The Mad Professor Sky Blue is an overdrive pedal built in the Dumble style, aimed at the voicing of the Dumble Overdrive Special HRM Hot Rubber Monkey Edition. Guitar Pedal X's Stefan Karlsson described it as "a very unique take on the Dumble Overdrive Special HRM Hot Rubber Monkey Edition"1. It is one of two Dumble-inspired pedals the maker has produced, and it is a distinct design from the other one, the Simble1.
What it does
The Sky Blue is a Dumble-style overdrive: rather than copying a Tube Screamer or Bluesbreaker circuit, it goes after the touch-sensitive, harmonically rich breakup associated with the Overdrive Special amp's Hot Rubber Monkey voicing. Its four controls shape that voicing directly1.
| Control | What it does |
|---|---|
| Volume | Output level1 |
| Distortion | Amount of drive1 |
| Z | Input load / impedance1 |
| Texture | From more compressed to treble boost1 |
The Z control, which sets how the pedal loads the guitar's pickups, and the Texture control, which moves between compression and treble boost, are what set the Sky Blue apart from more conventional overdrive pedals1.
Dialling it in
Karlsson found the pedal takes some patience to set up, and shared the settings that worked for him: "I get the best results with Volume @ 3 o'c Distortion @ 10 o'c, Z @ 8 o'c, and Texture @ 4 o'c"1. His overall verdict was that the Sky Blue is "a little fiddly on the dial-in, but still a very intriguing proposition", with a fairly distinct signature breakup, and that the dial-in rewards patience1.
Availability and price
The Sky Blue is discontinued1. When new it carried a list price of €269 / $289 / £269, in line with Mad Professor's recent Hand Wired series pedals, which are priced at €330 / $380 / £3301. Because the pedal is out of production, used examples change hands at a premium: Guitar Pedal X noted "some very pricey Sky Blues in Japan, each going for around £350+", with the dearest currently priced at £5891.
The Sky Blue is no longer in production. Used prices, particularly in Japan, run well above the original list price1.
Videos
ProGuitarShopDemos
Mad Professor Amplification
Mad Professor Amplification
Sources (1)
- Guitar Pedal X, Guitar Pedal X, 2026-01-23
