Power active pickups/stompboxes with AA's

nianri6 · Post by **nianri6** » 13 Sep 2011, 03:20

I recently made myself a charge pump circuit that fit inside my guitar with active pickups that runs off of 2 AA batteries, and can supply both 9 and 18 volts, and it lasts slightly longer than a standard 9 volt battery. My prototype has a 9 volt connector on it, wired backwards, so that it can be plugged into an existing active setup. Would there be a market for this? The board would pay for itself within the first year of use, since AA's are so much cheaper than a high quality 9V.

ansil · Post by **ansil** » 13 Sep 2011, 08:26

yeah very nice lets have a look

nianri6 · Post by **nianri6** » 13 Sep 2011, 12:08

I'll upload pictures of the board I made sometime later tonight. If there's enough interest in it I'll get some PCB's made.

RnFR · Post by **RnFR** » 13 Sep 2011, 12:40

how about a schematic?

nianri6 · Post by **nianri6** » 13 Sep 2011, 20:38

I'm working on an electronic copy right now. It works just like the MAX1044 but without the 20ma supply limit, and is much cheaper too. I'm not 100% sure if it can create negative voltages like the MAX1044 can, that's my next project. I was able to create this with 4 transistors, and the limit to the amount of current it can supply depends entirely on the two output transistors as well as the battery of course. Schematic will be up shortly.

nianri6 · Post by **nianri6** » 14 Sep 2011, 04:11

: 3v-9v V.2.bmp (176.94 KiB) Viewed 1462 times

This is my first schematic post so I'm sure I screwed something up, but if you scroll straight down on the picture I attached, you'll see the schematic. Anyway, C1 and C2 control how fast the circuit oscillates, I chose to go with the smallest value I had on hand to make sure the ripple created would not be audible. A smoothing capacitor would not be a bad idea. Anyway, all 4 transistors I used were 2n3904's, which can supply more than enough current for this circuit and are extremely cheap. All diodes are miscellaneous Schottky diodes. C3-C8 are all 4.7 uF non-polarized. All resistors are dependent on the voltage supply, they drop the voltage to .7 volts. I just now realized I forgot the 4th resistor on Q4, sorry about that. Simply adding another 2 diodes and 2 capacitors will add another 3 volts to the output, minus the voltage drops from the diodes.

ansil · Post by **ansil** » 15 Sep 2011, 07:18

ok its late but i get the osc and the charge pump but usually when you use this type of diode ladder each stage doubles the voltage supply you put in so unless i read this wrong we get 21v minus the diode drop which is schottky which usually is around .3 so that is like 1.8 v so 19.2v or am i just sleepy????? it is late and i worked ten hours at the joe job so i think i will clean the ole glasses and sleep on it and look at it tomorrow.

nice clean circuit though thanks a ton for sharing.

ed

nianri6 · Post by **nianri6** » 15 Sep 2011, 12:39

Each stage is made up of 2 capacitors and 2 diodes, so it's around 9 volts (minus voltage drops) rather than 21 volts.

ansil · Post by **ansil** » 18 Sep 2011, 05:16

ok that makes much more sense sorry don't know how i missed that lol guess i was half asleep as usual

going to build it though got to order some parts from small bear soon

nianri6 · Post by **nianri6** » 18 Sep 2011, 13:50

Hey, it happens to all of us lol. Also, you'd probably want to add a fourth stage, using schottky's you'd get 9.9 volts from 4 stages, and 7.2 volts from 3 stages like it is in the schematic. I wasn't counting the voltage drop in my schematic.

And if you buy from small bear, the part of the circuit that works like the MAX1044 will cost about $1.50 to make, as opposed to over $3 for the chip. And it can output 10x more power. I'm working on getting this to generate negative voltages as well. I'll post a new schematic of how to do that when I work everything out.