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View Full Version : How do Passive Pickups work?



kissing
04-09-2009, 05:40 PM
While I save up for a better purchase from MGM, I got myself a relatively cheap Mahalo soprano with a pickup (http://www.melmusic.com.au/shop/products_pictures/56530.jpg) (which I believe to be passive, since there is nowhere to put in a battery.. it's just a hole on the side).

But I was wondering how I could easily test whether this pickup is actually working, or it's just "for show" (ie: it doesn't work.. but it's just to look like I have a pickup :cool: ).

I tried plugging the pickup to headphones, but couldn't hear anything.
Then I tried plugging in to my speaker system (for computer) and didn't hear anything. I did get a very weak signal when I plugged it into my computer's line-in and recording on Audacity.. but the volume was very low and only for the left (no right).

Do passive pickups only work properly when plugged into a proper mixer/amp system?

psesinkclee
04-09-2009, 05:54 PM
It's probably a passive pickup, since you can't see any battery pack.

Do get sound out of the uke through the jack, you need to run it through an amplifier. Plugging headphones into the jack won't produce a sound, since there isn't an amplifier there.

I'm not too savy with pluggin directly into a computer, but I believe you need some sort of usb/firewire interface to get the track in there.

UkEdman90
04-09-2009, 06:40 PM
passive pickups can be plugged into a computer but you will need some sort of fire wire usb module like already stated which can amplify the passive signal and turn it active then to computer. a passive signal is so little plugging into a computer would produce a terrible sound.

ichadwick
04-10-2009, 02:29 AM
Passive pickups are piezoelectric (http://en.wikipedia.org/wiki/Piezoelectric) pickups. They generate a small electrical charge when compressed and released.

The amount generated is so minute that you need an amp to make it loud enough to hear. Your headphones have no circuitry to translate that pulse into a sound, although you might hear a tiny crackle as you play.

You can find lots of piezo devices that use the same principle. A lot of BBQ starters are piezo - especially the ones built in those backyard units. They work by simply compressing the crystal then suddenly releasing it. That generates a small spark. Basically that's how a passive pickup works - the wave compresses the crystal and then releases it, generating a tiny current. This gets translated into sound by your amp.

If you remove the saddle, you will see a thin sheet of copper foil, then the piezo unit, and below it another copper foil. The foil catches the spark and carries it to the jack and thus down the cable to the amp.

Ukulele JJ
04-10-2009, 02:33 AM
Right. Any time you get sound out of a pickup, you need these two things:


The pickup itself.
A preamp. That is, some sort of powered, electronic device that, among other things, takes that very low-level signal and amplifies it to a level that's more useful.


With an active pickup, you get both parts built into the guitar. So you're good to go... just plug and play.

With a passive pickup, you need to provide that second part--the preamp. You can buy a separate, standalone preamp, and then just plug whatever you'd plug into the guitar into that preamp instead. Basically, it's like taking the part that would be inside an active-pickup guitar and placing it outside the guitar.

Guitar amps have pre-amps built-in, so you can use that too. And many (most?) USB audio interfaces will have a pre-amp in them too, which will help you when recording into your computer.

JJ

kissing
04-10-2009, 04:24 AM
Thanks for the help everyone :)

I could not find this information anywhere else! Thank goodness for UU!