I have a very nice domestic CD player with line outs on unbalanced phono connectors, and I want to connect it to the balanced line input of a mixer. There are magical boxes that can take care of this (impedance, level and unbalanced-to-balanced conversion) but the only one I can find is the Sonifex RB-BL4. I'm sure it's great but it would be cheaper to buy a new CD player with balanced outputs! Can you recommend a similar unit for fewer pennies?
SOS Forum post
SOS Technical Editor Hugh Robjohns replies: The least expensive but decently performing box of this type that I'm aware of is the ART Cleanbox Pro, which costs around £70$80 — but it's really not necessary in your situation. If I were you, I'd just use a pair of RCA (phono) to mono jack-plug cables and get on with it! There are no impedance issues to worry about; the CD player will have a very low output impedance, and the mixer's line input will be high impedance, so that will just work as intended.
There won't really be a significant level difference issue either, because CDs are generally mastered to within a gnat's whisker of the peak level, which will be around +8dBu from a typical domestic CD player. So it's already a reasonably healthy line level anyway, and there's probably plenty of gain range available on the mixer to match other sources.
As for the balanced aspect, the benefit is an avoidance of ground loops and a rejection of interference, neither of which are likely to be issues in your situation. Most domestic CD players are double-insulated (class 2) devices with no mains safety earth connection. That being the case, there's no risk whatsoever of a ground loop, so running an unbalanced connection isn't going to cause a problem in that respect. And as already discussed, the signal is a pretty comfortable line level anyway, so interference isn't likely to be a problem either.
So, yes, you could do the job 'properly' and invest some money in a proper unbalanced-to-balanced gain-boosting box — and if you were going to put the CD player's output on a patchbay and plug it in to feed who-knows-what-or-where then I'd say that was a sensible approach. But you appear to just want to connect it permanently to a mixer's inputs, so there's really no need and no point in buying a converter box. A simple RCA (phono) to TS plug cable will get the job done just fine. (If the CD player is unusual in being a class-1 device with a mains safety earth connection — very unlikely, but theoretically possible — then you might need to use pseudo-balanced cables instead, to avoid the risk of a ground loop, but that would be very easy to do if you can solder a TRS plug onto a standard unbalanced cable!)