If you've used the TPA-200B you are most certainly familiar with the incredible array of tones you can get just by changing the balance between the input and output controls. Higher output with lower input yields a clean, clear, open sound, while higher input level and lower output level reveals more overtones and harder drive, all the way up to a sweet, thick distortion. Want more? Try this to get a riot of distortion.
Take an XLR female to TRS cable and run it from the output of channel one into the line input of channel two. Switch channel two to accept Line Input. Run the output of channel two to your recording device or live rig. Plug into channel one (mic, Hi-Z, or line level). Now you have THREE levels to adjust the distortion level with the output level on channel two as your master level. Talk about tone control!
This works great in a few different applications. First, it's great for during a mix. Use the line level input on channel 1 and insert the TPA-200B on the channel you want distorted. I love it on keyboards personally, it hugely increases the timbres I can get and erases any digital edge to the sound. It can also sound good on guitar, bass, even vocals for a special effect (try blending it with an undistorted track). This effect also works great when tracking guitar or bass through the Hi-Z input. Lastly, using the TPA-200B as a mic pre and purposely distorting the signal while recording can really make a track stand out when it comes time to mix!