Power supply question about a Stompbox Cookbook project.

[skiraly017]

Most of the projects in the Stompbox Cookbook run at 15v. However, this one confuses me a bit. A quote from the book...

"This project is optimized to run off a pair of 9V batteries."

Okay, that's clear enough and I get it. Next line...

"Significant departure from +/- 6.5 to +/- 10V is not recommended."

This is where I get confused. At first reading, when warning not to depart from 6.5V to 10V sounds like a single 9V power source is needed. But if this project was intended for 18V, then the acceptable range would be 11.5V to 28V which is a pretty big range. Does this sound like a possible typo? Looking for opinions. Thanks.

[Mark Hammer]

A pair of fresh "9v" alkaline batteries CAN actually provide up to +/-10v.  Indeed, many of the battery-operated projects that have been reprinted/scanned from Brazilian mags often list the battery supply as 10v.

At the other end, as batteries grow older with use, their output voltage declines along with current.  Of course, a great many circuits have such minimal current requirements that they can continue to function off the same battery or a long long time, such that even though the battery is incapable of delivering big spurts of current, the circuit will still get enough current to work.  The battery, meanwhile, may only be supplying7vdc or less.  One of the major instigators for developing the low-voltage MN32xx series of delay chips was that the battery could be regulated down to 5v to feed the chip, enabling a 9v battery to provide suitable power for the chip even as it dwindled to 8.5v, 8v, 7.5v, and 7v.  I had an onboard preamp on one of my guitars for years that I powered with a 9v, but it would continue to work even when the battery had dropped to 5v.

So, Boscorelli's advisory is that while the circuit is aimed at battery voltage levels, it is not aimed at LOW battery voltages.    Furthermore, it is calibrated to assume something that is not greater than +/-10v.  With respect to that second limit, there are few components suitable for guitar effects that I know of which will be damaged by supply voltages greater than 10v.  Certainly most op-amps are generally good to supplies of +/-15v and +/-18v, and CMOS is good to +15v.  Digital chips may not appreciate supply voltages higher than 10v but then from what I've seen, Boscorelli does not use such chips, and in any event they would necessarily be fed a regulated 5v from the existing supply.  So, my guess is that the circuit is set up to behave best within that supply range.

Make sense?

[skiraly017]

¡Muchas Gracias!