The Great Eastern FX Co. Distortion Filter D312A is an analog distortion pedal designed and built in England, and it is a limited item: 165 units, capped by the scarcity of its core components12. What sets it apart from an ordinary distortion box is a second half of the circuit. It combines distortion with an active filter section inspired by classic studio filter and synthesizer concepts, so after the drive stage you can carve the distorted signal with a band-pass filter rather than just shaping it with a tone control1.
RockBoard's PedalPedia describes the result as thick, aggressive distortion that can be sculpted using a resonant low-pass filter control, ranging from tight, focused drive to heavily saturated textures1. Delicious Audio called it "a limited pedal that reimagines classic hard-clipping circuits through the lens of rare, obsolete components"2.
The controls: Gain, Level, Frequency and Depth
Four knobs run the pedal. Gain and Level set the core output, and the two filter knobs do the sculpting on top3.
| Control | What it does |
|---|---|
| Gain | Sets the drive level, together with Level it forms the core output3 |
| Level | Sets the output volume alongside Gain3 |
| Frequency | Sweeps the mids-leaning filter from 300Hz to 900Hz34 |
| Depth | Fine-tunes the filter boost, plus or minus; its impact increases the higher the Frequency is set34 |
The Frequency control is largely mids-leaning, and the Depth knob works in both directions from wherever the Frequency knob sits. Because Depth's effect grows as Frequency rises, the top of the sweep is where small Depth adjustments change the character most3. Delicious Audio describes the range this gives players: "anything from a subtle mid-emphasis to extreme, 'cocked-wah' textures reminiscent of stoner rock"2. Guitar Pedal X's reviewer Stefan Karlsson found the same thing from the playing side: "Beyond he mid-way point of the Filter Sweep - you're largely in sort of cocked wah territory"3.
How the clipping works: three Soviet D312A diodes
The distortion itself comes from hard clipping, but not the usual silicon pair. At the core of the pedal are three NOS Soviet-era D312A germanium diodes, configured for asymmetrical clipping: two diodes on one side of the wave and one on the other23. Karlsson describes that arrangement as slightly louder, more aggressive and more amp-like than symmetrical clipping, and aimed at maximum harmonics and texture3.
Germanium clipping has a trade-off the reviewer flags plainly: it results in some degree of volume drop, which the asymmetrical arrangement offsets3. Delicious Audio frames the whole design as "a significant departure from the symmetrical silicon pairs found in its predecessors," producing a distortion rich in harmonic complexity and dynamic response2.
How it compares with the DOD 250 and MXR Distortion+
The circuit sits in a familiar lineage. Karlsson calls it "Kind of a little based on the DOD250 - but so much more," and places it adjacent to both the DOD 250 and the MXR Distortion+, with similar gain and volume levels but richer texture thanks to the filter and the asymmetrical germanium clipping34. Where those two classics give you gain and output and little else, the D312A adds the vocal mid-range character of its band-pass filter, sculpted by the dedicated Frequency and Depth knobs2.
One practical note from the review: at unity levels at its peak, the pedal can occasionally use a little help on the output side. Karlsson often added a Strymon Sunset treble booster after it3.
"Texturally is sounds glorious on its own - but occasionally needs a little augmentation on the output side."
A limited run in the Obsolete Devices series
The D312A is the second pedal in Great Eastern FX Co.'s Obsolete Devices series, a line built around components that are no longer manufactured3. The run was limited to 165 units because the Soviet D312A germanium diodes at its heart are long discontinued and available only as new-old-stock parts23. As of the November 2025 review it was available from the Great Eastern FX Co. webstore, and the reviewer picked up his copy at Witney Pedal Party 43.
The D312A is a limited edition of 165 units. Once the stock of NOS Soviet diodes is used up, more cannot be built, so availability depends on what remains23.
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Questions
How many Great Eastern FX D312A Distortion Filter pedals were made?
The run was limited to 165 units. Great Eastern FX Co. capped production because the core components, NOS Soviet-era D312A germanium diodes, are scarce, so once the diode stock is gone no more can be built.
What does the Depth knob do on the D312A?
Depth fine-tunes the filter boost, and it works in both directions, adding or cutting. Its impact increases the higher you set the Frequency knob, so at the top of the 300Hz to 900Hz sweep a small Depth change makes a big difference, from subtle mid emphasis to extreme cocked-wah textures.
What power supply does the D312A Distortion Filter need?
It runs on 9V DC with a center-negative plug, the standard used by most modern pedal power supplies. The circuit is analog, and the pedal sits in a robust metal enclosure built for pedalboard use.
Where is the Great Eastern FX D312A built?
It is designed and built in England. It is the second release in the maker's Obsolete Devices series, a line built around rare and discontinued electronic components.
How does the D312A compare with the DOD 250 and MXR Distortion+?
Guitar Pedal X's reviewer places it adjacent to those two classics, with similar gain and volume levels but richer texture, and calls it kind of a little based on the DOD 250, but so much more. The difference comes from the asymmetrical germanium clipping and the onboard filter, which neither classic has.
Is the D312A Distortion Filter still available?
As of the November 2025 review it was available from the Great Eastern FX Co. webstore, and the reviewer bought his copy at Witney Pedal Party 4. Because the run is capped at 165 units built from scarce Soviet diodes, availability depends on remaining stock.
Sources (4)
- Distortion Filter D312A by Great Eastern FX Co., RockBoard PedalPedia, 2026
- New (LTD) Pedal: Great Eastern FX Distortion Filter D312A, Delicious Audio, 2025-11-19
- Guitar Pedal X, Guitar Pedal X, 2025-11-19
- Guitar Pedal X, Guitar Pedal X, 2025-12-05
