Bipolar supply

[Electric_Death]

So let me get this straight with simple bias power supply circuit


I'm still not sure how to use this thing. Does the 4.5 actually go to ground and my +/- are wired accordingly to my op amp?

I'm under the impression I should in fact be building this:



Right now I'm using the 2 9 volt method but need to due away with this technique for a few reasons, the primary two being enclosure size and the voltage doubling and tripling circuits I've started working with.

[jrem]

well, close . . .  you do have + and - 4.5 vdc, but really what you have is 0, 4.5, and 9 vdc.  The 0 and 9 run the op amp, the 4.5 is the reference voltage for the signal.  This allows the ac signal to 'swing' between the 0 and 9, instead of hitting a rail on half the cycle.

get it?

[slacker]

Those 2 are basically the same. The difference is just where you've decided ground is and measured your voltages from.
In the top one ground is the battery negative so that give 0, +4.5 and +9 in the bottom one you've decided that ground is the junction of the 2 resistors so measuring from there gives -4.5, 0 an + 4.5.

If you decided that ground was battery positve you'd have a negative supply giving 0, -4.5 and -9.

For opamp circuits you just connect + supply to the highest voltage and - supply to the lowest voltage, then the middle one is used to bias the opamp to the middle of the 2 supply voltages.

[Mark Hammer]

ideally, the signal swings between the maximum possible achievable voltage (+9v) and whatever the lowest possible achievable voltage is.  If the supply were actually double-ended (e.g., +/-9v) the two extremes would be the two supply voltages, with ground being the midpoint.

When you power the circuit from a single-ended supply (battery or wallwart), you have to pretend there is a midpoint, and the pretend midpoint is most often designated as whatever half of the supply voltage is.  If the supply voltage is +9v then the pretend midpoint is +4.5v.  If the supply voltage is +12v, then the pretend midpoint is +6v, and so on.

In the diagram you've shown, the midpoint is provided by simply using a resistive divider (10k + 10k) that cuts the supply voltage in half at the junction of the two equal-value resistors.  The actual value of the resistors will depend on how much current you need to be able to supply.  So a pair of 22k resistors would also provide +4.5v, but with less current available for whatever needs the 4.5v "pretend ground".  (Actually, that doesn't sound quite right, does it?  )

The 4.7uf cap is there because some things do need to see a stable ground, and since the pretend ground is impacted on by other parts of the circuit "wanting" current at +9v, the cap is there to essentially stabilize the pretend ground and make it behave like a resolute, unchanging level.

The 2nd diagram you show is more or less the same thing as the first except the labels are throwing you off.  If you re-labelled -4.5v as ground and connected it to ground, then relabelled +4.5v as 9v and connectedit to +9v, and called the midpoint Vref and connected it everywhere you would normally see Vref or Vb in a circuit, it would work pretty much exactly like the first diagram, except that a second cap is added to stabilize the other end of the supply.

[head_spaz]

TheToneGod offers this valuable resource, and he explains things much better than I could.
Converting Opamps to work in Signal or Split Supplies
It might help, for all intents and purposes, to consider your new ref at 4.5V to be GROUND. It is commonly known as a VIRTUAL-GROUND.
It also goes by the term bootstrapping.
The idea is to split a single ended supply voltage into a bipolar supply, with a (lifted) virtual-ground in the middle. As far as your circuit is concerned, your new rails are RELATIVE to virtual-ground, meaning virtual-ground in the middle becomes the reference.
The circuit interprets this midpoint (4.5V) as zero volts... relatively speaking.. The 4.5V below this artifical zero is then negative.

Be sure to check out Texas Instruments' TLE2426 rail splitter. Some good reading there too. The TLE2426 is a nifty little rail-splitter (still available in T0-92) with a built-in resistor divider and buffer. The built-in divider network is very high impedance to minimize battery drain, and the opamp buffer inside is able to supply much more current on demand than a simple resistor network. All this in a three lead package. It's a very efficient little device that's cheap and easy to employ. Perfect little gizmo for stompboxes.

Hope ya'll find this information useful.
Best Regards...

[jrem]

Be sure to check out Texas Instruments' TLE2426 rail splitter.

well, now, that ain't bad, but for a buck fiddy I'll save my money, throw two four-cent resistors in there, and burn off the power from a wall wart.

oh there I go again, not being green . . .

[Electric_Death]

As I recall, I initiated this post in the Beginners section....

Anyway, great answers, if you love reading your own posts, but I'm just looking to get the thing to powering up my circuits.
Maybe none of you have kids or beginner students but you should try using less ego derived mumbo jumbo and more direction when someone asks you a question that has a simple answer. Telling someone how to hook up a circuit they don't quite understand isn't the same as simply letting them copy your homework and isn't going to inhibit their learning.
It will actually accelerate it. You learn far more by doing than you do studying.

I just wanted the thing to work, meanwhile it's been 3-4 years of fighting, with people who generally initiate the fights in the first place, to have made very little progress. I came to DIY sites asking straight forward questions but generally, the seasoned regs are so board(and I often assume jobless or working low demand jobs) that provoking people then initiating a fight if the question seeker doesn't suck it up has been the norm on each and every single guitar and audio oriented diy forum.

I appreciate the answers and head_spaz, you basically gave the straight forward and much needed answer novices seek that so many, for reasons I can only assume are boredom and ego problems, deny majority of us.
Would it kill everyone that frequents DIY Audio, DIY Stomp Boxes and other assorted DIY guitar/audio oriented sites to be straight forward and give useful answers that actually help people move forward rather than beat around the bush and spin them in circles?

Most of us got into this craft because we can't afford to buy the gear we need and want, I have a hard time affording the parts and pieces just to build and experiment as it is.
I think an awful lot of people on the various DIY sites have forgotten this and demand unjustified humility from those seeking help. While I'm the least knowledgeable, I'm also the guy that will go to his grave knowing that some of my unique innovations were straight up ripped off by guys in the industry that many of you call friends.

I'm not trying to get any of you worked up but I also know many of you know exactly what I'm talking about because you've been on one side of these things or the other and for those that have stuck around long enough, it's been both. If I could have paid to go to school and avoided the childishness I've been treated with the last 3-4 years, clearly based on my progress, pitfalls and encountered irreverence I would have done so. I actually understand most of what was said but what beginner simply looking to power up their first circuit will?
Absolutely none and I have to say, the way I've been provoked and treated in general on these message boards is absolutely shameful leading to a half dozen message board names on each. I'm legendary for humiliated people on countless forums but it was never my intentions, the web is just full of people acting like jerks, whether they are in person or not. I've been helping people my whole life, I never insisted they let me treat them like crap before doing so.

Humility needs to be shown if it's expected to be given.

[slacker]

As I recall, I initiated this post in the Beginners section....

Didn't know that, it was in here when I replied. As to the rest of your rant I think you must be reading a different thread to me I can't see anything wrong with any of the replies.
Maybe they weren't the answers you wanted but I can say for definite that I don't have any ego about this I do it for fun, I honestly thought I was giving a useful answer to your question. I'd say the same goes for everyone else who answered.

[gez]

And the Strangest Thread of the Year Award goes to...

To the original poster.  Unfortunately, it's sometimes difficult to gauge people's experience/understanding when answering posts as this medium is faceless and many members come and go, so remembering what level they're at can be awkward.  Perhaps you're not getting the answers you wanted, but the solution is simple: quote what it is that is confusing you and ask that person (or others) to elaborate in simpler terms.  It also helps if you give a little more detail: post a link to the schematic you're trying to adapt, for example.

Nothing in any of the posts I've read above was anything other than fellow Forumites trying to be helpful.