What it does to your sound
As a boost and preamp, the Short Stack sits in the family of boost pedals and preamp pedals that shape gain before or after the rest of the board. Pedal of the Day's reviewer wrote that "the Short Stack beefs up your other pedals and drives your favorite tube amp to the sweet spot with ease," which is the classic role of a booster: pushing overdrive pedals harder or driving a tube amp's input into distortion territory.1
Delicious Audio, in Paolo De Gregorio's product write-up, describes it as "a Preamp/Boost that provides guitarists with a lot of options to reach that fleeting tone they hear in their heads."2
The controls
The pedal has four knobs, and Delicious Audio notes that three of them act as gain stages: "The four knobs already provide three stages of gain (Volume, Level and Gain, which is the internal amp)."2
| Control | What it does |
|---|---|
| Gain | Adjusts the amplifier gain, the internal amp stage1 |
| Volume | Sets the output amount1 |
| Level | One of the three gain-stage knobs2 |
| Bias | Sets the amp's bias; Delicious Audio describes it as fine-tuning the high-end12 |
Half Stack and Full Stack modes
Inside the pedal, two amplifier topologies are available via a PCB-mounted switch, labeled "Half Stack" and "Full Stack." The difference is gain and clipping character: Full Stack injects a pair of matched current sources to create an additional +40dB of gain with softer clipping.12
The mode switch and the other options live under the hood. A set of DIP switches inside the pedal selects full stack or half stack, a linear or nonlinear DC feedback setting, and true or buffered bypass. Changing any of these means opening the pedal, not flipping a top-panel toggle.12
Bypass and power
The Short Stack offers switchable true or JFET-based buffered bypass, selected via a PCB switch, so a player can choose whether the pedal hardwires the signal when off or leaves a JFET buffer in the chain.12 The pedal also includes reverse and over-voltage protection.1
What reviewers said
Pedal of the Day's verdict, from May 2021, was warm: "We love this first creation from Whimsy Machines, and can't wait to check out more from them soon."1
Videos
Whimsy Machines
Demos In The Dark
Brett Kingman
Questions
Is the Whimsy Machines Short Stack true bypass?
It is switchable: a PCB-mounted DIP switch lets you choose between true bypass and a JFET-based buffered bypass. That means you can set the pedal to hardwire the guitar straight through when it is off, or leave a JFET buffer in the line, which some players prefer on long cable runs or larger pedalboards.
What is the difference between Half Stack and Full Stack?
They are two amplifier topologies inside the pedal, selected with a PCB-mounted switch. Full Stack injects a pair of matched current sources to create an additional +40dB of gain with softer clipping, while Half Stack runs without that extra stage. Both are set internally rather than from the top panel.
Can the Short Stack push a tube amp into overdrive?
Yes. Pedal of the Day's review says the Short Stack 'beefs up your other pedals and drives your favorite tube amp to the sweet spot with ease.' As a booster with a lot of gain on tap, it is the kind of pedal players put in front of a tube amp to push the input stage into overdrive.
What does a JFET booster do?
A JFET booster uses a junction field-effect transistor as its amplifying device. The Short Stack is a single-stage, ultra high gain JFET amplifier, and its maker describes its range as running from clean amplification to overdrive and warm distortion. JFET stages are often used to give a preamp-like character to a boost.
Where is the mode switch on the Short Stack?
The Half Stack and Full Stack switch is mounted on the PCB inside the pedal, not on the top panel. You open the pedal up to change between the two amplifier topologies. DIP switches under the hood also handle the linear/nonlinear DC feedback option and the true/buffered bypass choice.
Does the Short Stack have reverse polarity protection?
Yes. Pedal of the Day lists reverse and over-voltage protection among the pedal's features, so a wrongly wired power supply should not damage the circuit.
Sources (2)
- Whimsy Machines Short Stack JFET Booster Preamp, Pedal of the Day (www.pedal-of-the-day.com), 2021-05-17
- Whimsy Machines Short Stack Preamp, Delicious Audio, 2021-07-13