Power supply voltage with voltage doublers and stacked opamps.

[Asymmetric]

Recently I've been wondering about the voltages most pedals are run on. As far as most pedals go, I generally prefer the sound of 18v opposed to the traditional 9v. To me, it just sounds clearer and more articulated. I build all my pedals with parts (including the opamps) rated for 18v+, so I was wondering; if I have all my capacitors rated for 40v+, and two opamps stacked rated for 18v each, could I run a voltage doubler like this
http://www.sabrotone.com/wp-content/uploads/2012/12/VoltageDoublerLT1054.gif

but for 18v to 36v? Are their any circuits like this, but for 9v to 36v? I never use batteries, so battery life wouldn't be a problem!
I really like my opamps to have a lot of headroom, so experimenting with voltages and ic stacking seems interesting.

[djp8djp]

If you'll be handling signals at guitar-output strength, or at what one finds in the vast majority of stompboxes, then 18V is already more than enough. That'll give you a swing of +/-9V if you can go rail-to-rail capacity, or say +/-8V if not. Either way, that's more than enough. So there's no point in going to 36V. If you're using this as a clipping unit that's further voltage-bounded, then even less so.

"More is better" only gets you so far. If you're building a house and plan on accommodating a lot of 7-foot tall guests, building your ceilings at 8or9 feet is sufficient. Building them at 15 feet doesn't gain you anything. Same goes for voltage ranges in opamps - if you have sufficient headroom at 9V, then 18V won't be any better. And perhaps not everything on your board(s) will take 36V? In which case you'll also need 18V or 9V. And perhaps not one Vref, but two. A lot more complexity there too, for no advantage (caveat - that I know of).

So for this application, you might as well save the extra cost of the 36V-capable opamps, and spend it elsewhere. As for your stacking, I don't know for sure, but I think that the voltage output will remain in the neighborhood of the larger opamp, but your current output capacity increases. Maybe I've got that part wrong - someone with more stacking experience could probably say for sure.

[djp8djp]

ps - here's a recent thread with a situation where +/-18V would be useful.
http://www.diystompboxes.com/smfforum/index.php?topic=114209.0

[R.G.]

- Yes, there are circuits to make +/-18V or 36V from 9V. It is possible to convert any power voltage to any other voltage if you are willing to spend the effort and circuit complexity to do it. The single-IC charge pump is a special case to make one of these situations easy.
- There are existing power supplies in a single lump to transform one DC voltage to another. Mouser sells an assortment of DC-DC converter modules that will take in 9Vdc and output +/-12V or +/-15V. They cost in the range of $10-$30 depending on the power and manufacturer.
- +/- 18V would be a better choice than +36V, as it simplifies the reference voltage setup. It will require un-winding the special cases and circuitry to make a Vref for a 9V only pedal, though.
- As noted, you may not need 36V. There really is a point of diminishing returns on almost everything. A guitar amp can only "eat" about 2V peak at its input before the input is overloaded and no further voltage change will make the input tube change its plate voltage. Pro audio stuff is rated in dbm, which is db with respect to 1mW in 600 ohms, about 1Vrms, 1.414V peak. +/-14V peaks are +20dbm, and this is a level outside what most pro studio gear will tolerate without distortion. It is more common to use ±12V to ±15, as noted below.
- Most of the opamps used in pedals will run at +/-18V. In particular the TL07x series will. You have to get used to looking up the manufacturer's datasheet on the parts you use. You don't need to stack opamps to get to 36V, and in most cases this would not help anyway. Stacking opamps may increase current as noted, but it does not increase the voltage capability of the opamps.
- However, it's common to use +/-12V or +/-15V for opamps which are not forced to use +9Vdc for power. In the electronics world, single +9V power is the oddity, not +/-15V. Bipolar supplies let you use ground for a reference. This is what most opamps are designed for in the first place.