quote: ""Voltage Regulator:...The LP2951CN is an 8-pin plastic DIP" Any 5V regulator will do. I used a 7805L, but the LP2950/2951 is much more rugged."

The 7805 is also a bit too large electrically, and actually may have trouble regulating so little current. Which is why I went for a micropower regulator.  

 
[QUOTE]"One can also see the music signal on the field, as the bandwidth of the A1321 is DC to 30 KHz." Then you can calculate the delta-Gauss that's driving the pickup from the amplitude of the AC component.  
 
That 'delta-Gauss' vs. pickup output looks like a good place to start in characterizing pickup sensitivity, especially since no pickup manufacturer has ever admitted to doing so.[/QUOTE]One can certainly determine the pickup sensitivity in terms of volts out for a given change in magnetic field (volts/delta-gauss).  
 
The higher the frequency, the lower this ratio, due to the increased impact of eddy currents at higher frequencies.  
 
One can also test a pickup's sensitivity by putting an air-core coil near the pickup and driving the air-core coil at 1000 Hz, measuring the ratio of voltage out to drive voltage in. The existence of the DC magnetic field will have no effect.  
 
I don't know that I believe that it's a conspiracy of silence though. More likely, they just strummed a test and rated it by ear.  
 
Now that I think about it, it seems that what would need to be measured would be voltage out for a given mechanical amplitude of string vibration. The classic way to measure this would be to pull a string away from its rest position by a standard distance, say 3mm, and let it go abruptly. The initial voltage gives the effective sensitivity. (Of course, the amplitude will vary with distance from string to pickup coil, so this distance would need to be standardized, say to the thickness of a US Nickel coin, which is 1.8mm.)

 

quote: ""The A3515 noise is 400 microvolts RMS, while the A1321 noise is 40 millivolts peak-to-peak." Read closely. The 3515 gets their 400 rms with 1/10 the capacitance on the output."

Yes, probably to cut those spikes down a bit, so rms values wouldn't be too deceptive.  
 
However, a 10:1 difference in capacitor load doesn't full explain a 40/0.4= 100:1 difference in reported noise level. My guess is that the noise level is actually more or less the same, and what we are seeing is the effect of different measurement approaches. I think I'll just get a couple of each kind, and compare them.  
 
That is, if I can get any A3515s. If I recall, Newark didn't have any. Maybe they have A1301s and A1302s, which claim far better noise performance. But, it doesn't really matter. The real question is how much noise the A1323 yields, and how much it matters.  

 
[QUOTE]"The 7805 is also a bit too large electrically,..." The 7800 series is/was available in 3 basic flavors: L,M,H = low, medium, high ~ 100ma, 1A, 5A. The L/M/H is in different places depending on manuf.  
 
The 7805L is the low current version. The 7-10ma load represented by the either Hall effect sensor is adequately handled within the 100ma limit of the 7805.[/QUOTE]OK. National has deprecated the 7805L, but there are probably other makers. The other reason to use LP2951 was that I wanted to be able to adjust the voltage, rather than being fixed at 5 volts nominal. One can force a 7805 to do this, but it's easier with a regulator intended for the purpose.  

 

quote: ""I don't know that I believe that it's a conspiracy of silence though. More likely, they just strummed a test and rated it by ear." We have a century of transducer technology in which they are specified by an input-output model, variable reluctance sensors among them. Guitar pickups are very conspicuous by the absolute lack of such data for them. If not a conspiracy of silence, then sloth or ignorance surely suffice."

I agree. Sloth and ignorance are by far the more common. Conspiracy is simply too much work.  
 
In all my readings of pickup patents, I've never seen anything more precise than loose talk about more efficient magnetic circuits, and I have never seen anyone hang a number on "more efficient". I guess that there never was enough of a reason to care, or someone would have done it, and patented it, or at least discussed it in a patent.  
 
Another likely reason for the lack of precision is that people rate pickups by their loudness to the ear, and the minimum humanly perceptable difference is something like 3 decibels, or 2:1 on power (1.4:1 on voltage), so only fairly large differences are going to matter. Said another way, the magnetic circuit plus windings would have to be a factor of 1.4 better to even be noticed.  

 

quote: "Consider this an opportunity to exactly characterize the magnetic perturbation at the string and to correlate it with the transducer output, i.e., shoot off your mouth where no gadgeteer has done so before."

But, wouldn't that violate the conspiracy?  
 
Seriously, the mechanical motion to electrical output ratio is variable, depending on the spacing between strings and poles, which musicians adjust to taste.  
 
When this is taken with the factor of 1.4 discussed above, it's not clear how much precision is really necessary and achievable.