So I tried the Boss OC-3 (my drummer had one):
guitar --> OC3 --direct out--> tuner --> guitar amp
--effect out--> bass amp
In the 'poly' mode the tracking on the Boss is pretty decent, probably not as good as a POG, but workable. It does play polyphonic notes on the output too, however there is an adjustment control which acts as a range - so you can set the highest note to which the octave effect is applied.
I set the range to trigger on the 7th fret on the A string and below - so the 2nd highest E. There is a bit of 'fuzziness' here - you can't set an exact cut off, but you can get it near enough.
Anyway, this obviously triggers power chords on the octave output if you fret them on the E and the A. Thats not ideal, but you can work around it.
I think the tracking could be a little better, it always gets the right notes, but if you are playing *really* fast it is a little sloppy.
All of this stuff you can work around, being careful when playing chords on the lower strings - getting a good set-up on the range control. Also the Boss's octave tone isn't the greatest (sounds like a synth rather than a bass guitar) but its totally fine and has its own charm.
The range control, and the separate direct/effect outputs are what make the Boss probably the only usable for this. I wonder about a POG, but feeding it with filtered signal, split from the main guitar signal - but this is already two extra pedals.
So what of the actual results? There is a small adjustment in playing style as I say, but the results are well worth it! The low end of the octave is **absolutely immense** through the separate bass amp.
If you leave the low E, or A, ringing you can solo on the upper strings and you get a lovely warm drone filling in the bass end.
I've just ebayed my own OC-3 and a little mixer to experiment further at home.
One idea I had was to use a normal guitar pickup but with 12 pole pieces, wired to its own output. If you removed the pole pieces of the 4 upper strings, you could use a better sounding pedal - something like the POG maybe. But anyway, that would involve mods to the guitar. The Boss does it all in one handy box.
A manufacturer could easily make a better version of what the Boss OC-3 does. In poly mode it doesn't really play only root notes, its genuinely polyphonic, but the range knob allows you to work around it. Modern digital technology would definitely allow detection of the root note.
In the absence of something better, the OC-3 is decently workable in this application as a bass emulator. There doesn't seem to be an easier/better solution at the moment.
