trying to understand dual voltage...

[foxfire]

i built this, http://www.muzique.com/schem/wah2.gif. i want to wire it up like any other pedal. i'd like to add a led and wire the battery/batteries so i don't have to worry about them. right now i have +9 and -9 going to pins 8 and 4 respectively and i have the ground lead going to the sleeve of the input jack. does that sound right? as for the led i'm not sure where to get power from? i'm not sure if i should treat the 2 batteries as one or not? i tried googling it but, i didn't come up with anything i could make sense of. thanks, rylan

[R.G.]

The drawing leaves aside any detail about switching the power on and off. You can't really treat the two batteries as one with the circuit as it stands. Dual power supplies are just that - two power supplies.

There are a couple of ways you can do this, but safest is to switch both batteries. If you leave one battery connected between its power and ground terminals, there are some circuits which will eat current from the connected battery even when the other one is open.

I designed one way to do this with ordinary bipolar transistors; it's at GEO, http://geofex.com/FX_images/splitter.gif. The stuff enclosed by the dotted line is the dual-battery switching. It looks complicated, but isn't really all that tough. It senses when the ring terminal of a stereo jack is connected to ground by a mono jack, and pulls the bases of the two NPNs high. That turns them on solidly. One of the NPNs connects the (-) of the lower side battery to V-; the other NPN turns on the PNP solidly by pulling down on its base, and the PNP connects the (+) side of the top battery to V+.

There are other ways. A slide or toggle switch with two poles works, of course, but it's not automatic with plugging in a cord.

You could put in a single 9V battery and use a MAX1044 or 7662 and create the -9V from the +9V so you only have to switch the +9V.

There are many ways to go about this. But you begin to see why dual voltages are not found all that often in effects.

[davent]

Hello,

I've built a bunch of little headphone amps using the Texas Instruments TLE2426 (or discreet equivalents) to create a dual supply. It's in a TO-92 package so takes up no room and no problem suppling current to a few op-amps. Should be able to  switch it with the usual input jack setup.


Take care
dave

[foxfire]

thank you both for your easy to follow suggestions. R.G. i knew you would have had something already out there i just couldn't find it. ok so now for the led. can i just steal juice from the +9 going to pin 8? although that somehow doesn't seem right though as i assume i want both halves as equal as possible? i'm starting to think i should just build Tim E.'s gargleton.

not that i want to give up on this one cause i do like what it does and, i'm learning new things because of it.

[davent]

Hello,

I've built a bunch of little headphone amps using the Texas Instruments TLE2426 (or discreet equivalents) to create a dual supply. It's in a TO-92 package so takes up no room and no problem suppling current to a few op-amps. Should be able to  switch it with the usual input jack setup.


Take care
dave

Hello again,

Upon further reflection I think you would need to use a seperate power switch to work with the TLE2426. So not what you were looking for.

You could put the LED between the +9v and the -9v with an appropriate dropping resistor.

dave

[R.G.]

ok so now for the led. can i just steal juice from the +9 going to pin 8? although that somehow doesn't seem right though as i assume i want both halves as equal as possible?

Yes, you can steal from the +9V. Yes, you do want them as equal as practical. If you run the LED from +9 to -9, both halves are more equal, but it gets complicated to turn on and off.

[foxfire]

thanks again R.G. so for what it's worth i'll go the easy route on this one.