The Whimsy Machines Short Stack is a handmade JFET booster and preamp pedal built around a single-stage, ultra high gain JFET amplifier. Whimsy Machines describes it as a Preamp/Boost that gives guitarists a lot of options for reaching the tone they hear in their heads, and both reviewers who covered it describe its range the same way: clean amplification at one end, overdrive and warm distortion in the middle, and what the maker calls murder-your-face amplification at the top12. If you are shopping this territory, it sits among boost pedals and preamp pedals rather than the overdrive or distortion categories, though its gain range reaches into both.
A JFET preamp with three stages of gain
The heart of the pedal is one JFET amplifier stage run at high gain. Pedal of the Day calls it "a single stage, ultra high gain JFET machine"1, and Delicious Audio's Paolo De Gregorio describes it as offering "clean amplification to overdrive and warm distortion to murder"2. Pedal of the Day's reviewer found that "the Short Stack beefs up your other pedals and drives your favorite tube amp to the sweet spot with ease"1, which is the classic role for a preamp of this kind: pushing an amp's input, or adding gain in front of other pedals on the board.
The pedal is a handmade unit with meticulously designed original circuitry, and Pedal of the Day notes its throwback, nostalgic graphics1.
The knobs and DIP switches
The front panel carries four knobs, and between them they already provide three stages of gain2:
| Control | What it does |
|---|---|
| Volume | Sets the output amount1 |
| Level | Sets the amp input level1 |
| Gain | Adjusts the amplifier gain, the internal amp12 |
| Bias | Sets the amp's bias; per Delicious Audio, there to help fine-tune the high-end12 |
Under the hood, a set of DIP switches adjusts several further options2:
- Half Stack / Full Stack: two amplifier topologies, selected with a PCB-mounted switch12
- Linear / nonlinear DC feedback: a feedback character option listed by Delicious Audio2
- True / buffered bypass: switchable true bypass or a JFET-based buffered bypass, also on a PCB switch12
The Half Stack and Full Stack selection and the bypass choice are both PCB-mounted switches, not panel controls. Changing them means taking the pedal off the board and removing the back plate, so they are set-and-forget options rather than performance switches12.
Half Stack and Full Stack
The internal topology switch is the pedal's biggest tonal decision. In Full Stack mode, a pair of matched current sources is injected into the circuit, creating an additional +40dB of gain with softer clipping12. Half Stack is the other topology, with the lower gain of the two2. For a player, that means the same pedal can be set up as a moderate clean boost or, with the switch flipped and the knobs turned up, as a high-gain preamp pushing an amp or downstream pedals hard.
What reviewers said
Both published reviews date from 2021. Pedal of the Day reviewed the Short Stack on 17 May 2021, covering its controls, the internal Half Stack and Full Stack topologies, and its feedback modes, and classed it as a boost and preamp offering clean amplification through overdrive and distortion1. Delicious Audio's Paolo De Gregorio, in his July 2021 product write-up, framed it as "a Preamp/Boost that provides guitarists with a lot of options to reach that fleeting tone they hear in their heads"2.
Pedal of the Day also notes a connection within the maker's output: the Short Stack is a variant of the dopecrumb, which Whimsy Machines describes as a handmade one-of-a-kind guitar pedal with meticulously designed original circuitry1.
Videos
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Brett Kingman
Questions
Is the Whimsy Machines Short Stack true bypass?
Yes, and it is switchable. The pedal offers true bypass or a JFET-based buffered bypass, selected with a PCB-mounted switch. Delicious Audio lists this as true/buffered bypass, and Pedal of the Day describes it as switchable true or JFET-based buffered bypass via a PCB switch, so a player can choose between the two on their own board.
What does the Bias knob do on the Short Stack?
The Bias knob sets the amp's bias, according to Pedal of the Day. Delicious Audio describes it as a control there to help fine-tune the high-end. In practice it is the knob for dialing in the top of the sound once the gain stages are set where you want them.
How much extra gain does Full Stack mode add?
Full Stack mode injects a pair of matched current sources, creating an additional +40dB of gain with softer clipping. That figure comes from both Delicious Audio and Pedal of the Day, who describe the mode as one of two amplifier topologies selected with a PCB-mounted switch, the other being Half Stack.
Is the Short Stack a boost or an overdrive?
It is both, depending on where you set it. It is a single-stage ultra high gain JFET booster/preamp, and both reviewers describe its range as running from clean amplification to overdrive, and from warm distortion to what the maker calls murder-your-face amplification. Pedal of the Day classifies it as a boost and preamp.
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
