Just a quick and simple mod to get more use out of this pedal. Take it apart, drill a hole, remove the tiny toggle switch (desolder), wire in a new SPDT switch. I placed it on the upper right side so it would fit.
One side is the stock ZW44, flipping the switch adds a 10K resistor into a certain spot of the circuit, giving the GT-OD sound. The GT-OD has more mids and bass, and slight volume bump. I am not an engineer but the resistor seems to be adding some bias voltage to the op amp in the tone control part of the circuit. I wish I knew a little more about how this works. It does work though.
In the past, I played a Washburn les paul through a MXR Classic Overdrive (a cheaper version of the GT-OD, pretty similar) through a Marshall Valvestate 2x12 amp for a band project I was in called Special Guest, and the sound I got was so exciting to me that I finally got to recreate it years later. Most of the gear was borrowed, and I lost the Classic Overdrive along the way.
I am using an Agile les paul with BurstBucker pickups through the GT-OD into a Marshall DSL100H amp head. I have to say, these are some killer tones. I have been chasing a sound that was in my head, and this was pretty much it. The amp and guitar has a lot to do with it, but the pedals are just sauce on the top.
I sort of prefer the ZW44 side of the toggle with this rig, because the bass can get so huge on the GT-OD side, due to the heavy bass and resonance settings on the Marshall amp.
Compared to the TS-9 Tube Screamer, the GT-OD gets a little better higher gain sound on its own, but the TS-9 is better for boosting the dirty channel of the DSL100H. Running the TS into the GT-OD is a lot of fun also. The GT-OD is a darker sounding pedal. It also is louder than the TS9.
It's no surprise that the GT-OD/ZW44 gets a good crunch tone since it is so closely based on the Boss SD-1. MXR has really dialed in this circuit though and it sounds vastly better than the SD-1. I have always had issues with those in the end.
Compared to the MXR Classic Overdrive, the GT-OD is build a lot better, the case is a lot heavier and thicker, and it just feels more solid and expensive. Totally worth the extra small amount of cash. The Classic Overdrive and Classic Distortion pedals are kind of chintzy feeling, kind of makes you squirm a bit. Guitar shops used to sell them for next to nothing. Feels good to upgrade to the real deal, and the real Marshall as well. I suppose all I am missing at this point is a guitar that says Gibson on the headstock.
I also need to mention how beautiful the metallic green finish looks in person, very nice. Does not come across in photos.