9V Single/Mid Power Supply

All amplifiers use the same power supply configuration. This consists of a 9V battery with an active mid-supply (powered by an op-amp). Most popular ICs are available in single-supply power configurations, from 3V to 12V or so. However, most also require a driven mid-supply that can sink or source some current. Thus, a 9V battery plus active mid-supply is usually sufficient to power most electronics. Note that just about any op-amp can be used to drive the mid supply, but this op-amp itself must run from a single supply.

Schematic

This power supply produces 3 outputs: V+ (9V), V- (0V), and V0 (usually 4.5V). These lines are referenced from all other schematics, and are usually provided in the circuit by physical buses (see photos). Note that none of these voltages is regulated, although that kind of hardware could be added. Generally the chips used in these circuits are fairly insensitive to small changes in power supply voltages. Also note that for most purposes (e.g. epochal analysis of signal data), supply values will drift very little. Finally, manual or auto calibration (offset and gain) can be included as part of the final circuits.


Individual Chip Bypass

In addition to the V+, V-, and V0 supply lines, each IC in an amplifier is individually "bypassed" by 1 or 2 capacitors as close as possible to the chip across the V+ and V- pins in the following way:

All chips are usually configured this way, in spite of their data sheet instructions. In some cases (e.g. National MF10), powering chips according to the data sheet can introduce noise into the system (e.g. a 300 KHz ring). Therefore, the default configuration for all power is as above. Neither the line supply, nor the chip bypass, will be shown in subsequent schematics.


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