Using a Charge Pump and a Voltage Control/Devolt

[liquids]

I'm working on a mini-booster/SRPP overdrive pedal (I know, yawn), and from some of my expiriments, I found that in an ideal world, I'd like to integrate a charge pump into the design,  AND a continuously variable voltage/bias control.   I was tinkering with it last night, but preliminarily had trouble getting it working the way I'd like.  So I thought I would ask for some help.

I'll reference these concepts as background for what I've tried so far:
http://www.beavisaudio.com/Projects/DBS/
http://www.muzique.com/news/mini-booster-fat-and-fatter/

A bare bones explanation of the topology I'm working with is a jfet buffer stage-->two cascaded SRPP stages--->volume control-->op amp buffer-->op amp active filter-->out.

My ideal situation would be to have my power supply feeding a charge pump (LT1054) doubling my voltage to ~18v and offering me about 100ma of current.  This voltage supply would be the voltage 'source' feed the op amps and the buffer all the time, for the highest possible headroom in those parts of the circuit.

From the 18v supply, I would then like to connect a 'devolt' type control solely to feed the two mini-boosters, in hopes that I could get a range from ~18v into to low voltages  (6v or so), continuously variable via a pot.  

So I started with a 500k pot, and I fed the 18v supply to one side of the pot, the other side of the pot with a 150k resistor going to ground (just for starters) and used the wiper to feed the SRPP stages, wired as a voltage divider.

Using my DMM and turning the pot the voltage quickly went for 18v to about 6v with just about 1/8 turn!  So I replaced the pot with the a 10k pot thinking smaller might be better....and still, I basically got the same thing.   There was little to no usable range...and I was very disoriented that 18v feeding a 10k pot + 150k to ground 'voltage divider' would yield mostly voltages below 6 volts....?

So I hastily abandoned this, and 'moved on' to eliminating the charge pump, feeding everything (op amps, buffers, etc) with my 9v power supply.  Not unlike what I linked above from the AMZ blog, I used various combination of diodes to feed just the SRPP stages a voltages between 9-6 volts.  This work brilliantly.  However, that configuration 1) eliminates the higher voltage ranges 2) only offers 3 voltage settings via on-off-on toggles 3) otherwise would require a rather large 1P/12T rotary switch to really implement this concept and utilize the whole range of 18-6v.

Note that my experimenting was all on the breadboard....I realize it could simply have been due to errors, or the nature of the breadboard to some degree...and I'll continue to experiment, however, if anyone has any insight, here are my questions:

1) It seems my values in the first configuration would greatly favor positive voltages...is the charge pump going to give me inherent trouble in this regard?  

2) Are my issues with the 'devolt' pot possibly because I am feeding different parts of the circuit different supply voltages?

3) should I instead replace the devolt with series resistance rather than wired as a voltage divider, and if so, could this cause load issues for the 100ma LT1054 18v supply feeding the op amps etc?

4) Is there a better way to do this than what I've mentioned above?    

[Processaurus]

Voltage dividers get saggy if they supply a load that is more than 1/10th the current they are drawing to ground through the divider,  I'm guessing the miniboosters drew more than that...

current through the divider: V=IR, 18v=I(10K pot +150K resistor to ground), 18v/170K= .1mA

Appropriate current for the load of that divider = .1mA/10= .01mA

Probably the boosters draw more than that and load it down, and in a weird way that loads it more when it's making signal.

Here's a solution, use a dual opamp, and use the spare side as an adjustable voltage regulator, like some designs use for the V 1/2 supply.  You would feed your pot hooked to 18v's wiper to the non inverting input, then hook the output up to the inverting input, as a standard buffer.  Then there is a low impedance version of the voltage you're making with the pot, that can directly supply the mini boosters.  

The only limitation to this approach is how much current the opamp can source, no matter what though I think your mini boosters would be fine, a couple mA at most.  I couldn't immediately see what the TL072's max current out was by glancing at the data sheet, but  the lofi workhorse LM358/LM324 can provide enough current to light an LED (20mA) no problem.

[liquids]

Genious!  Thank you.