Negative voltage circuit or device from DC

Hi all.

I was wondering if there is a way to make a variable negative voltage circuit. Im planning on building a multi output bench power supply using a PC PSU. I know they typically have a -12V output, but was wondering if there is any other form of circuit or device that can take a +5V or +12V out and convert that to anywhere between -2V and -35V. I an still learning about PSU's and work with audio components that require anywhere between -20V and -3V on their negative rail. (I'm still studying).

I can probably build something with an LM337 negative voltage regulator with a trim-pot (can regulate up to -37V as far as I know), but wouldn't know how to go about getting the voltage up to that using a -12V DC line on the PC PSU. I would like to keep everything coming from the PC PSU. Thanks!

You can apply 12v+ to this little block and it will output -3 to -15v.

To accurately dial in the voltages you want, you'll need a few pots in series (possibly a switch for each in parallel to override since you'll need a very wide dynamic range of resistances to go from -3v to -15v.