Subject of much confusion! Below is 'the picture worth 1000 words' showing how the Spider Jam inputs are processed.
The MIC channel has its own set of controls accessed by pressing SETTINGS/TONE twice, and presets accessed by pressing SETTINGS/TONE once.
The MIC level is set by pressing the INPUT LEVEL button twice and choosing MIC in the LCD screen with the 4-way cursor knob. Use the large Select knob to adjust the volume.
You will notice that the volume goes from OFF to -60dB ... 0dB ... +12dB in the LCD screen. This control is the equivalent of the Guitar Channel Volume. The LEVEL knob on the input panel is equivalent to Guitar Drive control but is intended to compensate for different microphone sensitivies not to add distortion. The MIC preamp can get noisy if it is pushed above -10dB.
The GUITAR channel uses the main controls on the top and front of the amp to set the amp models, EQ, effects and reverb and also has a substantial set of presets. The Channel Vol knob is used to adjust the relative level in any mix and, as it is saved with user presets, can be used to set all the different user presets to the same volume level.
AUX is not a channel at all. It is just an input jack that can be routed to either the MIC or GUITAR channel by holding down the GUITAR MIX/AUX button and then turning the large 'Select' knob to get the appropriate channel. This is represented by the red square in the diagram.
Despite what it says, AUX is not really 'mixed', with MIC or Guitar. It is just switched to either of the two channels MIC or GUITAR. It can be 'balanced' with the channel that it is not being routed to or with the CD/MP3 input by pressing the INPUT LEVEL button twice and choosing AUX.
This is a simple straight through input with no processing whatsoever but its relative level can be adjusted by pressing the INPUT LEVEL button twice and choosing CD. Although the Spider Jam itself plays the CD/MP3 input in mono, it passes it throught to the two RCA jacks on the back as stereo.
Apart from the MP3/CD players mentioned, you can also plug an effects pedal such as a POD in here if you have the correct cable.
