ZBox is small, useful, and works with any guitar or bass that has passive pickups.
Guitar pickup impedance adapter
Standard guitars with passive pickups can’t drive line inputs or mic inputs effectively, so interface manufacturers introduced special “instrument/hi-impedance” inputs to accommodate guitar. These prevent pickup loading, thus preserving level and highfrequency response. (With pickups, loading reduces highs and level because impedance increases with frequency.)
However, many real-world guitar amp inputs do add slight, but noticeable, loading. A tube stage’s input also interacts with guitar. These combine to create what some guitarists call a “warmer” tone although technically, it’s not as “accurate” as a hi-Z input.
ZBox is a simple, passive box with two 1/4" inputs (high and low impedance, relatively speaking), and an attached 18" output cable terminating in a 1/4" unbalanced out. To transform a high-impedance input (whether in an interface, mixer, wireless transmitter, etc.) into one that’s more like a “real” guitar amp, a resistor network provides the necessary loading, while four silicon diodes connected in series provide (very) soft asymmetrical clipping starting at around 2.8V—so it’s just barely shaving the tops of the positive peaks.
With amp sims, despite the best efforts at modeling, feeding in a bright signal—which happens with a high-Z input—can sound brittle. ZBox adds a subtle rollback of the highs and also interacts with the midrange, but the effectiveness depends on several factors.
Using active pickups, or inserting an effect between guitar and ZBox, is pointless; to work its magic, ZBox must insert between the passive guitar out and interface Hi-Z in. Also, rolling back the guitar’s tone or volume control greatly reduces ZBox’s effect. I tested it with a Strat bridge pickup going through the Softube White Room (set for heavy distortion) and Les Paul neck pickup going into the Softube Green Room, then recording both for an online web clip. Listening back, the effect is subtle, but noticeable. The Low-Z input loads the signal down enough so a bit less level feeds the sim, which equals pulling back the drive somewhat. But there’s more to it than that. Using either input— especially with the Les Paul—gave a timbre I’d characterize as “rounder” or “smoother.”
Depending on the pickup, playing style, and amp sim setting, ZBox’s effect ranged from barely noticeable to both significant and useful. This is the kind of box you could hard-wire into the signal path when feeding a sim—it can’t hurt, and more often than not, definitely helps.
Inexpensive. Passive— no power needed. Adds a subtle smoothness to amp sim tone.
The degree to which it improves tone depends on multiple factors (but it never makes the guitar sound worse).
More from this Roundup: