohms BTW.
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Old 26th December 2012, 11:51 PM   #31795
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Originally Posted by scott wurcer View Post
You are talking about reciprocity which only works on some mics. Google will turn up lots of results. This is the accepted lab standards way (as well as the electrostatic actuator method). There is an obvious technique using two tones one coming from each of two speakers so the IM is only from the mic. With care this can be very good.
Yes, but who publishes results? A couple of times I hunted around, but all I came across was single figure "nonsense" and the like. What about full spectrum, at different levels, you know, "engineering stuff" ...

Frank
 
Old 27th December 2012, 01:02 AM   #31796
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No, they were worried about HUMIDITY! It is so good that you have known everything useful for just about forever, even before 1966. I didn't. I was still in the dark. I always try to credit my sources.
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Old 27th December 2012, 01:04 AM   #31797
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In 1972, I was seeking out 100G resistors. Chickened out using them, settled for 1G and 10G. Still have some.
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Old 27th December 2012, 01:05 AM   #31798
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Fas 42, it doesn't really matter. Start with a measurement mike and compare.
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Old 27th December 2012, 01:11 AM   #31799
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John Curl's Blowtorch preamplifier part II
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No, they were worried about HUMIDITY!
Even in 1966, the ways to deal with that were known. Electrometers used very high value resistors.
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Old 27th December 2012, 01:28 AM   #31800
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I did NOT create the B&K schematic that I had to upgrade. They did, AND they told me that this was the reason in 1973. Now for the resistors I still have left:
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