Originally Posted by Jeff Scott
Some are low impedance outs, such as on Wal basses and the Rickenbacker 4002. Certain Alembic models use a 5 pin XLR connector to feed the bass power from an outboard power supply and to send a stereo signal out from the bass.
Personally, I like the Alembic idea of a 5 pin XLR. The reasons for it are simple. It lets you power the bass through the cord. This is not only important to eliminate battery hassles and expense but also to allow you to use higher quality electronics in the bass (similar to what is in your amp) that takes more power than a battery can handle with decent life.
A second reason is it can give you stereo outputs. I've got no basses like that but I do have a couple of guitars with Piezo on one channel and magnetic on the other. I REALLY like that effect sometimes with two amps and separated cabs.
A third reason is the output can be balanced which (like microphones) cancels hum and noise eliminating a lot of those problems.
The fourth reason is that that output is low impedance (again like a mic) which means you can put 100 ft of cable on it and not effect the tone.
The fifth reason is that in matching a mic-style output you can go direct to the board without any DI. The BASS is the DI.
Now to comment I'd like to say that I wouldn't want a bass with only a mic level XLR output. The reason would be that mic levels are LOW and you are simply throw noise floor away by padding it down.
But there's a catch. NOBODY who builds amps accepts any such wiring! It is TOTALLY non-standard and even non-standard as far as mics and boards go (5 pin). So you could go 3 pin and mic compatible or 5 pin and have an adapter power supply box (which is what I believe Alembic does).
Personally, I use a different scheme. I use TRS cables for mono with the extra wire (ring) for bass power. I rewire my amp inputs for TRS with a power supply (on an on-off switch). That solves a couple of the above problems. You can run power-hog electronics and even a bunch of LEDs which are cool.
Another scheme that works is the 3 pin thing. I've done this in the past.
I had an old Kingston bass. The pickup died. In those days I was poor and had no idea how to get a pickup for a Kingston anyway. So I rooted through my wire stock and rewound the pickup with finest wire I could find. Which it turns out wasn't nearly fine enough. The pickup ended up with about 100 Ohms impedance! Not giving up, I grabbed a mic to line transformer and discovered it worked GREAT! It stepped up that low impedance and best of all with low inductance in the pickup it had a very wide flat clear response!
Well, being a noob, I ended up doing the wrong thing. The right thing would have been to put the transformer AT THE AMP to take advantage of the low Z driving a long cord. But no, I put the transformer at the bass so it would drive a standard amp like it used to. There was some tone advantage but basically the same "tone suck" of long cords persisted. I still have that bass! But nevertheless it was a very interesting and educational exercise.
If I did that now I think I'd go with XLR 3 pin out with a Mic /line level pad switch and do the direct to board or to a mic-line transformer at the amp. One problem these days is that quality mic-line transformers are much harder to find and really expensive when you do find them.