okay designers and layout artists ... this is my plea for more split rails

[midwayfair]

I keep seeing a bunch of projects with +18V on an op amp. Come on, guys, live a little. Split rail! It's fewer parts. It MORE headroom by at least a volt. It is every bit as easy. Plus you can do doublers on both rails and blow up some chips! Okay, let's not do the last one.

Discrete component circuits with charge pumps get a pass, because no one likes putting a trimpot on both the drain and source of a FET.* 

That's my rant for the day. Pies may be directed at my face. No rotten vegetables, please.

*But in all seriousness, I guess I could have done split rail with the Hamlet.

[GrindCustoms]

You could have simply post your rant in my built post

But for some enigmatic reasons, bi-polar charge pumps does'nt ALWAYS gives the best results.

Theorically it suppose too, but if my ears tell me the opposite, i won't go that way.

[Scruffie]

There is another acceptable reason, if you want to allow switching back to 9V instead of 18V (some people prefer the lower headroom, quite rightly, or may not have access/want to use a charge pump) you can skip a charge pump section in a doubled build but not in a split-rail build, unless you want to regulate down to 4.5V before hand which is a bit... well yeah.

[stecykmi]

most effects pedals are AC-coupled so split supplies aren't as important since biasing is decoupled between different circuit stages, making the circuit much easier to build since the power supply is greatly simplified. by comparison, synthesizer electronics uses far fewer decoupling caps and split rails is ubiquitous. that said circuits with many opamps might benefit greatly from a split supply, especially with headroom when not using rail-to-rail opamps (the TL072 isn't!).

if you're not looking for double voltage, split supply can be had cheaply and easily with rail splitter devices (like this TLE2426). these things split your V+ in half with next to no loss, giving you +/- (0.5)V+, ie +/-4.5 from +9. it only has a maximum current sink of 20mA, but that's enough for 4 or 3 TL072's.

[GrindCustoms]

most effects pedals are AC-coupled so split supplies aren't as important since biasing is decoupled between different circuit stages, making the circuit much easier to build since the power supply is greatly simplified. by comparison, synthesizer electronics uses far fewer decoupling caps and split rails is ubiquitous. that said circuits with many opamps might benefit greatly from a split supply, especially with headroom when not using rail-to-rail opamps (the TL072 isn't!).

if you're not looking for double voltage, split supply can be had cheaply and easily with rail splitter devices (like this TLE2426). these things split your V+ in half with next to no loss, giving you +/- (0.5)V+, ie +/-4.5 from +9. it only has a maximum current sink of 20mA, but that's enough for 4 or 3 TL072's.

Now that's interesting!

Sorry, but i might not understand correctly, would that rail splitter give a +9V and -9V or does the negative output gets lower like a voltage divider would do?

[stecykmi]

it operates like a voltage divider, yes.

that's a lot less useful than a charge pump derived split supply, but it's also _really_ cheap, only one tiny 3-terminal device. in the specs, it doesn't even need a filter capacitor o_O
i would probably use one, though, haha.

[GrindCustoms]

it operates like a voltage divider, yes.

that's a lot less useful than a charge pump derived split supply, but it's also _really_ cheap, only one tiny 3-terminal device. in the specs, it doesn't even need a filter capacitor o_O
i would probably use one, though, haha.

I'm adding some to my Mouser cart, just for the sake of trying.

Got couple pcb layouts with bipolar charge pump setup, would be quite easy to try it on those.

[culturejam]

I've almost bought those TO-92 "VREF makers" several times. For space savings, they are great. But, for $1.50 each, I can use two resistors and a cap for about 10 cents instead. And if I want to save space as well, smd resistors and caps are just as small as the TLE2426.

So from a cost basis, I usually can't justify it.

Another cheap way to get exactly 1/2 of the supply voltage is to use a LM386. The output voltage is always exactly one half of the supply voltage. I drew up a simple utility for breadboarding back in 2011. It is attached.

Beware, however, that the LM386L that Tayda sells does not output exactly 1/2 the voltage (it is slightly less). They also sell a regular LM386 that works just fine, but it's a few cents more.

[pickdropper]

most effects pedals are AC-coupled so split supplies aren't as important since biasing is decoupled between different circuit stages, making the circuit much easier to build since the power supply is greatly simplified. by comparison, synthesizer electronics uses far fewer decoupling caps and split rails is ubiquitous. that said circuits with many opamps might benefit greatly from a split supply, especially with headroom when not using rail-to-rail opamps (the TL072 isn't!).

if you're not looking for double voltage, split supply can be had cheaply and easily with rail splitter devices (like this TLE2426). these things split your V+ in half with next to no loss, giving you +/- (0.5)V+, ie +/-4.5 from +9. it only has a maximum current sink of 20mA, but that's enough for 4 or 3 TL072's.

Yeah, these are used in a lot of DIY headphone amps that have a virtual ground.  Handy little devices.

[RobA]

I love the TLE2426. There's more to them than just saving space for the generation of a reference voltage. They provide a more stable and better buffered than you get out of even using an op-amp to buffer the output of a resister based voltage reference. I've been using them a lot lately in several differential transistor based circuits I'm playing with.

One thing to note is that if you use them to actually split the rails and use the center as an actual ground, then you probably are going to need an isolated power supply or use it with a battery. That's not an issue that comes up when using the charge pumps.

Personally, I much prefer to use split rails when working with op-amps, particularly when the circuit involves multiple filters. But, I'd also like to avoid the use of charge pumps everywhere because they aren't without issues themselves. I've been playing with the RECOM and Murata DC/DC converters and so far I'm really happy with them. They come in +/-9V, +/-12V, and +/-15V varieties and they are dead clean. The only problem I've seen with them is that they don't have any that can take a 9V input. So, that would leave me needing to use a 5V input type. But, I'm really leaning towards just making the move to using a 5V input and using these and the single rail variants as well to build everything. It would also make it possible to use USB based power supplies and USB battery packs.

[juansolo]

I keep seeing a bunch of projects with +18V on an op amp. Come on, guys, live a little. Split rail! It's fewer parts. It MORE headroom by at least a volt. It is every bit as easy.

Did that on the Superjudge *smug*

[alanp]

Sounds like someone needs to move to synthdiy, and +12/-12 volts

[raulduke]

I agree it makes sense to have split rails with Opamp designs. No doubt 'bout that. Makes reading a schematic nice and clear too (like Alan P says, the synth stuff all use bi-polar).

Those VRef Ic's also look pretty neato. Seem to remember them being used in some Subdecay designs.

Like CJ says though, compated to the cost of a few R's and C's it just doesn't add up, and there is usually a spare op-amp stage with most circuit designs to buffer the Vref line.

I hope in the future the guitar pedal world will just ditch the 9V 'standard' and move onto something more appropriate (18V or +9/-9V). The only reason I know it is used is because of the PP3.

Batteries suck, so hopefully they will become less and less common with pedals (I still have to include a battery snap for most of my customer builds on request though).

[RobA]

I agree it makes sense to have split rails with Opamp designs. No doubt 'bout that. Makes reading a schematic nice and clear too (like Alan P says, the synth stuff all use bi-polar).

Those VRef Ic's also look pretty neato. Seem to remember them being used in some Subdecay designs.

Like CJ says though, compated to the cost of a few R's and C's it just doesn't add up, and there is usually a spare op-amp stage with most circuit designs to buffer the Vref line.

I hope in the future the guitar pedal world will just ditch the 9V 'standard' and move onto something more appropriate (18V or +9/-9V). The only reason I know it is used is because of the PP3.

Batteries suck, so hopefully they will become less and less common with pedals (I still have to include a battery snap for most of my customer builds on request though).

I really agree about wishing for a move past the silly 9V thing. I'd move to a +/-12 external power supply for my pedals if I could figure out a connector to carry the three voltages that would work with pedals. There are some out there, but they all seem to be huge. I've also been leaning towards moving to a rack mount system and then using a MIDI pedal to control everything.

[culturejam]

I love the TLE2426. There's more to them than just saving space for the generation of a reference voltage. They provide a more stable and better buffered than you get out of even using an op-amp to buffer the output of a resister based voltage reference.

I totally get that. But I can't think of a single time that VREF stability/stiffness was been an issue for a circuit I've worked on. Maybe I'm just lucky, or maybe I'm ignorant to the benefits. ??