What is it called?

You are looking for a passive volume control. Try the forums. You could read for days on this topic. Don't waste your time at Radio Shack.

Rat Shack actually has a nice volume pot, you will have to buy a little plastic box and some input and output jacks as well as some wire. If you are handy, you can build yourself a nice little one input passive preamp in less than an afternoon. I built one for a friend and he preferred it to his $1800.00 preamp. When you get a bit more scratch, you can replace the pot with a stepped attenuator for even greater transparency, upgrade the wire, jacks, etc.

Check out the Luminous Audio Axiom.

Good luck.

How much can you afford right now for a pre-amp? I have a Yamaha Pre-Amp C85 that is non-remote I could sell for 75.00 plus shipping. It has a decent phono stage plus 4-5 inputs. It's been a while since I have looked at it so memory is off a little but it is in original box w/manual.
Problem you ask? Yes a few broken RCA inputs but enough remain for a CDP, Tuner and maybe a third component.

Viridian has the best idea. If you can solder you can build a passive with Radio Shack parts for about $10 that will amaze you with how good it sounds.

Project Enclosure 3x2x1" $2.29
Catalog #: 270-1801

Phono (RCA) Jack, 4 pack $3.99
Catalog #: 274-346

100K Ohm Stereo Control $3.29
Catalog #: 271-1732

A little wire and solder and a knob if you wish and you are in business. I can email you instructions if you wish.