BiPolar Power supply for op amp?

[Team Toothpaste]

Hello all. I was wondering if anyone could help me. Basically I've done a lot of work lately with CMOS stuff, building oscillators and whatnot, I'd like to progress on to some op-amp circuits but aside from the 2 x 9v batteries trick,I can't figure out how to power them. I'd like to power it from the mains so I can leave it on in a gallery for a few hours a day and not worry about the batteries running down. Is there some way to do this with a guitar pedal style power supply (possibly using a voltage divider or something), or should I be using, say a 0-18v supply and setting up some kind of pseudo ghost ground type thing at 9v. This gap in my knowledge is really impeding my progress and I'm sure some of you probably know exactly what I need to hear to clear things up.

Thanks in advance for any replies.

[andrewF]

check out the MFOS wallwart bipolar PSU
(select from the list on the left)

[egasimus]

Power the opamps from VCC and tie them to ground at 0V.

Then, make a 1:1 resistor divider, with one end to VCC and one end to GND. 10k-47k resistors are fine, as you won't really be drawing any current here. You can use smaller values, too, but that would result in considerable amounts of current flow to ground, effectively wasting precious power.

The junction of the voltage divider (where the two resistors connect) will be at VCC/2. Now, connect that to the opamp's non-inverting input (if using several opamps in a circuit, do this through resistors - say, 100k). The signal goes to the inverting input. On the output you get a signal which is inverted in phase and with +VCC/2 bias added. However, the entire waveform is now preserved, and not just the positive-going part.

At the opamp's output use a suitably large capacitor to remove the DC bias. There you go.

[PickNick]

TLC272?

[Team Toothpaste]

thanks guys, these are all good suggestions.

andrewF - there's a lot to look at on MFOS, all good stuff. I don't feel confident with the idea of building my own power supply just yet as I haven't done anything other than 9v projects.

egasimus - your answer was confusing at first as I have learned only basic electronics with some very basic theory, but reading it through really slowly and a little bit of googling and it makes sense - so thanks for that. Just for clarification, when you say "one end to VCC and one end to GND" could this apply to something like a guitar pedal wallwart such as a PSU for multiple guitar pedals such as http://www.guitarsplusmore.com/proddetail.php?prod=SUPERCHARGER

PickNick - the TLC272 looks interesting, is there a reason this kind of op-amp is less commonly used in hobbyist projects? I haven't heard of it before but it seems like a good solution

thanks again guys - sorry for the amateurish questions, your help an patience is appreciated

[bubzy]

You could try lm7809 and a lm7909 you may need two power supplies for this if you are using the "wall wart" type. or a 24v CT transformer if you want to make a proper power supply.

also check out this
http://www.nutsvolts.com/media-files/11/January%201998%20Thomas%20Henry%20-%20Power%20Supplies%20for%20Electronic%20Music.pdf

i have this power supply and it works very nicely, theres a 5v circuit underneath which with a little modification and reading of datasheets, you could easily convert to 9v.

someone can correct me if im wrong, but if you want to use this circuit with wall transformers that already output DC voltage then the bridge rectifier(the 4 diodes in a triangle) wont be required.

-bubzy (also a newbie to electronics)

[egasimus]

Yes, VCC and GND are your positive supply and ground - if you power your device from a power supply intended for guitar pedals, those would most probably be the sleeve and tip of the plug.

You should definitely get a good power supply for developing stuff - I hate not having one. An old PC power supply has plenty of power and outputs four voltages: +5V, -5V, +12V and -12V. It's regulated, and it's usually pretty well filtered so it wouldn't make your circuits hum.

[PHOBoS]

[PrimateSynthesis]

I'm not sure what you are trying to do, but if you need to build a bipolar supply from +9V DC, because biasing a single-sided amp with Vcc/2 won't work, then you could use something such as a TC1044 to get -9V. If you look around you can find little PCB's already available for stomp box builders. Although it's simple enough to build on a generic project board.

[PickNick]

yep!
but they say one MAX1044 board per one Stompbox...
the output is about 20-30mA...
http://www.aronnelson.com/DIYFiles/up/bipolar_power.pdf