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previous: Adam Ziegler LM386-1 Chip for Active Pickups? -- 11/12/2002 1:17 AM View Thread

General opamp notes

11/13/2002 5:47 PM
Dr. Strangelove
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General opamp notes
ne of the early problems with EMG pickups was their reliance on a mediocre opamp (National Semi LF441?) in order to get acceptable battery life.  
 
Many opamps draw too much current for use in active pickups, often needing 4-8 ma to stay alive while the average carbon-zinc battery has a 400 ma-Hour capacity -- 100 hours is the very best you can hope for from one cheap battery.  
 
Eveready's 9V batteries have these capacities:  
400 maH - carbon-zinc  
565 maH - Alkaline A522  
655 maH - Energizer E2  
1200 maH - Energizer Lithium  
 
If possible, select the opamp for 1-2 ma quiescent current and remember that you need 2-3 pickups in a guitar. Avoid them.  
 
Finding a good-sounding low power opamp will take time because the lowest current opamps often have poor bandwidth, distortion, and noise qualities.  
 
A rough selection guide could be:  
8+ Mhz GBP (gain-bandwidth product)  
4+ Mhz unity gain bandwidth  
<1-2 ma quiescent current  
<200 nv/hz noise voltage  
5-30 volts supply voltage  
 
As audiophile opamps go, these figures aren't impressive, but they are the compromise you must make if you want more than 10 hours on one battery.  
 
-drh  
--

 
Replies:
Adam Ziegler Dr. Strangelove Thanks for ... -- 11/14/2002 4:13 PM
Dr. Strangelove More opamp notes -- 11/15/2002 5:36 PM