The Sushi Box FX Underground Accelerator is a tube preamp pedal, part of the maker's range of preamp pedals. Sushi Box FX says it takes inspiration from legendary studio tube preamps, with tweaks to make it more flexible. The maker describes it as having a moderate amount of gain, so it can overdrive when the gain is turned up, or deliver a fat clean or gritty clean depending on the setting. RockBoard's PedalPedia adds that it works as a clean boost or mild overdrive on guitar, and that bass is where it really sings, providing rich bottom end1.
The standard Underground Accelerator is listed as Archived on the maker's product page. The Underground Accelerator Handwired Special Edition is in production3.
Sound and controls
The pedal carries a 3-band EQ, and the newest version adds an EQ bypass switch. Sushi Box FX says the switch removes the EQ from the circuit and affords an extra +30dB of gain2. RockBoard's PedalPedia explains the reasoning: passive EQs like the one used in the Underground Accelerator are inherently lossy, so the bypass was added for players who want the extra gain, which it puts at approximately +30dB1.
The pedal comes in a compact enclosure measuring 4.8 in x 2.64 in x 1.58 in (122 mm x 67 mm x 39.6 mm)2. Sushi Box FX has also published a demo from Jake Serek of Serek Basses2.
Power requirements
Because the pedal runs a tube, its power needs are well above a typical overdrive pedals or boost pedals draw. Sushi Box FX states it plainly23:
"As a tube pedal, Underground Accelerator requires a high amount of current to operate correctly."
The maker recommends a 9-12VDC power supply capable of delivering at least 400mA, and warns that using less than this can damage the power supply and/or the pedal2. That rules out most daisy-chain setups and battery power.
Summer 2024 revised edition
The Summer 2024 revised edition keeps the same circuit as before but adds upgrades, including film capacitors in the audio path and soft-touch relay bypass switching2.
Handwired Special Edition
The Handwired Special Edition is a special edition of the Underground Accelerator. Sushi Box FX describes it as the best version of the circuit the maker could make, quoting the intent as "the best version of this pedal I could possibly make"3. It is an individually serialized, limited run, and differs from the standard pedal in its construction:
- Laser-cut wood faceplate inset into the chassis3
- Robust ceramic tube socket3
- Soft-switched relay bypass3
Its power requirements are also spelled out more precisely: third-party supplies can be used as long as they are center-negative, 9VDC at 600mA or more, or 12VDC at 500mA or more3.
Demo
Sushi Box FX points players to a demo from Jake Serek of Serek Basses on the product page2.
Videos
Serek Basses
Michael Shapinko
Alberto Barrero
Questions
Is the Sushi Box FX Underground Accelerator a real tube pedal?
Yes. Sushi Box FX describes the Underground Accelerator as a tube pedal, and the maker notes that as a tube pedal it requires a high amount of current to operate correctly. The Handwired Special Edition adds a robust ceramic tube socket. Because of the tube, the maker recommends a 9-12VDC supply capable of delivering at least 400mA, and warns that using less can damage the power supply or the pedal.
What does the EQ bypass switch do on the Underground Accelerator?
The EQ bypass switch removes the EQ from the circuit and adds an extra +30dB of gain, according to Sushi Box FX. RockBoard's PedalPedia explains that the passive EQ used in the pedal is inherently lossy, so the bypass was added for players who want the extra gain. The newest version of the pedal carries this switch.
Does the Underground Accelerator have true bypass?
The Summer 2024 revised edition uses soft-touch relay bypass switching, per the maker's product page. The Handwired Special Edition uses soft-switched relay bypass. Neither page describes the switching as true bypass in the mechanical sense; both use relay-based switching.
Is the Underground Accelerator still in production?
The standard Underground Accelerator is listed as Archived on the Sushi Box FX product page as of October 2026. The standard pedal was last revised in Summer 2024 with film capacitors in the audio path and soft-touch relay bypass switching.
Sources (3)
- Undeground Accelerator by sushiboxfx, RockBoard PedalPedia, 2026
- Underground Accelerator, Sushi Box FX
- Underground Accelerator, Sushi Box FX
