Onboard Electronics Basics for Bass Guitar and Guitar: Active Electronics

Courtesy of Rock House Method

By: Dean Wagner

For such a widely recognized term, “onboard active electronics” is more commonly misunderstood than most Primus lyrics. There are many different definitions, but each has one thing in common: Unlike passive electronics, active systems require power, usually in the form of one or more 9-volt batteries.

Your bass’s pickups sense string vibration passively, but amplifying your sound requires external power. Passive electronics often incorporate controls that cut volume and high frequencies, leaving your amp to take care of volume and EQ boosts. Well-designed passive electronics work very well, but they have limited tone-shaping ability and can result in fidelity loss over long cable lengths. Active electronics, usually in the form of an onboard preamp with boost/cut EQ, address these issues and do some volume boosting of their own.

One of active electronics’ most important functions is to transform the pickup’s high-impedance output into a low-impedance signal more suitable for amplifier inputs. It’s important that your bass’s output impedance (the resistance to alternating current) be significantly lower than your amp’s input impedance. If the output impedance is higher than the input impedance, low frequencies can roll off, resulting in a thin sound. Also, low output impedance helps your bass’s signal retain fidelity as it travels down a length of cable.

Active electronics can provide a higher output level and bigger dynamic range than passive systems, but they are limited by the preamp circuit’s headroom. As an active circuit runs out of power to reproduce your sound, dynamic compression and clipping (distortion) can take place, resulting in an unpleasant tone. Most high-quality active circuits are designed for maximum headroom, but it is possible to overdrive an onboard circuit, particularly when boosting the onboard EQ. In contrast, it is impossible for a bass’s pickups to overload a passive circuit.

Active electronics’ EQ allows you to boost specific areas of the frequency spectrum. Many contemporary active systems have 3-band EQ circuits (bass, mid, and treble). Some systems even feature user-selectable boost/cut frequency points or bandwidths. Many proponents of active electronics believe onboard EQ leaves you better equipped to deal with the peculiarities of different playing environments. When abused, though, onboard EQ can overdrive your amp’s input stage or strain your speakers. Remember, EQ is like sonic seasoning, so use it judiciously— extreme settings are rarely necessary.

As with passive electronics, active systems have numerous advantages and disadvantages. Some experts argue that they are less susceptible to noise-producing interference, while others say their more complex design is inherently noisy. One side says there’s potential for sonic trouble, while the other espouses flexibility.