Tripple rectifier Fender Prosonic $850 3 position fixed bias

The Prosonic introduced several features that had previously been seldom, or never before, seen in Fender amplifiers. Its most unusual feature is the switchable rectifier and power amplifier bias scheme, allowing on-the-fly changes of operating mode and output power (as well as subjective tonal differences). This feature, originally found on Randall Smith’s Mesa Boogie amplifiers, allows the Prosonic to achieve a versatility very rarely seen from mass-market instrument manufacturers. The Prosonic’s rear-mounted RECTIFIER/BIAS switch lets the user select from the following three options:

Solid-state rectification with fixed bias (marked “S.S. AB2”). Listed at 60 Watts R.M.S.
Tube rectification with fixed bias (marked “AB2”). Listed at 50 Watts R.M.S.
Tube rectification with cathode bias (marked “A”). Listed at 30 Watts R.M.S.
Unlike many amplifiers marketed as “Class A”, the Prosonic truly functions as a Class A power amplifier in the “A” position. Class A refers to the amount of current flowing through the power tubes with zero audio signal, with Class A meaning maximum current flow even with zero signal. This makes the tubes run hotter, and gives the power section even more gain at the cost of tube life and noise. The Class-A designation for guitar amplifiers is often a misnomer; Few amps outside of the heralded Vox AC-30, also with cathode bias, operate in a true Class-A mode [Albeit, it only did so up to ~21 watts RMS]. While the Prosonic featured cathode bias in the Class A mode and fixed bias in the Class AB mode, not all class A tube amplifiers are cathode-biased, and not all fixed biased amplifiers are Class AB. Fixed bias amps, however, require lower B+ Voltages to stay within the Plate Dissipation of the power tubes used; Cathode biasing “throws away” this voltage using conventional Higher Voltage power supplies.

A channel-switching amp, the Prosonic offers a clean channel that features a blend of traditional Fender sounds with the influence of Vox amplifiers, frequently attributed to the Class A mode. Many players praise the Prosonic’s clean channel as being “softer,” and more prone to break-up and musically desirable distortion, than more contemporary Fender designs. Detractors view this trait as an apparent “darkness” in tone, and perceive this lack of the typical Fender “sparkle” as merely an undesirable lack of clean headroom.

The Prosonic also brought levels of gain (distortion) previously unavailable in a Fender amplifier. Taking a major cue from the first generation of Mesa Boogie amplifiers such as the Mark I (itself a modified Fender design), the Prosonic used additional gain stages in the preamp section that cascaded into one another. Although Fender had been designing amps with some facility for built-in distortion/overdrive since at least the late 1960s, never before had they arrived at a sound so readily usable for modern high-gain styles of music, and far removed from what many players consider to be archetypical Fender tones. The Prosonic’s factory manual states, “Gain 1 functions as a standard gain stage whereas Gain 2 functions similar to a compressor, adding sustain while reducing ‘edge’ when the volume is increased. This channel produces great high gain sound at any volume – from bedroom to stadium.”

Configurations and cosmetics[edit]
Prosonics were available first from the Fender Custom Shop, and later from Fender Musical Instruments, and for each production run, combo amplifiers featuring dual Celestion 10″ speakers, and head versions were available. (Zinky did make prototype combo versions with a single 12″ speaker). The circuitry is identical and offers users the sound similar to a louder Deluxe Reverb. The combo version featured a tube-driven, Accutronics spring reverb unit. The head version omitted the reverb tank.

While the vast majority of Prosonics were shipped with the standard black tolex covering, some of the initial Custom Shop run were finished in red and seafoam green pebbled tolex, called “lizard-skin” by Fender. Approximately 300 were made in red and 500 were made in seafoam green. The look of the amplifier borrows simultaneously from several eras of vintage Fender design: black “chicken-head” pointer knobs (as used on circa 1950s “tweed” amps), and the silver grill cloth, jewel lamp, and black control plate as used during the ‘black face’ period (mid-1960s). (Both models came with green jewel lamps).

Specifications and electronics[edit]
An all-tube design, the Prosonic uses standard 12AX7A tubes in the preamp sections, and one for the reverb send on the combo model. Output tubes are 5881/6L6WGCs. The rectifier tube is a 5AR4 (GZ34). The spring reverb unit in the combo model also uses a 12AT7 tube.

Although the Prosonic is a channel-switching amp, both channels share the same EQ section. Defying conventional logic, the Prosonic offers independent master volumes for each channel, or rather, on the clean channel, simply one volume control. The drive channel features the aforementioned dual cascading-gain controls, plus an additional master volume.

Two outputs for speaker cabinets are provided, (with switchable 4/8/16 ohm operation on the head version). The back panel also provides for a line-level effects loop, as well as an input for the channel-switching footswitch (the footswitch had a reverb button on combo models as well).

Discontinuation of the Prosonic[edit]
The Prosonic sold quite well, outselling the ’94 Twin (even though the Prosonic had a higher price and fewer features). However, overproduction of the amplifiers (due to the very good margin on the Prosonic) lead to overstock. This, factored with it remaining unchanged for 5 years (as new products get the most attention at music stores) led Fender to close out the Prosonic inventory and discontinue the product.

Towards the end of the 1990s, poor sales relegated many of the existing stock of Prosonics to closeout sale status. Theories abound as to why it was never a great success with players; foremost was its high price. It was simply perceived as too much money despite innovative design and glowing reviews. The Prosonic also suffered from something of an identity crisis; the cosmetics suggested classic Fender tones, and many players desiring an amp for Blues/Country playing, for example, were put off by the over-the-top lead channel. Conversely, the demographic for high-gain amplifiers, generally the domain of practitioners of heavy metal and the fledgling nu metal genre, and dominated by products from Marshall and Mesa Boogie, had long written off Fender as incapable of producing amplifiers catering to their style. The combo’s 10-inch speakers, though specially designed voiced for the Prosonic to handle huge amounts of power, were seen as too small by players favoring 12-inch speakers. The mechanical relay-based channel switching, designed to provide a more pure signal path, produced a large pop upon channel switching at low volumes, unlike other electronically buffered designs—this deliberate design choice was nonetheless perceived as the premier “design flaw” among players. Several of the Prosonic’s other quirkier design elements, such as the shared EQ and line-level effects loop, were designed for studio use and weren’t ideal for live playing. Understandably, buyers were attracted to the amp’s flexibility and, when used on-stage, these studio-friendly features were perceived as design flaws. Like with many other high-powered combo amplifiers, the Prosonic’s weight, at 60 lbs, was another less-than-popular characteristic.

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