Great Eastern FX D312A Distortion Filter

The Great Eastern FX Co. D312A Distortion Filter is a limited-edition analog distortion pedal with an active filter section, designed and built in England¹. It is the second release in the company's Obsolete Devices series, a line built around rare, obsolete components, and it uses three long-discontinued Soviet D312A germanium diodes in an asymmetrical clipping arrangement². The run was limited to 165 units because of the scarcity of those diodes³.

What makes it different from a standard distortion pedal is the filter. Delicious Audio described it as "a playable artifact of electronic history based on a classic gain structure," with a band-pass filter that sculpts a vocal mid-range character³. Guitar Pedal X's reviewer called it "the beautifully textured and expansive Distortion Filter"².

Distortion with a resonant mid-range filter

The pedal combines a hard-clipping distortion stage with a resonant filter that RockBoard's PedalPedia says produces "thick, aggressive distortion that can be sculpted using a resonant low-pass filter control," delivering everything from tight, focused drive to heavily saturated textures¹. Delicious Audio reported that the circuit produces "a distortion rich in harmonic complexity and dynamic response, a significant departure from the symmetrical silicon pairs found in its predecessors"³.

The filter itself is mid-range focused. Guitar Pedal X's reviewer found that "the Filter is largely Mids-leaning and takes you from 300Hz to 900Hz," and that beyond the mid-way point of the sweep "you're largely in sort of cocked wah territory"². Delicious Audio similarly noted that the Frequency and Depth knobs let players dial in anything from a subtle mid-emphasis to extreme, cocked-wah textures reminiscent of stoner rock³.

The controls: Gain, Level, Frequency and Depth

Four knobs run the pedal⁴. Gain and Level set the core output, while Frequency and Depth handle the filter².

The interaction between Frequency and Depth is worth knowing: the Depth control's effect grows as the Frequency knob moves up the scale, so the same Depth setting bites harder at 900Hz than it does at 300Hz²⁴.

Three Soviet germanium diodes in asymmetrical clipping

The heart of the pedal is its clipping stage: three NOS Soviet-era germanium diodes, configured for asymmetrical clipping, with two diodes on one side of the waveform and one on the other²³. Guitar Pedal X's reviewer explained the practical effect: "the slightly louder and more aggressive and amp-like Asymmetrical Clipping (2 Diodes on one side, and 1 Diode on the other)"².

That arrangement also serves a purpose beyond tone. Germanium clipping results in some degree of volume drop, and the asymmetrical layout offsets that by being slightly louder and more aggressive than a symmetrical pair would be².

Founder David Greeves has said the design was driven by the diodes themselves, aiming to make these vintage pulse-detector components "sing"³.

Where the circuit comes from

Guitar Pedal X's reviewer placed the pedal's lineage clearly: "this pedal is somewhat adjacent to the DOD250 and MXR Distortion+, while the Filter and that Asymmetrical Germanium Clipping" are what differentiate it, with similar gain and volume levels but richer texture². In his year-end round-up he put it more simply: "Kind of a little based on the DOD250, but so much more"⁴.

Output level and boosting an amp

One practical point from the review: the pedal can run short on output. Guitar Pedal X's reviewer found that "texturally it sounds glorious on its own, but occasionally needs a little augmentation on the output side" at unity levels, and he often added a Strymon Sunset treble booster after it². Players who want to use it to push an amp into distortion may want a boost pedal after it.

Videos

Click to load

Click to load

Questions