The Mad Professor Hand-Wired Sky Blue Overdrive (SBOD) is a four-knob overdrive pedal from Mad Professor. It is a take on the Dumble Overdrive Special HRM Hot Rubber Monkey Edition, and Guitar Pedal X describes it as "a very unique take on" that circuit1.
The original Sky Blue is discontinued, and as of August 2025 it had not been re-issued in Mad Professor's relaunched Hand Wired series2.
The controls: Volume, Distort, Texture and Z
The SBOD's four knobs are Volume, Distortion, Z and Texture1. Two of them, Z and Texture, are unusual combination controls that set this pedal apart from most overdrives.
| Control | What it does |
|---|---|
| Volume | Sets the output level1 |
| Distort | Sets the amount of overdrive1 |
| Z | Increases input load, impedance and low-end1 |
| Texture | A mix of compression and EQ1 |
Texture is the character control. Guitar Pedal X describes it as "a mix of Compression and EQ", so turning it shifts both how saturated the breakup feels and how the pedal's overall tonal balance sits1.
Z is the input control. Guitar Pedal X notes that Z "increases input load / impedance / low-end"1. In practice, that means the same guitar can be made to interact with the pedal differently before the gain stage ever sees the signal.
For a starting point, Guitar Pedal X's Stefan Karlsson reports getting his best results with Volume at 3 o'clock, Distortion at 10 o'clock, Z at 8 o'clock, and Texture at 4 o'clock1.
How it differs from the Simble
Mad Professor has made more than one Dumble-style pedal, and the Sky Blue is quite distinct from the other one, the Simble1. The difference sits largely in the controls: the Sky Blue's Z and Texture knobs are combination controls that blend loading, compression and EQ in ways a conventional two- or three-knob overdrive does not1.
What reviewers said
Guitar Pedal X's Stefan Karlsson reviewed the Sky Blue in January 2026:
"The Sky Blue is quite a different 'Dumble' - a little fiddly on the dial-in, but still a very intriguing proposition with a fairly distinct signature breakup."
The same review notes that dial-in rewards patience overall, and that the pedal's signature breakup is fairly distinct1. On price, Karlsson points out that the recent Hand Wired Mad Professor pedals sit at €330 / $380 / £330, which made his own Sky Blue acquisition, at €269 / $289 / £269 when new, good value by comparison1. On the secondhand market, he found some very pricey Sky Blues in Japan, each going for around £350 or more, with the dearest one priced at £5891.
Where it came from and where to find one
The Sky Blue Overdrive was part of Mad Professor's earlier lineup, priced at €269 / $289 / £269 when new, and is now discontinued1. A Hand Wired Sky Blue Overdrive has since appeared in Mad Professor's Hand Wired range, but it is currently listed as sold out2.
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Questions
What does the Z knob do on the Sky Blue Overdrive?
Z increases the input load, impedance and low-end of the pedal's input stage, according to Guitar Pedal X's review. Turning it changes how your pickups interact with the pedal before the gain stage, so the same guitar can feel and respond differently depending on where Z is set. It is one of two unusual controls on the pedal, alongside Texture.
Is the Mad Professor Sky Blue Overdrive still made?
The original Sky Blue is discontinued, and as of August 2025 it had not been re-issued in Mad Professor's relaunched Hand Wired series. On the secondhand market, Guitar Pedal X found examples in Japan listed at around £350 or more, with the dearest one priced at £589.
Can the Sky Blue Overdrive push an already distorted amp?
The pedal is a Dumble-style overdrive, and its four controls, especially Distort and Texture, are laid out to shape breakup character and EQ together. Texture blends compression and EQ, so the same gain setting can be made more saturated or more open depending on where it is set.
Sources (2)
- Guitar Pedal X, Guitar Pedal X, 2026-01-23
- Guitar Pedal X, Guitar Pedal X, 2025-08-26
