Active Pick-ups

[Emanuel Apascaritei]

Hi, I´d like to know what is the difference between an active pick up and a passive one - construction, tone, good things and bad things about them.

Note: I´m not refereing to active basses that have an active preamp and the pick-ups are still passive.

Thank you!

 

[Stealth]

A passive pickup is a high-impedance coil wound with a relatively high number of turns - commonly over 5000 turns on a single coil. Part of the high impedance is the high resistance - these coils are typically between 5kΩ and 12kΩ (with the "fattest" pickups being in the 30kΩ range - the Gibson sidewinders, for instance).

An active pickup is a low-impedance coil wound with a small turn count - commonly under 2500. The resistance of these pickups is usually fairly low, on the order of 1 kΩ. In order to bring the pickup output to a level similar to that of passive pickups, active pickups have a built-in preamplifier that runs on a 9V battery - and this one actually works as an amplifier, not just an active set of controls.

The good thing about active pickups is that the low turn count means less hum picked up, and, if made with a good preamp, even single-coils are commonly quieter. However, the downside is that active pick-ups simply do not work without the battery (the output is negligible), whereas with a passive bass with active circuitry you can always bypass the circuitry and go fully passive if the battery goes flat.

As far as tone goes - I wouldn't hazard to guess. All my basses have passive pickups - of those, two have active electronics, but as you've already said yourself, it's not the same.

 

[JTE]

The main points of active PUPs are controlling signal loss and shaping sound. Ron Wickersham from Alembic has reported that while they were experimenting with Jack Casaday's Guild Starfire's pickups (made by Hagstrom), they found that there was noticable high-frequency loss with even three inches of cable between the PUP and the first stage of amplification. So they decided to put the first amp stage right in the pickup.

From there active PUPs have developed. You can make a pickup by optimizing the sound without regard to output. Everything's a trade-off. More turns gives you more output, but you change the sound. So and active PUP like an EMG can be wound to give the sound the designer is after, and use the pre-amp to boost it up to a level that works with the amp. NOTE: That doesn't mean active is necassarily higher output than passive, and often they are NOT hotter.

They can also be designed so that you can make a fully humbucking pickup and shape the sound coming out of it to sound like a single-coil. That has as much or more to do with active PUPs being noiseless than the impedance. But the impedance factor also allows active systems to drive longer cable runs without high-frequency loss, which is where Alembic started from.

Pros and cons are pretty subjective. Yeah, the require a batter, but most have such small current draw that the whole battery thing is a red herring. For most players, changing the battery once every year (or six months, or whatever) isn't going to cost them a gig.

They sound different. I've never heard an active PUP that nails the sound of a good passive Jazz bass sound. But then, I've played quite a few that work well to emulate a Jazz bass enough that it could be exactly right for you. My favorite P/J combination is EMG's BTW. They just work really well together, which doesn't always happen with passive P/J PUPs.

John

 

[Emanuel Apascaritei]

Great info here, thanks to you all. I was thinking of moding a P-bass copy (do it your self cheap kit) and put some EMG active PUP´s. What do you think about this??