Released in 1981, the Pro-One caused the industry some surprise, given that Sequential Circuits™(SCI) had been promoting their larger, more expensive polyphonic synths since 1978. I guess the Pro-One was SCI's attempt to bring the technology of the Prophet 5 and 10 to a wider market.

Introduced at the 1981 Winter NAMM Trade Show, the Pro-One is said to be the world's first synthesiser to sell for under $1,000. The original price tag was $645, but this increased to $745 and it is estimated that over 10,000 were made and sold.

Although the build quality of the synth has been criticised, its internal sound architecture is beyond reproach. Using the same VCOs, VCFs, VCAs and Envelope Generators as its bigger brother the Prophet 5, the Pro-One has endured the test of time as well as any of its Moog contemporaries.

What sets the Pro-One apart from other monosynths of its era is its somewhat complex modulation matrix. The simplest way to describe it (in one sentence) is that the oscillator frequency and pulse width and the filter cut-off can be modulated, either directly or using the wheel, by the filter envelope, LFO and/or Oscillator B.

The keyboard seems to bear the brunt of criticism levelled at the Pro-One. Later models (serial > 8500) have a particularly flaky membrane-type key mechanism. As the synth ages, the membrane contact degrades and can produce double-triggering or no trigger. The majority of Pro-Ones have a J-wire type key mechanism which is a more standard design and easier to repair when it wears out.

Another fault to look out for is the on-board power supply on models with serial <1500. The weight of the PSU makes the board vulnerable to damage when the Pro-One is accidentally knocked about. A number of the earlier models were returned to SCI and the PSU re-mounted on the chassis.

If you want to hear the Pro-One at its very best, have a listen to Upstair's At Eric's by Yaz, released in 1982.

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