The Master Effects Thespian Valve Preamp is a tube preamp pedal for guitar and bass, built around a 12AU7 preamp tube running at 200V plate voltage. Master Effects describes it as a recreation of the preamp found in the Fender Dual Showman and the Alembic F-2B valve preamps, two circuits with a long history among players who want a clean, punchy tube front end. According to the maker, it adds punch, clarity, and dynamics to your tone, and it can work three ways: as an always-on shaper of your fundamental tone, as an extra gain stage into a valve amp, or as a way to add tube warmth to a solid state or modeling rig1.
What the Thespian does
The Thespian is a preamp in a box: it shapes your fundamental tone with a Fender-style tone stack, and it does so with a real tube rather than a simulation. Master Effects positions it for three uses. Run it always-on to shape your core sound. Put it in front of a valve amp and use it as an added gain stage. Or run it into a solid state amp or a modeling setup, where the maker says it adds tube warmth that those rigs lack1. For bass players, that makes it a candidate for the front of the board, sitting alongside other preamp pedals as an always-on tone shaper.
Controls
The Thespian keeps things simple: a Volume, Treble, Middle, and Bass control, plus two switches1.
| Control | What it does |
|---|---|
| Volume | Sets overall output level1 |
| Treble | Treble cut/boost within the tone stack1 |
| Middle | Midrange cut/boost within the tone stack1 |
| Bass | Bass cut/boost within the tone stack1 |
| Bright switch | Engages a treble peaker capacitor to give a brighter sound at lower volume levels1 |
| Mid Boost switch | Shifts the inherent mid scoop of the Fender tone stack from 360Hz to 170Hz while giving about an 8 dB boost to the frequencies around 360Hz to 1kHz1 |
The Mid Boost switch is worth understanding if you know the Fender sound. The Fender tone stack naturally scoops the mids, and that scoop sits around 360Hz. The Mid Boost switch moves that scoop down to 170Hz and adds roughly 8 dB around 360Hz to 1kHz, filling in the low-mid and midrange that the stock circuit pulls away. For bass, that is often the difference between sitting back in a mix and pushing forward through it1.
Power and switching
The Thespian needs more current than a typical pedal. It uses a switching power supply (SMPS) to boost a 9-12VDC/500mA input up to the 200V the tube's plate needs, and Master Effects says a standard 2.1mm Boss-style power adapter is required, though one is not included1. The maker's support page confirms the pedal requires a 9V/500mA power source2.
The Thespian draws 500mA, which rules out most daisy-chain supplies and low-output isolated supplies. Plan for a dedicated high-current output on your power supply.
On the protection side, the pedal includes overvoltage and reverse polarity protection circuitry, ESD protection, and an internal re-settable fuse1. Switching is handled by a soft-touch footswitch that drives a relay, which Master Effects says gives the ultimate in reliability, and the signal path is solid copper with true bypass1.
The 2023 rework
Master Effects reworked the Thespian for 2023, with a smaller enclosure and an optimized power supply. The maker says the redesign came about due to parts supply issues with the original version. As part of the rework, the PCB was converted from the previous 2-layer design to a new 4-layer design with dedicated power and ground layers1.
The valve sits safely inside a 1590BB2 enclosure with side vents, powdercoated with UV printed artwork. The voltage regulators are attached to the enclosure to act as a heat sink1.
Price and availability
Master Effects lists the Thespian at $469US plus shipping, with shipping within Canada and the US at $20US. Orders typically ship within 2-4 weeks. Each pedal comes with a 1 year warranty on parts and labor, excluding damage from an improper power supply or misuse1.
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Questions
What tube does the Master Effects Thespian use?
The Thespian uses a 12AU7 preamp tube running at a 200V plate voltage. The pedal takes a 9-12VDC input and uses a switching power supply to boost that up to the 200V the tube needs, which is higher than many tube pedals run. The valve sits inside a 1590BB2 enclosure with side vents, and the voltage regulators are attached to the enclosure to act as a heat sink.
Does the Thespian come with a power supply?
No. Master Effects says a standard 2.1mm Boss-style power adapter is required but not included. The pedal needs a 9V/500mA power source, which rules out most daisy-chain supplies and battery power. The pedal includes overvoltage and reverse polarity protection, ESD protection, and an internal re-settable fuse.
Is the Thespian true bypass?
Yes. Switching is handled by a soft-touch footswitch that drives a relay, which Master Effects says gives the ultimate in reliability. The signal path is solid copper, and the pedal is true bypass when off.
Can the Thespian be used with guitar and bass?
Yes. Master Effects describes it as a classic preamp for guitar and bass. Because it is a recreation of the Fender Dual Showman and Alembic F-2B preamp circuits, it works as an always-on tone shaper, a gain stage into a valve amp, or a way to add tube warmth to solid state or modeling rigs.
Where is the Thespian made?
The Thespian is proudly assembled by hand in Calgary, Alberta, Canada by Master Effects. Each pedal carries a one year warranty on parts and labour, excluding damage from an improper power supply or misuse.
What does the Mid Boost switch do on the Thespian?
The Mid Boost switch shifts the inherent mid scoop of the Fender tone stack from 360Hz down to 170Hz while giving about an 8 dB boost to the frequencies around 360Hz to 1kHz. In plain terms, it fills in the scooped middle that the Fender-style circuit naturally has, which can help a bass or guitar cut through a mix.
Sources (2)
- Thespian Valve Preamp, Master Effects
- Master Effects Pedals, Master Effects