P4700 modular with two road cases. Courtesy of

modular synthesizer system sold by PAiA from 1971 until some time in the early 1980s. PAiA introduced this modular line to be a step up from the budget-priced 2720 series, with improved circuit designs and more flexible packaging, although it was still considerably less expensive than most competing products. Some of the 4700-series modules constituted notable improvement over the 2720 equivalents; for instance, the 4730 multimode VCF was regarded as a considerable step up from the non-resonant 2720-3 low pass VCF.

Unlike the 2720, the 4700 did not employ an all-in-one integrated base cabinet. A basic system consisted of a "road keyboard" enclosed in a wooden case, and at least one "road case" containing modules. Additional road cases could be added without limit, and road cases could be combined in pairs with a hinge and latch mechanism so that they could be folded shut for transport, protecting the modules inside. Each road case needed a power source, either a power supply module, or a power transfer module that took power from another case via a cable strung between the cases. The keyboard case was available without the keyboard installed; a user upgrading from a 2720 system could transfer the keyboard and interface circuitry from that unit into an empty 4700 keyboard case.

The 4700 used the same module formats, voltages and connectors as the 2720, so modules from both systems could be combined. Not all of the 2720 modules were duplicated in the 4700 line; for example; no noise source was ever made available in a 4700-series module, so a user who wanted that had to buy the equivalent 2720-5 module. To maintain compatibility, the 4700 VCOs and VCFs used Volts/Hz scaling, as did their 2720 equivalents. This made interfacing with other synths using Volts/Octave scaling difficult.

The 4700 series grew to have a large and involve user community, who created a newsletter and began exchanging ideas and designs for third-party and DIY modules. Quite a few 4700 systems grew to contain more user-built and third party modules than PAiA-designed modules. PAiA eventually stepped in to help publish the newsletter and expanded it into a full-blown magazine, which they named Polyphony. In the 1980s, when modular synthesis began to die off, PAiA sold the magazine to a publisher, where it morphed into the magazine now know as Electronic Musician.

In 1977, PAiA began offering, as an upgrade over the standard keyboard, a digital scanning keyboard which, when combined with the necessary support circuitry, was capable of supporting CV/gate outputs for up to four voics. The case had a slot to install the model 8700 single-board microcomputer, which provided the scanning function and could also be used for other purposes; the user also had to purchase a digital-to-analog converter and a quad sample and hold in order to obtain the four outputs. The DAC was an 8-bit type that had special output scaling circuitry on the analog side in order to properly drive the Volts/Hz scaled VCOs. Other software was available for the 8700 for use with the modular, such as a digital sequencer package.

There are more 4700 series modulars in existence today than there are 2720s, although both are rare and valued in the collector's market. There were some users who built some quite large 4700 systems, and a few of these still exist.

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