Single Supply Opamp

Hi all. I'm designing a circuit centered around an opamp, and am planning on using a single 9V or 18V supply (single polarity either way.) What's the best way to do this?

Most documents that I have read use V+ and GND, and bias the the input signal with either a voltage divider or zeners.

Is there a reason that you can't use a voltage divider and a virtual ground, giving the opamp +V/2 and -V/2? The input can then be left centered at 0V. I know that this works, but I have seen very few designs set up this way. What is wrong with it?

Generally speaking you can do this. I'm on my ipad and can't paste the link, but one of the big semiconductor manufacturers has a nice application note on single sided op amp circuits that describes the various approaches and pros/cons of each. I think it's Texas Instruments or maybe National.

You can do this with very small signals. It'll be a battery hog, though.

It's a little difficult finding schematics of pedals using op amps that don't use that method because nearly all pedals run from a single supply, right? Scroll down to the "re-house gone bad" thread on this forum and you'll find a schematic example of the Danelectro Transparent Overdrive. The reference voltage there is not at 1/2Vcc as their own design feature, but a great many pedals just use two 10K resistors and divide the Vcc in half.

That method is not a battery hog either - 0.5mA for a 1/2Vcc reference is consuming 0.00225 watts. That's nothing compared to what a single LED is going to draw.

That method is not a battery hog either - 0.5mA for a 1/2Vcc reference is consuming 0.00225 watts. That's nothing compared to what a single LED is going to draw.

Agreed, as long as all you're doing is powering 20K worth of resistors and an LED. Most pedals do quite a bit more. :mrgreen:

A great many pedals just use two 10K resistors and divide the Vcc in half.

That method is not a battery hog either - 0.5mA for a 1/2Vcc reference is consuming 0.00225 watts. That's nothing compared to what a single LED is going to draw.

I agree with FenderLover. I have used simple 10k or 33k voltage dividers for single sided op amp circuits that run for days (literally) on a 9-volt battery.

A nice trick...maybe the next step up in complexity, and not always necessary...is to buffer the output of the voltage divider with a simple op amp buffer, the output of which is also 4.5 V DC (or whatever the output of the voltage divider is).

Agreed, as long as all you're doing is powering 20K worth of resistors and an LED. Most pedals do quite a bit more. :mrgreen:

And I agree with dsutton24 here too. In other words...the complete circuit may darn well kill a battery in several hours or several days, but either way I think the voltage divider (or other approach) is typically not going to be a significant contributor to the total current drawn from the supply.

Generally speaking you can do this. I'm on my ipad and can't paste the link, but one of the big semiconductor manufacturers has a nice application note on single sided op amp circuits that describes the various approaches and pros/cons of each. I think it's Texas Instruments or maybe National.

I found this. It was TI. Just do a search for "single supply opamp" and you'll get it. Thanks!