Onboard Passive Distortion Mod
Traditionally, to distort an audio signal, a powered device is used to boost, or "overdrive" the original signal. The GuitarHeads Underdrive does the opposite. It is a Passive Unit (no external power or batteries needed), that when in used in place of your standard Capacitor on your Tone Control Pot, the audio signal is "Clipped" to produce a gritty distorted tone. This is the method that was used to create some of the first "Fuzz" distortions, and is still being used today as a popular modification to many designs (including the Ibanez Tube Screamer).
This Mod was designed for guitars that are equipped with higher output pickups (the more output your pickups try to squeeze through the unit, the more effect it will have). It will still work with all different pickups, just not to the same degree. So we recommend using pickups with at least 10k Ohms of DC Resistance. It is also recommended that you use this Mod with Audio Tapered Control Pots, as they have a more gradual roll-off, and will allow you to more finely dial in the desired amount of effect mixed with your standard signal.
Your Amp Rig will also factor into the effect range. On an average Amp's Clean Channel, you can dial back your tone control to give you a Gritty Vintage Blues Drive, however since the amp is not creating any additional gain on this channel, you may notice a slight volume difference. On your Amp's Drive Channel, the effect of the Mod has less effect on your volume levels, but adds a nice layered distortion that will thicken up your sound, increase clarity & sustain, and add more "chug" to rhythm playing.