Electro-Harmonix Holy Grail Reverb
First widely-affordable Spin-FV1-style digital reverb — Spring, Hall, and Flerb in a small box.
We don't ship reference schematics until they've been hand-authored against authoritative sources (manufacturer service docs, ElectroSmash analyses, GEOFEX writeups) and reviewed in the simulator. Until then, the BOM, signal chain, controls and mod notes below are accurate, and you can still add this pedal to a project — it just won't include a circuit yet.
About
Built around the Spin Semiconductor FV-1 DSP, which holds three internal reverb algorithms (Spring, Hall, and Flerb — a flanged reverb). Mono in/out, single Reverb knob, single algorithm switch. The simplicity is the appeal: it just sounds good without menus.
Signal chain preview
5 stagesQuick facts
- Almost single-handedly popularized the Spin FV-1 chip on the pedal market.
- The Flerb setting is a Holy Grail signature — a flanger swirling inside the reverb tail.
- Newer Holy Grail Plus, Max, and Neo all build on the same FV-1 platform with more algorithms.
Controls
- Reverb (wet level)
- Mode switch (Spring / Hall / Flerb)
Mod recipes Pro
3 mods- Custom EEPROM programs
Load your own reverb / delay / pitch programs.
How: Reflash the 24LC32 with SpinASM-compiled programs (Plate, Shimmer, Reverse). Maintain the same I²C pinout as the stock chip.
- Stereo output
Tap both FV-1 DACs for true stereo wet.
How: Add a second output jack tied to the FV-1's DACR output through its own buffer / mix stage. Mono in, stereo wet out.
- Wet/dry kill switch
Cuts the dry path for ambient wet-only swells.
How: Add an SPDT toggle muting the dry mix resistor — only the wet signal reaches the output.