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.

In his later career Jack utilised a Samson wireless unit which freed him to roam the stage.  He employed no effects.  His amplification consisted of a Hartke 7000 head, driving four Hartke XL cabinets: two 4x10s and two 1x15s.   Jack set the graphic EQ on the head to a "frown" to boost the midrange.  He hit the strings hard, producing a punchy, thick, slightly distorted tone.

In 2012 Warwick issued the Jack Bruce JB3 Signature Survivor Bass.  The JB3's design is based on the Warwick Jack Bruce CRB Bass, an instrument released by Warwick on the occasion of Cream's 2005 Royal Albert Hall reunion concerts.  Jack commented on the JB3: "For many years after I found the fabulous Warwick Thumb Bass we struggled to come up with my idea of the perfect players' instrument. At long last here it is. The Jack Bruce JB3 Survivor Bass. The best there is."

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 bass that served thereafter as his main instrument.   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 preferred to use S.I.T. medium gauge roundwound strings (.050 - .105).   Jack occasionally used some Warwick 5-string basses for recording, though he didn't perform with them onstage.  In 2010 he acquired a fretless Star Bass II at Warwick's New York City custom shop.  For fretted bass playing Jack occasionally made use of a refitted Gibson EB-1 bass.