| The "active" input usually has a 10bd pad on it. This WILL reduce your ultra high freqs. slightly. Some amps have a single input and a "pad" button. It's the same thing.
I hate 'em and have never used one.
Lets assume you have an amp with a gain AND a master control. (If not everything I'm about to say will not have as drastic effect and some will not even apply.)
Regardless of you basses be active or passive, plug into passive and play has hard as your going to play. Rip into it. Set the gain so that the clip light flashes occasionally. If it's clipping and the gain is still really low, well below 12 oclock, switch to the active input and reset using the same method.
This will assure you're driving the preamp at it optimum operating voltage without unwanted distortion. Basically, all those really cool specs in the manual like THD etc., you just set the pre to do that.
The Master knob will control the over all listening level. If you set up like above you will not have to turn this up much to get a lot of volume. In fact, you'll be surprised how much volume you'll be able to get out of your amp with out hurting anything. You'll also be surprised how responsive the EQ will become. (Expect the need to adjust this. Start from flat.)
(note: if you use a lot of your basses active EQ you'll clip the preamp a lot faster than if you set it flat. More on this below.)
In sound renforcement terms, you set your amp up like a channel strip.
This is exactly how I've ran my rigs for 23 years. Most of it with bands you've heard of. If you see me in a store, I'll do the exact same thing.
Lets say that you've set up this way but you have this one situation where you can't get the amp QUITE enough. turn down the gain and readjust the master. You'll be sacrficing some of your pres responsiveness, but in this situation it's necessary.
(Tip: If you have an active bass, set it's EQ flat. I know, most people turn their bass and treble knobs all the way up but this causes a couple of issues. First, it increases your noise floor I.E. system hiss. What you hear when the amps on but no music playing. Secondly, you clip the amp prematurely which is why most people have to use the "Active" input in the first place.
Although I have active/passive basses, I set the preamp to "on" BUT flat. No boost or cut. I do this for impedance reasons that I won't bore you with here. Also if I have to switch to passive I don't have a volume change.
I let my EQ in the amp do all the heavy lifting as far as tone shaping. [I turn up to freqs. on the low end just to beef up the "B" and "E" strings. other than that I'm flat. this works on pretty much any bass. Active or passive. I've only found 1 or 2 brands of basses this didn't work on.]
This makes for a far more consistent tone regardless of actual playing volume as long as you turn the master volume control only. As a side benefit, your pedals will function and sound better because you're not hitting them with this huge signal. This is especially true for anything that's input sensitive like drives, envelopes, compressors etc.)
I know in about 2 min. someone's going to say I'm full of crap. And then give you 15 reasons why they are smarter. That's fine. i really don't care, but if you try it you'll benefit. It's not my tone. | 
