Merlin 'Valve Wizard' has designed a pedal to push tube amps......

[frequencycentral]

Merlin is the man. He is Valve Wizard: http://www.freewebs.com/valvewizard/ He's just linked me to this pedal that he's designed. This is all I know: "I have been breadboarding a buffer/booster pedal designed specifically for use on valve amps, which obtains up to 12Vp-p output swing from a 9V battery (a TubeScreamer on acid).". Beautiful looking pedal, I'm dying to hear how it sounds! I have no affiliation, other than that he used my graphics technique. 

[svstee]

Looks cool!

[Processaurus]

That is a very strange way of powering the opamp.

[earthtonesaudio]

Bootstrapped input resistor and power supply rails.  That's awesome.  Even more awesome would be to use a low power, rail-rail op amp (though finding one with a high enough supply voltage rating might be tough).

[PRR]

> That is a very strange way of powering the opamp.

It's covered in an old Burr-Brown application manual; my copy may be too yellowed to scan.

It is used in an obscure dBx limiter, to pump 25V peaks from +/-15V rails and op-amp.

I'm thinking that a good choke-loaded JFET or BJT and a 9V supply can kick-up 12V peak-peak a whole lot simpler. Bandwidth and fidelity may be dubious, but that's not really the point here is it? Power consuption could be higher than TL072; depends how good a choke you can find. I was hallucinating a small 120VAC winding and flashing on 4mA consumption, but that may be this cold-virus talking.

As with almost all Merlin's stuff, it is very well thought out and ought to do what he wants. The only puzzle is why C2 R3 bootstrapping.... maybe the output buffer is sensitive to offset.

[PRR]

> low power, rail-rail op amp (though finding one with a high enough supply voltage rating might be tough).

If the goal is "12Vp-p", no simple 9V rail-rail plan will work. However two 9V batts with most any decent chip opamp will swing 12Vp-p no fuss nor muss. Even if your are somehow wedded to 9V systems, two batteries is easy to try (find out if your amp input really sounds different with 12Vp-p instead of ~~6Vp-p); then get one of those rail-doublers to make 18V from your 9V source.

[head_spaz]

Surely this pedal is meant to be the last device in the chain, plugged directly into a tube amp, but some honyok is gonna be surprised when they don't read the fine print and sees this thing doing a dick dance on any pedals following it.
That oughtta be good for a few laughs! Eh?
Let there be smoke!

[earthtonesaudio]

If the goal is "12Vp-p", no simple 9V rail-rail plan will work.

I didn't mean instead of the bootstrapping, I mean in addition to.  The op-amps suggested (TL07x/4558 etc) "waste" a couple volts of output swing, so if you used a rail-rail amp in this circuit, you'd get more than 12V out.  Just an efficiency thing.

[earthtonesaudio]

I just tried this "rail bootstrapping" technique (with a CA3140 op-amp).  I didn't measure except with my ears, but the bootstrapping appears to add both headroom and overall output volume.

[R.G.]

I wonder whether the straightforward approach of simply using an LT1054 to make -9V might not use about the same total price of components and/or board complexity, and/or might not be simpler to get running if your wizard badges are still in the mail.

[earthtonesaudio]

I wonder whether the straightforward approach of simply using an LT1054 to make -9V might not use about the same total price of components and/or board complexity, and/or might not be simpler to get running if your wizard badges are still in the mail.

I wondered the same thing.  Probably it would reduce complexity significantly, while improving most aspects of performance.  On the other hand the charge pump runs constantly, but the class B output stage is off until you need it, making it a little more "green." 
To really measure that, however, someone would have to calculate whether the energy saved over the life of the pedal is greater than the energy required to produce and use a few more (different) components.  That could turn out to be a pretty difficult calculation, so maybe just ballpark it and say the bootstrapped one is preferred for use with batteries?