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Introduction to Op-Amps - Part 3
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Please be aware that this discussion is aimed at the Pro-Audio area, and is not intended for Audiophiles or other areas of circuit design outside of the Pro-Audio environment. The concepts are generally the same, if not identical. However the topic area is vast and the intent of this discussion is quick and effective practical usage - not theory, advanced or extremely high end systems.
Powering your Op-Amp Circuit with Batteries
Batteries have the benefit that they are pure voltage and are not converted from AC (Alternating Current) - this eliminates the potential of adding noise in the form of 50 hZ or 60 hZ from your AC line. Batteries also allow you to move away from other power sources. This can be handy if you create something thats built into an instrument, or needs to be carried along as part of a wireless rig. If you are making outdoor videos, this could prove very handy. The downside is that batteries have a limited lifetime, and their power often drops off to unusable levels just when you need them most.Op-Amp circuits can be designed using low power chips that greatly improve the life of batteries. Choosing larger resistor values when you work out ratios for gains can also reduce current flow. Its hard to know which is the best choice without building it first, and sometimes you find that the power requirements are higher than you want. You can always use rechargable batteries (NiCad and NiMh cost a lot more, but they can be recharged hundreds of times).
You really need at least 6 volts (+ 3 Volts and - 3 volts) to use an Op-Amp at all. If using 1 1/2 volt Alkaline batteries, this would equate to 2 batteries for the + supply and 2 batteries for the - supply. You could also use a single 9 volt battery, with a simple voltage divider to simulate + 4.5 volts and - 4.5 volts. For battery only power supplies, I prefer two 9 volt batteries, because it gives the circuit more potential life as the batteries start going dead.
The multi-battery solutions require a DPST (Double Pole, Single Throw) switch to disable the batteries when not in use. This is more expensive and in general more trouble than many people want. Later, if you decide to use a battery eliminator (AC Power), you'll need 2 battery eliminators.
In general, you'll usually find something like 1 Battery Power Supply the most commonly used method with battery powered equipment. With it, you can easily build in a battery eliminator jack.
Questions? Comments? .
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