What's the difference between active & passive pickups?

[smoguzbenjamin]

I wanna get this straight for myself. A passive pickup is basically an inductor with a bunch of magnets which pick up the magnetised guitar string's vibrations, therefore generating a tiny bit of voltage, right? But whatabout active pickups? Are they passives with a booster popped in, or is there some mystery circuitry hiding withing the pickup itself? :? I've been trying to figure it out for myself but I can't think of a satisfactory answer.

[toneman]

"active" pickups have a preamp.

most of the time, just a single JFET running off 9V.

The "other" kind, sometimes called "passive", have no preamp.
A guitar pickup consists of a coil of wire with a magnetic pole
piece for each string.

With no string movement, the magnetic field of the magnets
(in the pole pieces) are static.   When the string vibrates,
the magnetic field changes in *exact* proportion to the strings
vibrations.  *This*  is what your amp amplifies.

"tone sucking" is a reference to the effect device "loading" the pickup's
output.   "Loading" alters the "free-air"(no-load) vibratory nature of the string in the magnetic field.(changes frequency response)
Clear?
as glass?  as mud?
staytuned
tone

[smoguzbenjamin]

OK so I was right after all cheers!

[GuitarLord5000]

http://www.till.com/articles/GuitarPreamp/index.html

Check out this DIY preamp circuit.  It seems pretty simple, but I haven't tried it.  According to his website, Paul Marossy has tried it.  He might tell us how it sounds.  How 'bout it Paul?

edit:  For the sake of being honest, I found this preamp circuit through Paul's site here:
http://diyguitarist.com/

[Transmogrifox]

Many times active pickups also are piezo electric, which have such a small output that they DO need an onboard preamp.  Piezo is not magic, it's just a quartz crystal, basically.  With crystal, you apply mechanical pressure (vibrating guitar string), you get a voltage, if you apply a voltage, you get mechanical movement.  That's why crystals are commonly used in oscillators.  So....the guitar string vibrates the crystal, the crystal developes a voltage, and a high-impedance (hopefully very low noise) preamp amplifies the voltage to a line level signal.

Just to clarify, "Active Pickup" refers to either magnetic or piezo being amplified or buffered...so you were right.

[smoguzbenjamin]

Cool :mrgreen: Thanks guys!