This is an exact Tonebender MK1.5 pedal topology, but with a few part values tweaked a bit for better performance. We made the BIAS resistor adjustable on the BIAS knob in the center of the pedal, as there are some great sounds to be had by running higher bias than normal. It gets brighter and cuts through better when it's overbiased. Some people like the bias lower for a deeper but softer sound. There is also a blue BIAS trimpot inside to set the center setting of the BIAS knob. We set it at 5V at the shop and normally you should not need to use that. But at high or low temperatures it can come in handy if the bias changes.
We also changed a capacitor value slightly to make it sound and work better. In addition, we added the CLEAN trimpot like our Sun Face, as it helps preset the pedal for cleaner, or less bassy tones that some people like, especially with hotter pickups. These clean up with a nice crunchy sound when you turn the guitar or the clean trimpot down. We recently changed a resistor value slightly to make them a bit louder. Some people, especially with humbuckers, were complaining that the normal MK1.5 was not loud enough for them, so this should help. Simply copying a schematic would have been easier, but we want to make the pedal as great sounding as possible, and allow it to work with various guitars and amps.
So this is our updated take on a MK1.5 Tonebender.
The FUZZ knob is more useful on the Sun Bender than on a Fuzz Face/Sun Face, you can turn it down as much as you like and still get great tones.
These have an interesting, gradual cleanup, unlike a Fuzz Face which tends to get too clean too fast. Back a Tele down anywhere from 4-7 on it's volume knob, and with your picking attack you can go from almost clean to awesome Tweed amp distortion sounds up to a fuzzy tube amp distortion. Very natural sounding! The white CLEAN trimpot can be used to preset this less saturated, crunchy distortion sound.
I get asked about the differences between this and our MKIV Sun Bender a
lot. The MK1.5 is more raw and 1960s sounding, with a BIAS knob. MKIV is more saturated
and early 1970s sounding, and has a tone control that can go from thick to thin and trebly.
We have always used New Old Stock British Mullard transistors in this pedal:
In 2019 we got some outstanding Mullard CV-type military tested transistors, which are very consistent and sound great! These are dated 6927, made the 27th week or 1969, what a great era!!!
The on/off FUZZ pot is optional to allow disconnecting the battery without having to unplug the pedal, great when mounted in the middle of a pedalboard. Turn it down all the way and it CLICKS and turns off the power.
SIZE : MXR style box, 2 5/16" x 4 5/16" 1290 / 1590B
We decided to make this 2-transistor MK1.5 instead of the 3-transistor MK-II as we don't have many of these awesome British NOS Mullard transistors. Also we tested them side by side and found that an average MK-II really didn't sound better, just different. The MK1.5 is a bit easier to make consistent but they can still be tough as the circuit with NOS Mullards is very finicky. The MK-II is about the same circuit as an old Marshall Supa-Fuzz, you can hear the comparison below.
Here is what an original MK1.5 looks like, this rare pedal was on ebay at the end of 2012 for $5,000 but got no bids.