The signal produced by any pickup source, whether it is an on-board mic, magnetic pickup, or piezoelectric pickup, is just the first link in the signal chain. Before it reaches the audience’s ear it most likely will be run through a pre-amp, direct box, another pre-amp, a power amp and, finally, speakers…not to mention the tens, if not hundreds, of feet of cables that connect them all together.
Some pickup systems are “active” and others are “passive”. Passive systems leave modification of the signal to outboard gear, where active systems contained in the guitar affects the signal before it even makes it to the output jack.
Passive systems don’t require any power, but active systems do. Generally, passive systems don’t have any controls for volume or tone, though there are exceptions. Both active and passive cables with volume and tone controls have been manufactured to give the roving guitarist using such a system close access to controlling their sound.
Active systems have a preamp that requires power, usually in the form of a 9 volt battery, thought there are systems that use AA batteries or disc-type batteries used in watches and other small flat electronic devices.
The battery or batteries are usually contained in the pre-amp when they are mounted on the rim of guitar. If the guitar has a more visually-discreet pre-amp that is mounted somewhere inside the guitar, the battery is accessed through the soundhole. It may be mounted to a clip or secured by some other way to the neck block, the inside back or side of the guitar, or suspended inside from the combination endpin/output jack/pre-amp. Some active magnetic pickups hold the batteries, while others use the previous mentioned methods.
For the most part, power from the battery is only being drained while the guitar is plugged thanks to a switch built into the endpin/output jack. Some, however, have a micro switch that must be manually turned on and off: an often forgotten task that has caused frustration and panic to the owners.
It should be noted that there are some guitar mounted pre-amps that don’t contain batteries. These require phantom power from some other source such as a direct box or pre-amp. For the guitar to receive the power, a cable that has three or more connections to it, such as a mini XLR, a TRS 1/4” plug or other DIN connection is used. These more specialized systems are by far the minority of electro-acoustic guitars.
While passive systems’ volume controls can only reduce the amount of signal (which also alters the tone), active systems boost the signal as the volume is increase while keeping the signal tonally un-altered…unless the guitarist altered it themselves.
In the early development of active systems a tone control was added. And as transistors and large clunky knobs gave way to IC microchips and slim streamline sliders, separate bass and treble controls gave way to parametric EQ’s, feedback busters, digital tuners and onboard effects.
Having access to so much control is considered a boon to many plug n’ play guitarists and singer/songwriters. Tone connoisseurs (and many soundmen) believe that signal altering is best left to the mixing board. Still, it’s nice having the ability to take out a little treble without having to rely on the soundman.
Many guitarists who don’t want to alter the looks or de-value their vintage or boutique instruments opt to use a pickup or combination of pickups (i.e. piezo and mic) with a preamp that is hidden inside the guitar with a thumb-wheel volume control (and a mix control if a combo system is being used) that is discreetly hidden but still accessible just inside the soundhole.
Many systems using two pickup sources use stereo outputs. Using a mono cable the signal of one pickup (usually the most feedback resistant) or a mix of the two is used. With the use of a stereo cable, the signal of each pickup is sent to a different output, allowing each to be dialed in separately and then mixed at the board in either stereo or mono.
One of the newest developments for onboard preamps is the inclusion of digital modeling or imaging. Simply put, the signal from the pickup is digitally enhanced or altered to resemble that of a mic’d or sampled acoustic guitar.
Of course, many outboard preamps give the guitarist the same ability to con
trol their sound before it reaches the mixing board or amplifier. The benefit of using a high-end top-notch outboard preamp is obvious: it can be used with all your pickup equipped guitars.
Jake Kelly is a man on the constant search for enlightenment, if anyone finds it let him know so he can get some. For more of this hombre’s ramblings and the rest of L2P check out L2Pbandspace and L2Pnet.com.
Originally posted 2011-02-22 22:07:11.