get -18v from 9v for total recall?

[senoravocado]

Hello everyone! I had a quick question. I was wanting to do a dual pedal that had a Total Recall and some type of reverb in it, maybe a Moodring. Since they have different power requirements (The Total Recall needs 24v positive ground and the Moodring 9v negative ground) I was curious on the feasibility of it. I did read in the build docs that it could be possible to use a 18v supply for the Totall Recall if I lowered the value of the resistor in series with the power (R57 I believe) from 240R to 22R So I was thinking of possibly using a charge pump somehow and then flipping the wires to get the -18v i would need for the Totall Recall. I just dont know if this could introduce issues or is something that is remotely possible.  It would just be very awesome if I could have one power jack that would daisy chain with my other pedals nicely. Any thoughts would be very much welcomed!

[blearyeyes]

Check out the Road Rage PCB at the bottom of the Madbean Projects Page.  Don't know about dealing with the ground scheme of the box.

[madbean]

Won't work. The two different power requirements are not compatible for using a voltage inverter. IOW, you cannot feed -18v into a charge pump to get 9v out and you cannot feed +18v into a charge pump because it will fry. Maybe there is some other type of voltage inverter out there that is capable of it, but the 1044, LT1054 definitely are not.

[senoravocado]

Madbean - Sorry I should have expanded on my thought a little more. Since I know that it is possible to power the Total Recall with a 18v power supply, I was wanting to use a regular 9v power supply into a voltage inverter to get it to be -9v (as if I was trying to power a PNP fuzzface and have it daisy chain with the other pedals) , and then put the -9v into a charge pump to get -18v. Does that make more sense? So 9v -> -9v -> -18v

So my thought is that this would allow me to use the 9v in the beginning for the Moodring, and then the -18v at the end of the charge pump madness would power the Total Recall.

Blearyeyes – I was looking at the roadrage board and saw that It could act as a charge pump, but I didn't know if it could work with a positive ground effect. Thank you for pointing it out!

[madbean]

It is possible to use two charge pumps to convert a 9v supply into -18v, however there are several reasons not to do so. 1) possible heterodyning/noise when using it for an audio application that also uses a clock (like the TR uses to drive the BBD), 2) sufficient output current available from the two charge pump configuration to run the effect (maybe? I don't know for sure) and 3) the conversion is not efficient, you will likely end up with something more like -17.5v and you need a supply with a solid -18v to use the LM7915 to get a steady -15v operation needed for the TR. IOW, two charge pumps + a regulator doesn't seem too promising.

But, it would only take a few minutes to breadboard the power supply scheme and see if it works with the TR. I just can't say that it will. This shows how to do it for a TC1044, but the same should work with an LT1054.

[senoravocado]

Thank you for the schematic Madbean! I do not have any LT1054 chips handy, but I will definitely breadboard it when I get the chance and report back on my findings.

I was trying to think of other ways to achieve the -18v from 9v and thought since the -18v is supposed to be regulated to -15v in the end, would it be possible to make a bipolar power supply that outputs -15v and 15v (like the ones that are in eurorack modules I believe) and just use the -15v part and bypass the regulator? It seems like a sound idea but I am just brainstorming right now.

[skeeter]

Build Brians Total recall with -24v,   and also try OP Electronics 9v deluxe memory man for your 2 pedal build if you go with the 3205 option like I did you can't go above 9v,but if you use the xvive 3005 you can go up to 12v ,I have populated my total recall but not finished it ,the OP MMD went into a 12 pedal multi effects box, it works great!!! size is smallish not very large and has 2 modulation switches,Brians aquaboy is a brilliant delay try one  for 2 pedals in a box as well.