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This is an extension from a thread I created over at MuffWiggler. I'm working on figuring out a simple DIY way to get line and instrument level signals into my eurorack. Given the space constraints of my case, I'd like to do this externally. I'm not too new to DIY, but mainly from a guitar perspective so bipolar power issues are somewhat new.

Basically, I breadboarded up a TL074 opamp circuit that works fine (I'll quadruple it in the final product). I have it running off of 2x 9v batteries (in series) right now for bipolar power but I'd like to run it off of a wall wart, preferably at +/-12v to interface best with the euro. How do I go about doing this safely? Or is it possible to run it off a unipolar power supply somehow? Like a 24v wall wart? Or can the opamp circuit be configured to require unipolar power?

I did some searching on the forum and via Google and I'm still a bit stumped. Any help would be greatly appreciated.

You could grab a 24 volt supply and establish a virtual ground between the high and low end using some method outlined here: http://forum.allaboutcircuits.com/threa ... cle.13678/

I think a more elegant solution would be to eat up some panel space and built it into the modular, where your supply needs are already covered.

If you like simplicity: I've also used transformers to step signals around, comes in handy when you've got tubed stuff wanting ~70 volt range to sync & trigger, but that's a can of worms if you so much as nod toward the mojo tone crowd.

Yeah I'm kinda thinking the simplest, most efficient solution will just be to suck it up and lose the 4hp in my rack. Thanks for the advice. I'll keep digging more into it.

really simple solution is to get a DC 18v supply in your guitar rig and use a guitar pre you like. maybe a BS170 or maybe a TL072. You might be able to do it with off the shelf guitar pedals. the guitar pre is AC coupled on the output so it does not matter at all that you have a single supply +18v/0v. Euro is best to have +/-5v peak or less for audio signals. 18v will get you there. If you can find a 48v creation audio labs clean boost you should buy it immediately at any cost. It is out of production. 30+Db!

I actually threw together an MXR Microamp and an LPB last night, but only with 9v. It worked decently for line level but not for instrument. I have a 12v supply I could try it with, I just need to double check all the caps.

I don't think you will have a problem doing a quick test. 16v caps are fine to run on 18v if you are there to watch it. there is always a risk of failure over the voltage rating so do this at your own risk. The problem is heat more than voltage.