One of the most revered vintage compressors was created by Ross, using modified Dyna Comp circuitry. The Keeley 4-Knob Compressor, regarded as one of the best boutique examples, is derived from that. "It sounds great: a quality compression with adjustments to suit pro players" Available in two versions, this four-knob unit adds attack and clipping knobs over the original (£165), which instead incorporates them as internal trim pots. Level and sustain are similar to a Dyna Comp's, and that clipping knob adjusts the input level (with different settings to suit humbuckers and signal coils) so they don't add distortion to the signal.