During the 1960s, Jack plugged his EB-3 into a stack of Marshall amps (Marshall 4x12s with Marshall 100 heads).  His desire for greater volume induced him to crank up the volume control, unwittingly producing the heavy, distorted tone that became so popular in the ensuing years.  Later, Jack had instrument technician Dan Armstrong install a diode into the EB-3's wiring to produce the same effect without overdriving his amplifiers.

Today, Jack utilises a Samson wireless unit which frees him to roam the stage.  He employs no effects.  His amplification consists of a Hartke 7000 head, driving four Hartke XL cabinets: two 4x10s and two 1x15s.   Jack sets the graphic EQ on the head to a "frown" which boosts the midrange.  He hits the strings hard, producing a punchy, thick, slightly distorted tone.

Though trained on the upright bass, Jack Bruce took a liking early on to small, short-scale electric basses.  One of his first was the Fender Bass VI, a 6-string bass tuned EADGBE like a guitar, but one octave lower.  Jack recorded most of Fresh Cream with this bass, before moving to the classic Gibson EB-3, the sound of which he made famous during Cream's live tours.

In 1976, Jack moved to the fretless bass.   After stints with some Aria and Spector long-scale basses, he found Warwick, a German producer of high quality electric basses.  Jack made some suggestions for improving the balance and pickups, and Warwick produced the instrument he now uses.   The Warwick Jack Bruce Signature Model is a modified fretless 4-string Thumb Bass featuring MEC active pickups and LED position markers on the side of the neck.  Jack strings his instrument with S.I.T. medium gauge roundwound strings (.050 - .105).   Jack also uses some Warwick 5-string basses for recording, though he doesn't use them onstage.  For fretted bass playing Jack occasionally makes use of a refitted Gibson EB-1 bass.