Colman Musical Instruments designs and builds interesting and innovative effects for musical instruments and audio. It is a one-man show from Elora, Ontario, Canada.

This mod is a collection of three separate modifications which have been selected to work together, creating a more advanced user interface for the Boss SD-1 Super OverDrive. This gives the user control over filter options, feedback options, and clipping options that are not available in the stock Boss SD-1, and extends the pedal’s tonal pallet to great expanses.

Negative Feedback Mod

The Negative Feedback Knob opens the voice of your SD-1 to yield a fuller and more resonant sound, which you will certainly get carried away with. Its a pretty cool technique, and it's used in a lot old great amps. Look it up on Wikipedia if you're interested.

Critically Over-Fed-Back Mode

The critically over-fed-back mode occurs when the effect is provided with "too much" negative feedback. The SD-1 should not hurt itself in this configuration, since the inputs of the op amp Boss uses are quite robust, and the overall circuit is not capable of generating a voltage large enough to damage the circuit on its own, when powered at OV. The battery snap has been removed, so you need to use a wired power supply. Please only power the circuit at 9V like Boss say to.

The negative feedback effect increases until it reaches a maximum of nastiness and snarl, and then it sometimes cleans up a bit depending on the stock effect's part tolerances and the added parts' tolerances. When this mode is reached, the three knobs on the front will either become inert and the pedal becomes a lovely clean preamp, or the knobs will begin to control different gain textures.

Resonant Tone Mod

The Resonant Tone Mod alters the tone circuit to make it somewhat more like a Wah pedal's filter, but also not really. This mod gooses the cutoff of the stock tone filter a bit, giving a little boost at that frequency, a general resonance to the effect.

Diode Selection Mod

The diode selection mod offers control over each diode in the clipping section of the SD-1. While the other two mods can be switched oft, since l have entirely removed the original diodes, this mod is constantly active. Different combinations of diodes will yield different characters to the distortion that this effect produces.

CONTROLS

Feedback Knob

This section refers to the additional knob now found on the left side of your SD-1. This knob provides the effect circuit with global negative feedback. This means that the output of the amplifier is fed back into the input of the amplifier (but operational amplifiers have 2 inputs, and we choose the "not-more" input, while the guitar signal goes to the "more" input), which provides the effect with greater headroom, and causes more significant distortion once the threshold for breakup is crossed. Each unit will react differently due to component differences, but each obeys the same principle.

The knob has a switch, which is off when the top of the knob is rolled away from you (it will click). When the switch has clicked, the Negative Feedback Mod is inactive. Roll the switch toward you to add negative feedback.

Filter Selector

This section refers to the additional switch on the left side of the SD-1, beside the Feedback Knob. This controls the Resonant Tone Mod, and the switch has three positions. The switch applies different filers to the effect signal depending on the position of the Tone Knob. When the switch points straight out, the mod is inactive.

Diode Switches

Since the SD-1 uses soft clipping to generate much of its overdrive, it uses three diodes in the feedback of one of its op amps. These diodes are arranged in a series pair in parallel with another single diode. Google the SD-1 schematic to see a picture.

The single diode is controlled by the three-position toggle switch on the front of the pedal, in the middle. When the switch points straight out, a germanium diode is used. When the switch points up or down, another diode is added in parallel to that one.

The series pair of diodes is controlled by the two switches on either side of the front panel of the pedal, one per diode. Each switch has two positions, allowing for four different combinations of diode in that branch of the circuit.

Some changes may be subtle, and some may be more of a feel thing, but they are all interesting in some context, and are sure to craw something great out of your playing.

WARNING

Product may cause involuntary facial movements, spontaneous vocalization, and body contortion. You like that daddy? 

Please SMILE, LAUGH, and DANCE responsibly as you PLAY