The Master Effects Seventh Son is an analog preamp pedal that puts the preamp of the vintage Gallien-Krueger 250ML lunchbox amplifier from the late 1980s into a pedal format1. RockBoard's PedalPedia lists it as an equalizer preamp2. It comes in two versions: a "Classic" version that is faithful to the original amplifier, and a "Modern" version that offers improved clarity and removes the muddiness from the tone stack1.
Controls
The Seventh Son keeps the layout simple: a four-band active EQ, a master volume, and a gain toggle switch1.
| Control | What it does |
|---|---|
| EQ (4-band active) | Boost and cut at 8.0 kHz, 2.0 kHz, 500 Hz and 120 Hz1 |
| Volume | Master volume control1 |
| Gain (toggle switch) | Switches between a lower gain crunch and a more saturated higher gain setting1 |
The four-band active EQ with boost and cut is the heart of the pedal, and it is what carried over from the 250ML amplifier design1. Players who want more tone-shaping options in a preamp can compare it with other circuits in the maker's range, such as the Master Effects Tetragon or the Master Effects JC-Pre.
Classic and Modern versions
Master Effects offers the Seventh Son in two versions1:
- Classic: faithful to the original Gallien-Krueger 250ML amplifier, priced at $229US plus shipping1
- Modern: offers improved clarity and removes the muddiness from the tone stack, priced at $249US plus shipping1
Shipping within Canada and the US is $20US, and shipping to the UK, Western Europe, Australia and Japan is approximately $60US1.
Power and build
The pedal runs from a standard Boss-style 9V power supply1. Inside, there is circuitry that generates a ±15V power supply, just as the original 250ML amplifiers used1. Each pedal uses a professionally assembled PCB and is assembled by hand in Calgary, Alberta, Canada1.
Master Effects gives each pedal a 1 year warranty on parts and labor. The warranty does not cover damage due to using an improper power supply or other misuse1.
Questions
What amp is the Master Effects Seventh Son based on?
The Seventh Son is based on the preamp found in the vintage Gallien-Krueger 250ML lunchbox amplifier from the late 1980s. Master Effects offers two versions: the Classic, which is faithful to the original amplifier, and the Modern, which offers improved clarity and removes the muddiness from the tone stack.
What is the difference between the Classic and Modern versions?
The Classic version is faithful to the original Gallien-Krueger 250ML amplifier, while the Modern version offers improved clarity and removes the muddiness from the tone stack. The Classic lists at $229US plus shipping and the Modern at $249US plus shipping, as of the maker's product page dated 26 October 2026.
Is the Seventh Son true bypass?
Yes. Master Effects lists the Seventh Son as true bypass, and the circuit is analog throughout.
Is the Seventh Son analog?
Yes. The Seventh Son is an analog preamp pedal, and it is listed as an equalizer preamp on RockBoard's PedalPedia.
Where is the Master Effects Seventh Son built?
Each Seventh Son uses a professionally assembled PCB and is assembled by hand in Calgary, Alberta, Canada, according to Master Effects.
Sources (2)
- Seventh Son, Master Effects
- Seventh Son by Master Effects, RockBoard PedalPedia, 2026
