Sequential Circuits Inc.


Updated: 2004-02-18

Many consider the Sequential Circuits the best monosynths of all times. That may not be entirely true; but it sure is a mean bastard even compared to the other classic beasts of the analogue monosynth world!

What's the big thing then? It has the standard stuff you'd expect from a good monosynth, double VCO's and VCF, good interfacing possibilities and a decent sequencer and arpeggio.

The cool thing about the Pro-One is the flexiblity. The routing section on the left offer many weird choices as you let the signals modulate eachother and get the most wicked results. I didn't say useful, I said wicked and that is often the problem with the Pro-One. How to use those weird sounds... ;)

The physical appearance of the Pro-One is nice, large knobs, wooden end cheeks, good layout but all that is just cosmetics. The building quality is in fact quite poor with plastic where the big brother, the Prophet 5, had wood or metal. The wood barely passes as wood and the keyboard... that's the favourite hate object of the Pro-One.

I'm a lucky owner of a working example, but most Pro-Ones suffer from glitches and double triggering if any at all. Who cares if you run it over cv/gate anyway? It also has one of the ugliest logos around if you ask me... 

I bought mine in mint condition from a bass player and I have a synth made in the middle of the production line. Circa 10000 were made and mine is in the 5000's. On my last page I wrote; "I guess that means I have a fairly good keyboard, but most certainly my PSU is mounted on the circuitboard *yerk*." When making this upgrade I opened the little wicked thingy and found out a lot of things.

The PSU is safely screwed to the bottom. My Pro-One is originally sold here in Sweden and therefor there's no 220/110-voltsswitch and the PSU is a swedish thing too. The serial number on the back doesn't correspond to the numbers inside. It would be cool to know if your Pro-One is like that too or if mine have had it's interior exchanged at some time in the history. A part of the history was exposed when I found parts of packing material inside.

I even took off all the knobs to take some shots at the legendary "hippiestuff" on the circuit board. Here's what I found on mine. The mantra (om mani padme hum) is there in the top left corner, as is the meditating buddha (between two envelope knobs and since my Pro-One is a rev 1.2 I also have the mushrooms there. It would be fun to know what SCI thought of (or smoked?!) when doing this!

The board is signed and there are scribbled notes both here and there...

It sure is one of the most common monosynths, but it still changes owner at quite high prices.

My daughter digs the Pro-One too!

SCI Pro-One specifications;
Keyboard  37 keys, 3 octaves
Oscillators 2, one with ramp & square (incl. pulsewidth), one with ramp,
triangle & square (incl. pulsewidth).
Filter Lowpass (24 dB?) with adjustable envelope and keyboard amount controls + dedicated envelope.
Envelopes two ADSR's (one for the filter)
LFO ramp, triangle & square (simultanously? How does that affect the shape?!).
Sequencer 2 sequences with a maximum of 40 notes together.
Connections audio out, audio in, filter cv in, gate out, cv out, gate clk in, cv in
Housing wood, steel & plastic
Dimensions 653 x 417 x 130 mm
Weight approx. 7 kg
Released 1981
Quantity produced
approx. 10000
Pros Good sounds, very flexible without patchcords, considered a real classic.
Cons Too classic? Easy to get stuck in the "typical" sounds and imitating Vince Clarke ;) Quite pricey these days (at least in Europe). Bandpass filter would be a nice addition!
Price? (bargain,
fair, horrible)
$500, 800, 1100

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