What’s the real difference between active and passive basses, guitars and other stringed instruments? Ever wondered? Well, we are going to check into it now. We will also evaluate them and claim which one is better, so you can bash people that are being fans of the worse technology freely. Just kidding. This is certainly not a life threatening topic. Or is it?
Guitar, bass and pickups
Let’s start with a passive system: it consists of a high impedance pickup, some passive circuitry with volume and tone controls, a cable, and finally the amp (or an effect/preamp). That fact is about the most important thing when you are comparing active circuits to passive systems. If you look at the above signal chain, it’s fully passive up to at least the very end of the cable. By passive, we always mean there is no amplification happening to the signal.
An active instrument system is different: it starts with the pickup(s) that can be either low or high impedance, then you have three options. In case you have an active pickup, it’s got a preamp built directly into it. In the case of an older active pickup system, you can then simply wire a passive tone and volume circuit to it, like in the case of the passive system. You only need to change the potentiometer values. This option was actually a compromise Rob Turner of EMG made early on, so people could still use simple 25kOhm passive pots, and weren’t forced to install a whole different active tone circuit into their guitars as well, on top of the battery. The compromise came from having to have some output impedance, so the preamp in the pickup could “see” the load of the passive controls. This compromise was later overcome by the EMG X series, that use active tone controls, which is our second option, as far as active systems go.
The preamp that got away
The third option is to have a low or high impedance pickup, then have a separate preamp connected to it, with its own tone and volume controls. In either cases, you can easily spot the difference between the passive and the active systems: it’s where the first amplification device appears in the signal chain. In all of the active systems, it’s before the cable. That’s the key difference that makes your active basses or guitars sound way different; have a much more open high end (and actually low end as well). The reason for the tonal difference is that in the case of a passive instrument, the capacitance of the cable loads down the pickup and also sets up a resonant filter. It results in two important things: a resonant peak, that usually falls somewhere in the midrange of the frequency spectrum (about 1000 – 5000Hz), and the treble loss. The problem with it is, the longer your cable is, the lower the resonance. Of course you can always use the same length cable with the same capacitance, and/or try to set it up the same way with a wireless system, but yeah… it’s not the most elegant way, as far as consistence goes. That’s actually the reason why people who claim that plugging a passive bass (or guitar) into a preamp turns it into an active system are wrong. It’s simply not true, because the cable is before the first preamp stage. While you might be able to get similar tones that way, technically it will still be different from an active instrument, and your cable length will always come into play.
Those purists again
When the passive vs active debate comes up, people of the passive fan group will also say they don’t dumb down their sound with preamps. At least not ones built out of cheap parts running on a 9V battery. Well, a guitar circuit is really not that demanding with its low current and low voltages. As far as the value tolerances are okay, you’re good to go, and it’s hard to find a less noisy power supply than a battery. So actives are really good and sweet, except that damn resonance. Which might be enough for a musician to make the decision and go the passive route. Because our ears and brain are very sensitive in the midrange, that resonant peak really becomes the personality of a bass or guitar, the thing that makes it sound ever so sweet to our ears. Of course just about as many people like the hi-fi, wide range sound of the active stuff, as well as the greater tonal control it comes with. Also, some of the resonance can be achieved in the preamp itself, though it will always sound somewhat different from a true passive circuit.
As you can see, when it comes to music, personal preference is usually the main deciding factor.