I used a Boss TU-2 for years on a standard EADG bass with no trouble, even when tuned down as far as BEAD. I had bought the thing used from a friend. It looked like hell and had actually been left in the road overnight after falling out of the back of a truck. That was before the 10 years of use with me. I gave it to a friend a few years back and replaced it with a Boss TU-3, using it for a 5 string BEADG. No trouble picking up open strings in either strobe or standard mode. The TU-3 has a bright LED mode and a few other features that the trusty ole TU-2 did not. I'm guessing there's something going on with the pedal or the bass. I've never heard of any such trouble on a TU-2. Of note, my opinion and evaluation are anecdotal.
