Hey all! I've finally assembled enough components to have a functioning rack with some good possibilities. I'm pretty much out of space in my first case. When I look at the calculated power consumption, I see this:
633 mA +12V | 346 mA -12V | 0 mA 5V
I'm using the uZeus power supply from Tiptop Audio, meaning I have at my disposal:
2000ma at +12v
500ma at -12v
170ma at +5v
It seems like I'm quickly approaching the end of the -12v space. However, it looks like I still have a good deal of +12v and all of my +5v.
Now, please forgive my ignorance of electrical engineering - I have two questions:
If I were to buy another case without a power supply, can I selectively look for modules that only use +12V and +5V?
Is it possible to convert modules from -12v to +12v? (IE with an adapter?)
Answer #1: yes. Also, if you start speccing your own power supplies, you can find plenty of supplies that output lots more current than many OEM Eurorack supplies. This is especially useful when dealing with a large build. Or, alternately, you can go with a prebuilt larger case that has beefy amperage ratings...they've gotten a little more common, with the advent of cabs such as the larger Pittsburgh units (they're actually Monorocket designs, if I remember right) or the new (and cheap!) Arturia RackBrutes. Finding +12 only units might be a bit of a pain; you're better working out staying under the uZeus's requirements in its cab unless you toss it out and get something with more 'beef', like a 4ms Row Power 40 or a Koma Strom+.
Answer #2. I wouldn't try it. The issue there is that the -12 circuitry is going to expect to see a 'neutral' on its ground plane, not +12. This would be the only actual solution, as you would have a lot of trouble repolarizing that bus due to that issue. One module might be fine with it, but a couple of others might smoke. Again, the real solution (that avoids even the hint of a catastrophic possibility) is to either stay within the uZeus's limits or jettison it for a beefier supply.
That being said, though...the -12 rail on the Tiptop isn't as overtaxed as you might think. I like to spec current draws at 2/3rds of the rated maximum, which for .5A comes out to 333 mA, which is about where you are at present. So the ultimate answer here might be 'do nothing, it's just fine that way'.
One last thing: if you're planning to spec out your own power distro design for a new case, two things have to be kept in mind:
1) While linear supplies offer very quiet, no-ripple DC, they're spendy and weigh quite a bit. So this means you'd likely be using switching supplies...but in that case, you have to be concerned about noise on your DC rails. In bog-simple analog modules, this might not be a problem, but if we're talking about analog-controlled digital, the noise factor could creep in due to the switching noise interfering with the DSP clocking and such. These things can also radiate noise, so the potential for power supply garbage getting into other subsystems (think audio lines and devices here) goes up. Be VERY careful about noise factors on switchers.
2) You're always safer by using filtered busboards. Even with the quietest linear DC supplies, some modules can still send crud back down their own DC feeds which get back into the rails and spread out that way to cause all sorts of annoyance. Filtering reduces this problem, and can also be useful to reduce switching supply crud. If that's not enough, there's also various methods of isolating the DC supplies via filtering, noise chokes, etc that can get more garbage off the rails. The optimal thing you're looking for here is to drop the noise across your audio to as low a figure as is possible, as that will be the most obvious path for it to get heard...but just as much, reducing noise also helps with module stability, especially when tuning stability is critical. I would suggest putting a 'scope on your DC rail feeds during any such build to look for ripple (very bad) or switching noise to see what courses of action, if any, you might take.