The Gray Matter is a dual overdrive and distortion preamp pedal from Loophole Pedals. It packs two circuits based on the DOD250 preamp into one enclosure, and the two sides can be set independently: the maker describes using one as a textured boost and the other as a light overdrive or medium-gain distortion. Guitar Pedal X noted it is "a little more granular in its output - with one extra variable control per side, and some interesting clipping options" compared with the pedal it draws on.1
Two DOD 250 drives in one pedal
The DOD250 is a classic overdrive/distortion preamp design, and the Gray Matter puts two of them side by side. Loophole Pedals describes starting from the vintage gray version of the '77 DOD250 preamp, which is where the pedal's name comes from, and then reworking the circuit21:
"I started designing GREY MATTER from a skeleton of the vintage grey version, '77 DOD250 preamp (hence the name.) I made many improvements for stability and tone and added edge control for hard clipping saturation."
Because each channel is a full drive circuit with its own footswitch, the pedal can cover more ground than a single overdrive: Delicious Audio suggests setting one side as a textured boost and the other as a light overdrive or medium gain distortion, or stacking the two for more gain.2 For context on how this design compares with other two-in-one drives, Guitar Pedal X includes it in a feature on compact stackable dual overdrives, calling it "a little more granular in its output - with one extra variable control per side, and some interesting clipping options."1
The controls and the Sense clipping switch
Each channel carries the same set of controls, so the two sides work identically apart from their clipping diodes.21
| Control | What it does |
|---|---|
| Gain | Sets the drive amount on each channel2 |
| Edge | Controls diode saturation, the hard clipping stage2 |
| Volume | Sets each channel's output level2 |
| Sense (toggle) | Three-way switch that sets the hard clipping diodes placed after the gain section2 |
| Footswitch | One per channel, left and right1 |
The Sense toggle is what separates the Gray Matter from a straight DOD250 pair. Its three positions work like this:2
- Up: BAT41 Schottky diodes on the blue side, 1N270 germanium diodes on the green side, both using symmetrical clipping for a balanced distortion.
- Middle: bypasses the hard clipping stage and the Edge control entirely, letting the LM741 op-amp be driven naturally.
- Down: the original silicon diodes of the gray '77 DOD250, again with symmetrical clipping.
The two channels use different diode sets in the up position: the blue side equips BAT41 Schottky diodes while the green side has 1N270 germanium diodes, so the same Sense setting gives each channel a different clipping character.2
Guitar Pedal X's controls listing matches this layout, with each channel's clipping options given as GE 1M270 / None / Silicon on the left channel and BAT41 Schottky / None / Silicon on the right.1
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Questions
Can you stack both channels on the Grey Matter?
Yes. The Grey Matter holds two individual drive circuits, and Delicious Audio's product page says you can run them individually or stacked. The two footswitches sit close enough together that you can switch between channels with one stomp, but far enough apart to stomp each one on its own, so one side can be set as a textured boost and the other as a light overdrive or medium gain distortion.
What diodes does the Loophole Grey Matter use?
Each channel has a three-way Sense toggle that sets the hard clipping diodes placed after the gain section. The up position uses BAT41 Schottky diodes on the blue side and 1N270 germanium diodes on the green side, both with symmetrical clipping. The down position uses the original silicon diodes of the gray '77 DOD250, also with symmetrical clipping. The middle position bypasses the hard clipping stage entirely.
Is the Grey Matter analog?
Yes. Delicious Audio describes the Grey Matter as 100 percent analog, built with respected components, and the circuit drives an LM741 op-amp, the same op-amp type found in the DOD250 preamp the pedal is based on.
Where are Loophole Pedals made?
The Grey Matter is handmade in Texas, according to Delicious Audio's product page for the pedal.
Sources (2)
- Guitar Pedal X, Guitar Pedal X, 2025-05-15
- New Pedals: Loophole Pedals Greymatter, Delicious Audio, 2019-06-24
