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Weird customer problem need help


 
4/8/2005 2:22 AM
Dave Stephens Weird customer problem need help
Well here we go again, another new problem to solve, something new to learn (damnit.....). If any of you know what causes this I'd appreciate some help here. Here is the customer's email:  
 
"I just had the pickups installed at Stringmasters custom shop .They explained to me they could not fiquare out why in positions (two) and (four) output level is cut in half and in these positions the tone is horrible. When the pickups are ran individually .Position 1 , 3 ,5 they  
 
sound fine....."  
 
 
 
I have a set of test pickups I wound with completely different wire on the same premade bobbins, the magnets are alnico five and metric fatter sizes, magnets are taped, and wound with plain enamel. His guitar is a 50th anniv strat, mine is a Chinese squire. The problem is the same, the output drops in the inbetween positions in 2 and 4. Doesn't sound "horrible" as he says, the volume just drops noticeably. These aren't hot wound pickups, nothing over 6K or under 5K. Pickups individually sound awesome, something weird is happening in these two positions and I don't have a clue what is going on here. The stagger is modern, almost follows the radius of fingerboard but not quite. freaking weird.......
 
4/8/2005 2:24 AM
Dave Stephens
I forgot to mention that the problem is the same whether I use Essex heavy formvar or plain enamel from Korea, I don't think its the wire...
 
4/8/2005 2:33 AM
Dave Stephens
one thought, the magnets in these are pretty strong, I wonder if that could be causing this....
 
4/8/2005 3:35 AM
Josh Pardes
email

That's a good one. How much does the volume drop?
 
4/8/2005 5:26 AM
Dave Stephens
I"d say about 70%, very noticeable...
 
4/8/2005 6:56 AM
Joe Gwinn
email

On 4/8/2005 11:26 AM, Dave Stephens said:  
quote:
"I'd say about 70%, very noticeable..."
I assume you mean 70% as estimated by ear, versus measured by voltmeter. If you mean by ear, then the electrical cancellation is quite good. Assuming that your ear is well calibrated, with traceability to the National Bureau of Standards, we can estimate the degree of electical balance necessary to achieve this:  
 
Perceived loudness is proportional to the logarithm of the signal power, and a 3 decibel change is barely noticable. In round numbers, a 10 decibel change in signal power is heard as a doubling or halving of the loudness.  
 
By 70%, you are basically saying that the loudness at least halved, so the signal power dropped by at least 10 decibels.  
 
The formula for decibels is Pdb = 20*Log10[voltage].  
 
So, the coil voltages must be matched to within 10=20*Log10[voltage], or voltage= 0.301.  
 
In other words, the difference between the two coil voltages must be less than 30% of the average of the two voltages. The actual cancellation is probably a bit better than this, as the loudness drop was greater than 50%. In either case, that's pretty good for accidental cancellation.  
 
My bet is that one of the coils is wired backwards, or a set of magnets is reversed.
 
4/8/2005 2:20 PM
Steve A.
email

Joe said:  
 
My bet is that one of the coils is wired backwards, or a set of magnets is reversed.  
 
    That would be an exclusive "or"... you would want both conditions to be true for a RWRP middle pickup (which is advertised on Dave's site).  
 
Steve Ahola
 
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