Adapted from the book Guitar Effects Pedals: The Practical Handbook (Backbeat Books)In the previous installment of
this series we discussed three of the more prominent effects in the modulation camp—
phasing, flanging, and chorus—so this week we’re dropping in on vibrato, tremolo, the octave divider, and the ring modulator. They take us back to some of the earliest effects of the 1950s and 1960s, and even before. And while some of these effects seemed almost forgotten for a while, many of them have been rediscovered in recent years for the powerful and evocative tone tools they really are.
Vibrato & TremoloThese are the old boys of effects. They shake things up, and lend a little wobble to the groove—and for that, we love ’em.
VibratoTrue vibrato, as distinct from the volume-chopping tremolo effect often mislabeled as such, is an actual wavering of the note above and below pitch to create a sort of harmonious “wobbling” effect. Singers do it, and guitarists do it when they wiggle a finger against string and fingerboard or tremble the arm of a vibrato tailpiece. Heavy true vibrato can get a little seasickening, just like heavy digital chorus or flanging, as described above, but good implementations of the effect are usually subtle, and can add a gently beautiful movement to a guitar part.
Electronic vibrato was achieved early on with a relatively complex circuit that usually required at least two preamp tubes. It was most often installed in amps but occasionally built as a stand-alone box, as with Gibson’s GA-V1 Vibrato Box.
Fender, guilty of mislabeling many amps with a “vibrato” channel although they only carried opto-controlled tremolo (while simultaneously calling its guitars’ vibrato tailpieces “tremolo units”), did build a few of its first front-control-mounted brown and blonde Tolex amps of the very early 1960s with a subtle form of true vibrato. (Despite its name, the earlier tweed Vibrolux carried tremolo, produced by a circuit similar to that used in the slightly larger Tremolux.) As it appeared on the 6G8 Twin and 6G5-A Pro Amp of 1960-61, the vibrato effect required two and a half 12AX7s of the preamp’s total of five, excluding the phase inverter (the vibrato circuit “wasted” half a tube, which was left unused). It also required about as much circuitry again as the rest of what was used for the two channels combined, and was clearly a lot of work to build. It sounds fantastic, too, although it’s still just barely “true” vibrato—a subtle example at best. But it just wasn’t worth the effort, apparently, and was dropped after just over a year of production. Gibson, Vox, Magnatone, and a few others also offered amps with true vibrato.
The effect is achieved today in solid state guitar pedals with circuits similar to those used for analog chorus units, or sometimes in high-end pedals with fairly complex discrete transistorized designs that are modified variations on early phasers. A few companies, notably boutique amp builders
Matchless and
Victoria, have also offered tube-powered units that work along the lines of the shortlived Fender vibrato circuit. When done right, it’s a lush, moody effect that adds thickness and motion to any guitar part in a manner shared by all of the better analog modulation effects.
TremoloAs we intend the category, tremolo might not seem like modulation; strictly speaking, however, you could argue its inclusion because, in the literal sense, the effect rapidly modulates a signal from the on state to the off state (or nearly off). Really I’m just sticking it here because I don’t feel like creating a one-pedal category to hang tremolo out on its own—or maybe alongside volume pedals, which hardly even seem worth discussing. Not that I, and many others, don’t feel it deserves a genre all to itself. We love tremolo, and as simple as it is, when used right it can still be one of the most haunting effects out there.
Tremolo first appeared in the form of a number of add-on units (often too large to be called “pedals”), and in fact the first stand-alone effect of all time was a tremolo unit made by DeArmond, the Model 800 Trem Trol (at left). By the mid 1950s the effect was included on amps by Gibson, Premier, Danelectro, and eventually Fender. Early amp-based tremolo circuits usually either acted between the phase inverter and power tubes to cut the signal as it entered the output stage of the amp, or tapped the bias circuit to pulsate the 6V6’s on and off, and as such this can’t be replicated in a pedal. On the other hand, the opto-cell circuits used in many amps from the ’60s on, with their atmospheric-sounding lopsided triangular waveform, can be adapted to fit into a pretty small box. These circuits are based around a photo-coupler made from a small neon lamp and a
light-dependent resistor (LDR) coupled together in a small, opaque tube. An oscillator makes the lamp pulse at a speed determined by the effect’s “speed” or “rate” control, and the LDR injects this pulse into the guitar signal with an intensity determined by the “depth” control. While most amps of the 1960s and ’70s that carried this effect used a tube to drive the oscillator, most pedals that use a photo-coupler convert the drive section to a transistorized stage.
Most budget to mid-priced pedals, however, do things even more simply. As with the majority of pedals, they use ICs to accomplish all oscillation and modulation tasks, usually with transistorized input and output stage buffers. While purists will argue vehemently for the tonal purity of discrete transistorized circuitry in most applications (that is, without
opamps or ICs of any sort), it is probably harder to make the case that a basic dual opamp-based tremolo pedal that effectively pulsates your volume on and off is dramatically inferior to a discrete opto circuit. Still, use your ears and decide for yourself.
Tremolo dropped from fashion in the late 1970s, through the ’80s and into the ’90s (aside from its use at the hands of a few cool guitarists who always knew what it could do). At the time, it just sounded old fashioned up against long digital delays, digital chorus and flanging and all the rest of it. As with so many sonic colors from the early days of rock and roll, however, the effect has built a major new following (
the Twin Peaks soundtrack from the early 1990s probably reminded a lot of people of its haunting power). Many, many great guitarists now keep a tremolo pedal on their board, or play through an amp with onboard tremolo, and many will argue vehemently over the merits of different designs.
Octave Divider 
This is a relatively simple effect, but also one of the freakiest when used right or, sometimes more so, when used wrong. Like a surprising number of classic sounds, this first came to us via Jimi Hendrix, from a custom-built Roger Mayer Octavia—famously heard on “Purple Haze,” and plenty of
other Hendrix tracks besides. Mayer developed an octave divider with fuzz for Hendrix out of his own experiments with doubling the frequency of a signal in order to make it appear to add a note an octave up from the original, but never offered the original unit as a commercial item. This left the door open for
Tycobrahe to offer its own Octavia copy, and that unit was followed by clones from a host of others.
The circuit itself is fairly simple: three transistors, a couple of diodes, and an impedance interstage transformer, along with the usual caps and resistors. Primitive stuff, but it has a wild effect on a guitar signal. As Mayer himself put it to me, “It doubles the number of images of the note. And that, apparently, makes it sound twice the frequency—whereas it really isn’t. Because the signal’s going up and down twice as much, even though you’ve changed the relationship of it, the ear perceives it as twice the frequency. Though it isn’t. It’s much like putting a beer mat up to a mirror and you see two of them, but there’s still only one.” (Uh, the conversation was in a pub in West London, hence the beer mat analogy). So, a simple circuit, but a complex aural trick.
Octave effects are among the trickier pedals to use well, because the circuit only tracks well if a single, pure, cleanly played note is introduced—and honks into total freak-out if it sees an interval. Also, the fewer harmonics the better, so firm picking on a neck pickup does it the most favors. Again, Hendrix’s own playing provides a good lesson in how to use an octave fuzz, and you can usually hear how he cleans up his technique—simplifying the blues slurs, trills, and bends that are otherwise plentiful—in order to make the most of the effect. The octave divider’s prevalence in heavy rock of the late 1960s and early ’70s has left it a somewhat dated effect—and a genre-tied sound, too (you don’t hear it a lot in country)—but a few adventurous players continue to apply it creatively to adventurous modern music.
Ring Modulators These units come to us from the world of analog synthesizers, and have far more applications there, but can be useful for the guitarist who needs some wild, whacked-out, totally a-guitaral sonic obliteration every so often. Think in terms of the octave divider’s percussive, synthesized octave-up sound, but with more jagged, atonal, random-interval performance. This is another of those tools the flailing guitarist took up in the early 1980s to fight the synth players when electronica promised to take over the world and everyone forgot about “tone” for a few years. For a time it looked as if we had lost the battle, but I’d like to think we won the war.
The ring modulator takes its name from the simplest of its transistorized topologies, consisting of a ring of four diodes and two transformers. Most are somewhat more complex than this. In any case, a ring modulator takes the signals from two sources—either from two separate inputs, or one input and one internal oscillator (called a “carrier frequency”)—and multiplies them to produce a new signal that is totally different from either of the two source signals. The result is a little like an octave divider trying to handle two notes at a time rather than the single, pure note that it’s able to deal with, and coughing up a dissonant mess as a result. The ring modulator is designed specifically to cope with these two different signals, but their multiplication produces a new signal with notes at both the sum and difference of the frequencies of the two source signals. Consequently, this output is a mathematical result with no harmonic relationship to the original notes.
Sounds like a mess, perhaps, and it is—except that most units designed for guitar (or other tonal instruments) generally tap off a portion of the main signal at its input and feed it forward to the output to retain a degree of the original note. This blend of the original guitar signal and the sum-and-difference signal produced by the ring modulation circuit is percussive, jagged, dissonant … and sometimes very effective. Early and basic ring modulators for guitar generally have a single input and generate their carrier frequency internally, occasionally with user-selectable variations. Some more elaborate models—such as Lovetone’s Ring Stinger or
Frantone’s Glacier—allow for internal oscillation selections and add an extra input for using an external control signal, such as a mike, drum machine, separate line level source, or whatever. What does the sum and difference of your own funk guitar riff multiplied with a garage drum loop sound like? Chaotic, probably, but possibly like a major hit, too.
Next installment: reverb, echo, and delay.
Want more Effects Explained?
• Effects Explained: Overdrive
• Effects Explained: Overdrive, Distortion, and Fuzz
• Effects Explained: Booster and Compressor
• Effects Explained: Modulation—Phasing, Flanging, and Chorus