How to power Craig Anderton mid-boost by a 9V battery?

[Carlos]

Hi!

This may seem incredibly stupid to you, but I don't know how to convert the Craig Anderton mid-boost from a +9V/-9V supply to a +9V battery.

how would you do it?

regards

Carlos

[cd]

Two options: either use a MAX1044 chip to get +/-9V (see www.geofex.com) or usea +/-4.5V supply. For the latter, you know the usual 10k splitter found on most pedals?  If you ground the 4.5V supply (middle of the two 10k resistors), then the +9V becomes +4.5V, and the old ground becomes -4.5V.

[Mark Hammer]

Whether wisely or unwisely so, Jack only posted PART of the original schematic.  What he has shown has actually been *adapted* to use a bipolar supply.  The original schematic (also found in the yellow DIY projects for guitarists book) shows a Vref provided by the usual pair of 10k resistors and a medium-value cap (10uf or so) going from the junction of those resistors to ground.

So, +9v goes to two 10k resistors in series to ground.  A 10uf cap from the junction of those two resistors to ground (+ end at the junction).  The on/off switch now goes to the Vref instead of the chassis/true ground.  

Note as well that since Jack redesigned it to simply be an insertable resonant boost rather than a standalone effect pedal, the terminating resistance has been omitted in the drawing.  The original had a 10k pot from between the 2u2 output cap and ground, although you could also use a simple 10k resistor (or not) depending on where you planned on inserting it)..

[spongebob]

The voltage divider can be used to create a virtual ground for the feedback loop, but don't forget that the signal that is fed into this circuit must also have a DC offset of Vref, otherwise half of your signal will be clipped.

You could take a dual opamp and configure the first half as a simple buffer (with Rin going to Vref/voltage divider), or is there a simpler solution?

[Mark Hammer]

Actually, what you describe is the other "missing part" of the original schematic.  Anderton used a LF353 dual op-amp for this, with one half configured for a unity gain, non-inverting input buffer.  The + pin of that op-amp section was tied to the Vref through a medium-high value resistor (probably 470k or something) and a DC blocking cap was feeding the input of that op-amp section.