time, with Jack Bruce of Cream and Noel Redding of the Jimi Hendrix Experience both following suit. Entwistle also experimented throughout his career with "bi-amplification," where the higher frequencies of the bass sound are divided from the lower frequencies, with each frequency range sent to separate amplifiers and speakers. This allows for more control over the tone, because each portion of the frequency range can then be modified (e.g., in terms of tone, added overdrive, etc.) individually. The Versatone Pan-O-Flex amplifier used a different approach to bi-amplification, with separate amplifier sections for bass and treble but a single 12-inch speaker. The Versatone was used by well-known bassists such as Jack Casady and Carol Kaye. Grateful Dead bassist Phil Lesh used an unusual method of bass amplification which was part of the band's 1970s Wall of Sound (Grateful Dead) PA system. The signal from each string on the bass was sent to its own amplifier and speakers. This added a wider spatial effect to the bass and also reduced the Intermodulation distortion between the strings. In later years, Lesh's bass signal was so powerful that fans dubbed the area in front of his speakers the Phil Zone, which was referenced in the band's CD Fallout from the Phil Zone. 1980s–2010s In the 1980s the role of bass in popular and rock music evolved to become more melodic rather than simply providing a rhythmic function. The amplifier brand strongly identified with this new, 'scooped' sound (with strong bass and treble boost and mid-cut) was Trace Elliot. There were several features which made their amplifiers unique: the GP11 pre-amp featured 11 graphic EQ bands which were very broad bands, overlapping each other, thereby enabling massive amounts of frequency cut or boost when adjacent bands were boosted or cut. Secondly, the frequency bands were spaced closer together towards the bass end allowing even more variation for bass guitarists to alter their sound like no other amp had previously allowed. Added to this were MOSFET poweramps of 250 or 500 watts and the option of bi-amplified systems where bass and upper frequencies are filtered before being separately amplified and fed to dedicated high frequency and low frequency speaker cabinets. Trace Elliot gained a reputation for themselves; rumour has it that early users were John Paul Jones of Led Zeppelin, Andy Rourke of The Smiths and Brian Helicopter of punk band The Shapes. Mark King of