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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
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.  

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