The treble and normal channels are combined (mixed) together with the mixer circuit. The mixer is comprised of two resistors and a capacitor. The mixer resistors form a voltage divider that combines the two channels. The mixer resistors also reduce the output level of the preceding gain stages (V1A and V1B). The classic value for these resistors is 470K, but the JTM45 uses 270K resistors. Some people lower the value of these resistors to get more gain, but this affects the frequency response of the treble channel too. The mixer bypass cap forms a 10dB/decade rising treble slope for the treble channel only.
