The Vibrato, LLC GlassJaw is a high voltage vacuum tube overdrive pedal, described by Pedal of the Day as working great as a boost or as a drive1. It sits in the overdrive camp but with a simple enough control layout that it can be pushed into boost territory just as easily.
How the circuit works
The GlassJaw uses a 12AX7/ECC83 tube internally, and a JFET transistor pre-amp drives the first stage of the tube1. The 12v input voltage generates +150vDC via an internal Buck-Boost power supply, for maximum output power1. That high voltage is what separates it from pedals that run a tube starved of plate voltage: the tube here is running at proper amp-style levels.
The tube's heater and high voltage plate voltages are active as soon as the +12vDC is plugged in, even when the pedal is bypassed. This is deliberate: it prevents any delay in sound output from tube warm-up when you stomp on the pedal. It also means the tube is drawing power whenever a supply is connected, bypassed or not1.
Controls
The control section is minimal. The Output knob controls the audio output, and that is the extent of it1. Pedal of the Day called it a "dead simple control section"1.
What reviewers said
Pedal of the Day described the GlassJaw's tones as warm, sweet-sounding and amp-driving, adding tube warmth, making notes pop and giving chords sustain1. Their verdict on how it fits a board:
"this is the kind of pedal you'll want to leave on all the time"
They summed it up as a real set-it-and-forget-it kind of effect overall1.
Availability
As of the March 2020 review, the GlassJaw was sold via Tindie1.
Videos
Pedal of the Day
Questions
Does the GlassJaw use a real vacuum tube?
Yes. The GlassJaw uses a 12AX7/ECC83 tube internally, with a JFET transistor pre-amp driving the first stage of the tube. The 12v input voltage generates +150vDC via an internal Buck-Boost power supply, so the tube runs at high voltage rather than at starved pedal voltages.
What power supply does the Vibrato LLC GlassJaw need?
The GlassJaw takes a 12v DC input. That 12v input voltage generates +150vDC via an internal Buck-Boost power supply for maximum output power. Because the tube heater and plate voltages are active as soon as the +12vDC is plugged in, a dedicated supply is part of how the pedal is designed to run.
Is the GlassJaw true bypass?
Yes. The GlassJaw uses a true-bypass foot switch. Even so, the tube's heater and high voltage plate voltages stay active when the pedal is bypassed, as long as the +12vDC supply is plugged in, so the tube is already warm when you switch the pedal in.
Is the tube still powered when the GlassJaw is bypassed?
Yes. As soon as the +12vDC is plugged in, the vacuum tube heater and high voltage plate voltages are active, even when the pedal is bypassed. The design keeps the tube warm to prevent any delay in sound output from tube warm-up when you engage the pedal.
Can the GlassJaw be used as a boost?
Yes. Pedal of the Day found that the GlassJaw works great as a boost or as a drive. With a single Output knob controlling the audio output, the control section is simple enough to set as either, depending on how hard you push it.
Sources (1)
- Vibrato LLC GlassJaw Vacuum Tube Overdrive, Pedal of the Day, 2020-03-26