Dating polytone amps
The cards are labeled as version "A." The published Roland documentation supports version "B: and "C." These rare "A" cards are unusual in several ways: the component layout is very different and the outputs trimmers seem to be arbitrarily placed on the board.You can also see jumper wires soldered across the board.Like the GR-300, there are three versions of the G-303 and G-808 guitars, distinguished by changes to the PC board.I was contacted by a G-303 player in the States and a G-808 player in Norway both using the first run, early "prerelease" version of the guitar electronics.If there is one guitar that has become the "gold standard" of guitar synthesizers, it has to be the Roland G-303 guitar.No doubt much of the popularity of the G-303 comes from Pat Metheny, who has played this guitar year after year on stages across the world, always amazing audiences with the moving and emotional quality of the G-303 and GR-300 rig.
IC4, IC5 and IC6 op-amps are used to create the hex fuzz sound. The line-level amplifiers are surrounded by resistors for a simple gain circuit, and the hex fuzz amplifiers have the network of diodes used to create the fuzz sound.
The pin out information was correct on the G-505 Service Manual Schematics schematic, which uses almost the same circuits.
All the G-303s and G-808s that I have checked have op-amp pin outs consistent with the G-505.
From looking at the version "A" photo, it appears the one op-amp is used per string to both amplify the signal and create the hex fuzz sound.
If you look at IC6, at the top of the version "B" and "C" card, you can see resistors just to the left of the chip creating gain in the negative feedback loop, and additional diodes just to the right side of the chip for generating fuzz. After years of working with Roland vintage electronics, I finally noticed that there were two variations on the familiar hex pickup.
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When switching from the 80 ohm (narrow) to 900 ohm (wide) pickup, there is a 10:1 increase in impedance, likewise, it is necessary to change the negative feedback loop resistor by a similar ratio, from 330K to 33K, and from 1 M to 100K.