Set the “Gain” control to around “5,” or in the center of the dial. This controls how much your guitar's signal is boosted before going to the amplifier’s effects. High gain results in distortion, not commonly sought after in jazz music. Choose a “Gain” level of between “4” and “6” to get a bit of distortion to add some edge to your tone, or choose a lower one if you wish to have an especially clean tone.
Choose your volume level. Bear in mind that the “Gain” setting also increases the volume of your amp, so the “Volume” control can be balanced with it for the best effect. If you have a high gain, you can have a lower volume. Choose a volume just over halfway, but lower this if you need to be quiet.
Set the “Treble” dial to either be just above or just below “5.” Jazz players rarely use treble-heavy amp sounds. You can experiment as you choose, but if you want a characteristic jazz tone, keep the treble below “7.”
Decide whether to have a chunky, bass-heavy tone or a balanced one. A balanced tone sounds cleaner, but some players prefer a “fat” jazz tone to a balanced one. Adjust the “Bass” and “Mid” controls according to your preference. Choose one for now, and remember you can always change it later. For a bass-heavy tone, turn the “Mid” and “Bass” dials to around “8” or “9,” and for a balanced tone, turn them to “3” or “4.” Bass-heavy tones should be accompanied by low treble; balanced tones can have a higher treble.
Select your reverb level. This controls the amount of reverberation in the sound. Most jazz players use a reverb of between “2” and “4,” but this can be altered. Turn the “Reverb” control up high and test it to gain a better understanding of its effect. Set your “Master” dial to around halfway and try out your jazz tone. Make adjustments as desired.