Two questions about +/-9V power supply -RG, anybody?

[vortex]

Howdy, I've built quite a few pedals that required a basic 9V supply and have just started with a project that required both  + and - voltage power supply. The project is specifying +/-15VDC but +/-9V seems to work well enough.  I am an electronic lightweight but feel free to slam me with the "facts"!

I have searched around a fair bit here and on the net trying to educate myself about power supplies and know that I am quite unknowledgable (and hesitant for safety reasons). In the +/-15V range the transformer/regulator circuit seems the popular way to go.  Making the purchase of the right transformer for the job has proven a bit daunting for me, none of the resources I have found on the net have been specific in detailing buy Digikey/Mouser part # so and so.... I feel competant in hooking up and mounting parts if the information is clear. I have searched a fair bit through catalogues and on the web and have yet to find specific info that I felt  I could successfully and safely build .

There really seems to be a big jump in the topology between the circuits that provide +/-9 volts to a project ( MAX1044 Charge Pump for one) and  +/-15 V. I understand how regulators work and feel comfortable with that. Still, I keep looking at my thrift store 9V wall wart adaptors and thinking that I could use two 9V wall warts and avoid the "transformer" expense/uncertainty.(I know that wall warts contain transformers...) I get a bit concerned before I mess with AC.
I do plan to buy a few MAX1044 IC's and experiment with them. In the mean time, I have used the "old school" Mutron Envelope filter dual battery supply to get the circuit up and running and it is working well.

So my two questions, so far...
1) What is the best/simplest way to add a switch to power on/off the circuit?
2) Can I use two 9V wall warts wired similarily to the batteries in the image below to power the circuit?

Any insights/info greatly appreciated!

[Paul Perry (Frostwave)]

You will need two switches to connect the battery. That is to say, a switch with two on-off poles. One to control the +9 to the board & one for the -9. Note that there is no use just lifting the ground connection, because you will still have curreent flowing through the system (though, your bias will be weird!).

And yeah, two plugpacks connected similarly will work.
Note that circuits vary in how sensitive they are to having the+9 and -9 being not exactly the same voltage. For our stuff, they are usually remarkably forgiving.

[zeta55]

Check out R.G:s single battery option for tne Neutron filter

www.geofex.com/PCB_layouts/Layouts/neutronpub.pdf

/Krister

[smnm]

here's a spazzy drawing  that shows how to use a dpdt switch to connect the batteries to the single ground

[R.G.]

I am an electronic lightweight but feel free to slam me with the "facts"!

Actually, that was a thoughtful, well presented question that indicates you won't be a lightweight for long.

I have searched around a fair bit here and on the net trying to educate myself about power supplies and know that I am quite unknowledgable (and hesitant for safety reasons).

That's smart. The AC power line side is quite dangerous if you don't know what you're doing.

In the +/-15V range the transformer/regulator circuit seems the popular way to go.  Making the purchase of the right transformer for the job has proven a bit daunting for me, none of the resources I have found on the net have been specific in detailing buy Digikey/Mouser part # so and so.... I feel competant in hooking up and mounting parts if the information is clear. I have searched a fair bit through catalogues and on the web and have yet to find specific info that I felt  I could successfully and safely build .

That's true. The "Power Supplies Basics" article at GEO does not have a specific power transformer listed. I think it has most of the rest, except possibly for the AC power line safety issues. Here's the scoop: for a +/- 15V supply for, say, 100ma for one pedal, you need a transformer that makes at least +/- 18Vdc for the regulators to operate. That turns out to be a 32Vac centertapped output or two 16Vac windings. You might get away with a 30Vct or two 15Vac secondaries because low power transformers are notorious for running a bit high on voltage at lower loads.

A suitable transformer at Mouser is the Hammond 546-229A30, about $13.00. It's a flat pack intended for PCB use, though. For ones with leads, you could use the 546-166F30 or 546-166G30, both about $15.00. These bolt down and have wire leads.

However, as it shows in "Power Supplies Basics" at GEO, you can make a single transformer produce both +/- outputs by doing two half wave rectified sides. This means you'll have to put in much bigger power filter caps to keep power ripply down, but since you're regulating, this should not be a problem. a suitable transformer for this is Mouser 415-215042, 15Vac, 400ma.

There really seems to be a big jump in the topology between the circuits that provide +/-9 volts to a project ( MAX1044 Charge Pump for one) and  +/-15 V. I understand how regulators work and feel comfortable with that. Still, I keep looking at my thrift store 9V wall wart adaptors and thinking that I could use two 9V wall warts and avoid the "transformer" expense/uncertainty.(I know that wall warts contain transformers...) I get a bit concerned before I mess with AC.

Smart. A little knowledge is a dangerous thing. Be sure you have enough of it before starting something that could kill you.

1) What is the best/simplest way to add a switch to power on/off the circuit?
2)Can I use two 9V wall warts wired similarily to the batteries in the image below to power the circuit?

Simplest? Plug the two 9V warts into a power strip and switch the power strip.
Best depends entirely on what you're trying to do. A double pole toggle switch or rocker switch works fine. Unless you use semiconductors or a relay to switch two lines from one activation switch, you need two poles. Cheapest is the multi-transistor circuit I showed at GEO.

In a multivoltage power supply, you must either switch the AC power in, or use one switch pole per voltage to turn off all the voltages.

[MartyMart]

Easy way for 2 batteries is to use 2 x stereo jack sockets for I/O one has - batt lead
as normal the other has the + batt lead, so plugging in both I/O cables powers the circuit.
I used this on my LHX2 JCM800 sim and they have lasted a LONG time

MM.

[caress]

you can also wire the pedal up without true bypass but with a single 3pdt.

[switch 1/4/7, 2/5/8, 3/6/9]

                    O1     O2     O3
                   
                    O4     O5     O6

                    O7     O8     O9

1 - ouptut jack
2 - nothing
3 - nothing
4 - input jack
5 - 9V + 1 to board
6 - 9V + 2 to board
7 - board input
8 - 9V + 1 to battery
9 - 9V + 2 to battery

then send the out from the board directly to the ouput jack and wire the led + to the 9V + on the switch that you're using for positive power.  a little confusing, but it works well...

[g3rmanium]

In the +/-15V range the transformer/regulator circuit seems the popular way to go.

I have some experience with the XP Power DC/DC converters. I'm using the IA0515S in my squarer prototype.

[vortex]

Wow! Many many thanks to all who took the time to reply. This is great info for me. It's starting to make sense. Now I get to hurry up and wait for parts to arrive...

I am going to check out the Max1044, it seems like the easiest way to get +/- 9 volts in a small space.

I did build this circuit http://www.electronic-circuits-diagrams.com/psimages/1.gif based on a NE555 chip. Sure enough it provided  both + and - voltage from a 9V battery. When I hooked it up to my project there was a loud high pitched whine on the output.

I am also going to make a supply with the Hammond 229A30 PCB tranny RG suggested. The data sheet is located here http://www.hammondmfg.com/229.htm . Near the bottom of the webpage there is a link to a Pdf with the connection information for the 229A30. I am still not 100% on how to hook up the secondary windings. Any advice appreciated.

Thanks again!

[MartyMart]

Be careful of the MAX1044, it will only supply around 10Ma, so anything more than a simple
fuzz/overdrive will require more current !!
There are some more robust chips, just do a search

MM.