I hope this is the right place/forum to ask this and with apologies if this has already been covered. I saw a few posts about PA's as bass amps but I did not see this specifically addressed:
If one was to plug into a PA to use as an amp, do you *have* to use a pre-amp pedal or DI in front of it or can you just plug in and play?
Thanks gang.
You don't
have to use a DI to plug direct into most modern boards, but it's a good idea. Similarly, a preamp at your feet or in the backline isn't a hard requirement, but it can do good things for you.
The point of a DI is to reduce the portion of the signal cable that is high-impedance and unbalanced. The former gives you the infamous "tone suck" through capacitive loss as cable length increases, while the unbalanced signal line is prone to pick up noise. XLR cables can be dozens or hundreds of feet long without causing these problems (at least not to anywhere near the same degree) because the circuit they are used in is specifically engineered to solve them, thus allowing the soundman to be out in "front of house" using his own ears and his own fingers to mix based on what the audience is hearing, instead of having the board backstage and having to be content with using an assistant either to give mixing cues or have their fingers on the faders.
Now, if the band is mixing themselves (been there, done that, can't recommend it but sometimes you just gotta get 'er done), or if you're using a powered PA speaker cab as a bass amp (been there, done that too, it's actually not a terrible idea) then you probably don't have a 300-foot stage snake between your bass and the input; your 20-foot cable could very easily reach to a board one side of the drumkit or behind the curtain on your side. Most modern mixers can handle an unbalanced signal without breaking a sweat (the connections involved mean you're just "wasting" the cold conductor), and at least a few are specifically engineered for Hi-Z inputs. Likewise, most powered PA cabs will take an unbalanced 1/4" in with no problem.
The X-factor is going to be your tone-shaping ability, both in general and what you yourself can control. That's where a preamp comes into play. The channel strip of the mixer can be a preamp, and most powered speakers have some rudimentary tone-shaping, however these are usually geared toward tweaking the source to sit in the mix or to avoid feedback. Anything you want to do to start with "your" tone, including EQ, is going to require tools in the signal chain between bass and PA.
Now, we can debate who really
should have the most control over your EQ; I've played gigs with soundmen that didn't have a clue how to do anything but bump faders, leaving me to my own devices on EQ to avoid causing earthquakes or clashing with the guitars. I've also run sound for instrumentalists that insisted on keeping their V-shaped bedroom scoop, that I had no prayer of undoing at the board to give the audience anything like a balanced and audible mix of the band. Neither is ideal; the ideal scenario is a player who knows how to get his instrument to naturally sit in the overall stage mix, and a soundman who knows his system well enough to tweak that mix to fit the venue. But, we live in the real world, and reality is rarely ideal.
In summary, what you need on-stage depends on the overall setup. By using the PA, you're making the PA part of The Complete Instrument™. The difference is going to be that this major element of the sound you hear on stage, in turn determining your ability to play in time, in tune and dynamically with your group, is no longer under your direct control (unless you're using PA components as your stage rig separate from the house PA). For most knowledgeable, competent players, having at least some control over what the soundman gets is a good thing.
) patched in for when you want to use that.
