Ibanez Fat Cat distortion pedal (Ibanez FC-10 Fat Cat Distortion) is good for blues, rock, pop, alternative, but not for metal. You can hear the fat tone even at maximum overdrive. Here is the circuit schematic diagram.
You can see the the first transistor 2SC1815/BC546 is configured as voltage follower, giving a high impedance for the input. The op-amp (5534 IC) serve an adjustable gain amplifier, to boost the signal until it reach the forward bias voltage (about 0.6 volt) of two 1N4148 diodes, where the signal is clipped.
The tone controller is very simple, just adding a high frequency attenuation when the resistance is set to higher value. Finally, 2SK188/BF245 field effect transistor (FET) is used to buffer the tone control circuit to give low impedance output. Without this buffer, the tone controller would also act like a volume control when the output is connected to a low impedance input.