Does Behringer’s tribute edition measure up to one of the great monosynths of the 1980s, the Sequential Circuits Pro-One?
Initial skepticism about Behringer’s plans to bring out a whole series of reproductions of classic synthesizer designs—in parallel with their original designs like the DeepMind, Neutron, and Crave—has rapidly given way to delighted surprise, not only about the quality of the instruments, but also about the incredible price points the company is achieving. Certainly the secondhand market for original instruments like the Roland SH-101 and even the Minimoog Model D must have been affected by Behringer’s launch of highly convincing tribute editions of these instruments for a few hundred dollars.
Much like the Behringer Model D “Minimoog,” the PRO-1 is a slightly scaled-down reproduction of the control section on the classic Sequential Circuits Pro-One monophonic synthesizer. It omits the original’s 3-octave keyboard and adds MIDI In on a DIN connector.
You could remove this desktop-format module from its housing and mount it in a Eurorack case, if you prefer, where it would occupy 80HP of space. Because the MIDI input is on the front, it wouldn’t be lost in the process. A MIDI Thru jack and a USB connector are on the back panel, along with DIP switches to set the MIDI channel. With the Pro-1 mounted in a case, the small external power supply could be replaced by the Eurorack system’s power supply.
Go with the Flow
The panel design is very authentic down to every last detail of the typeface used, posing the question, how come this design is available for use? After Sequential folded in 1987, founder Dave Smith spent some years trading as Dave Smith Instruments before relaunching the Sequential brand in 2015. But it’s clear that the company currently has nothing in its catalog resembling the Pro-One, which was originally regarded as a single monophonic voice from their Prophet-5 keyboard, but without patch memory.
Whatever the position, it’s clear from Behringer’s recent trademark applications that many other instruments, including the Korg Mono/Poly, are also in their sights. The company’s policy always appeared to be to match the facilities of existing designs, then add a little extra and achieve a lower price. Looking at the PRO-1’s panel—which simply has every knob and switch from the original, plus additional minijack patching points, USB, and MIDI In and Thru—that’s certainly what they appear to have done.
The Pro-1 has a familiar signal flow. Two fully analog oscillators are based on the CEM3340-type chip. Each has a wide-ranging Frequency knob, 0–3-octave switching knob, Pulse Width knob, and simultaneously obtainable wave shapes—sawtooth and pulse for Oscillator A, plus triangle as well for Oscillator B. Oscillator A has a Sync switch for harmonic bending sounds, and Oscillator B has a Lo Freq switch for use as an LFO, together with the option of switching off Keyboard Control.
Below those are controls for the LFO, again with three simultaneously obtainable waveshapes. In addition to serving as a modulation source, the LFO clocks the adjacent sequencer and arpeggiator. You can record two sequences of up to 32 notes each in step time and then transpose those sequences from a connected keyboard. That’s a welcome technique that makes many familiar playing styles possible. Arpeggios are limited to either up or up/down patterns.
Like the original Pro-One, the Pro-1 has the incredibly useful ability to sync its sequencer and arpeggiator to a wide range of external audio signals. Not just clicks and clocks, but rough audio like a bass drum track works very well in this respect, making it easy to layer sequences. Although incoming audio signals are processed through the filter, you can vary the synth sound at the same time.
A Distinguished Panel
The Mixer section lets you control the volume of both oscillators, white noise, and external audio. Below that, the Glide section has a Rate control with Normal/Auto options, the latter working only when you play legato—holding down one note while playing another.
One of four Mode switches allows the PRO-1 to drone, bypassing the amplitude envelope—a terrific facility for creating continuous soundscapes, and one I’ve always missed in the Minimoog’s design. Another Mode switch plays repeated envelopes at the LFO/clock’s rate. Engaging the Poly switch means you can chain multiple PRO-1s (up to 16 units) for polyphonic playing.
The PRO-1 has two straightforward ADSR envelopes for the filter and amplifier. The 24dB-per-octave lowpass filter has the usual controls for cutoff and resonance, as well as knobs to control how much the envelope and keyboard tracking affect filter cutoff. To the filter’s right, the MIDI jack is just above
Above the front-panel controls is a row of 15 minijacks offering a wide range of patching opportunities. Alongside the gate/clock input and control-voltage inputs for a keyboard, oscillator frequency, LFO rate, and filter cutoff is one for controlling resonance—an option that never existed on the original Pro-One, despite the CEM3320 filter chip supporting that possibility. Another input accepts a control voltage from a modulation wheel.
In the same row of minijacks are CV outputs from the LFO and both envelope generators, as well as a gate output from the sequencer or arpeggiator. Audio connections on minijacks include a headphone output, external audio input, mixer output, and a mono main output handy for use in a Eurorack system.
The PRO-1’s Modulation section is located on the front panel’s left side. You can route signals from the filter envelope, second oscillator, or LFO to modulate filter cutoff as well as the frequency and pulse width of either VCO. Three knobs control the modulation amount, and switches allow you to either route modulation directly or control its depth with a mod wheel.
If this sounds like a complex and versatile set of options, it is. Keep in mind that Oscillator B can generate either audio or sub-audio frequencies. Using it as a modulator in the audio range results in clanging, metallic, ring modulator-like effects. In the sub-audio range, it can provide modulation at about the same frequencies as the LFO/clock, which may or may not be driving an arpeggio, sequence, or repeated gate at the same time.
Hearing Is Believing
Given the commendable inclusion of everything from the original plus the additional patching facilities, the question remains whether the PRO-1 sounds like the original. Of course it does, and very convincingly. I used the original Sequential Circuits Pro-One quite extensively when it was first released, and the new Pro-1 matches its sound in every aspect. The voltage-controlled oscillators use the same chip and sound strong, and the filter design is carefully matched to the sound of its namesake.
The typical Pro-One/PRO-1 sound is quite distinct from that of the Minimoog Model D or ARP Odyssey (also recently resurrected by Behringer). Perhaps the best way to describe the sound is a little smoother than the Moog or ARP, but it’s certainly more widely variable thanks to such extensive modulation options. What was typical of the Pro-One, accurately reproduced here, is what the filter does when you turn up the resonance. The filter can self-oscillate for whistling, abstract noise. Before reaching that point, though, the output loses a great deal of bass and volume. Although both have 4-pole 24dB-per-octave lowpass designs, the Minimoog’s filter response is quite different. The Pro-1 makes it easier to obtain thinner sounds with a reduced bass end, which may sit more comfortably in a mix.
With such a complete feature set, all that’s lacking are features that were also missing on the original. The PRO-1 has no filter options other than lowpass, no onboard memory, and no onboard effects—all options that undoubtedly would have increased the price. And although you can’t use the noise generator as a random modulation source, modulation can be extremely complex, especially when Oscillator B is in low-frequency mode.
With such versatile modulation capabilities, the PRO-1 (like the Sequential Circuits Pro-One) far exceeds the sound creation possibilities of the Behringer Model D (and the original Minimoog) with all sorts of repeated drones, modulated sequencing passages, clangorous metallic sounds, modulated white noise sweeps, lead or bass lines tailing off into subtle or extreme modulation, and much more. The original Pro-One’s contemporary Korg MS20 (and Behringer’s K2 clone) fall only slightly short of competing in this respect, though the Behringer Odyssey (and the original ARP Odyssey) manage to do so more closely thanks to a similar ability to use the second oscillator as a supplemental LFO.
As a lead-line and bass synth with all sorts of glide, repeated envelope trigger, and other options going on, the PRO-1 is outstanding. Again, it is quite versatile in offering some uncommon forms of modulation and expression. But it can cover plenty of other typically analog jobs too, such as making percussion sounds. Vince Clarke found the original Pro-One indispensable on the Yazoo albums and elsewhere, and synth-pop is only one of the many genres in which Behringer’s PRO-1 is certain to find favor.
An Old Friend Returns
It has been a pleasure to revisit the classic sounds of the Pro-One. As a desktop module, Behringer’s PRO-1 revives these sounds in a compact and highly affordable manner. The omission of the keyboard is no loss, as the original’s keyboard had problems with its delicate J-wire contacts bending and snapping. (In later versions, Sequential Circuits replaced the J-wires with rubber contact cells.) The PRO-1’s additional patch points and Eurorack mounting options massively extend the instrument’s sonic possibilities.
At $349, the modestly priced Behringer PRO-1 costs about one-quarter as much as a used Sequential Circuits Pro-One. Its construction feels sturdy, and I see no evidence that Behringer cut any corners in its construction. The new PRO-1 is sure to deliver the sounds of a classic analog synth to a whole new generation.