Sequential Circuits Pro One


Discovering hidden gems in the world of music production is always a delight, and one such gem is the Sequential Circuits Pro One. As an avid enthusiast of vintage synthesizers, I can attest to the Pro 1’s enduring appeal and its rightful place among the classiest monosynths in the second-hand market. Its timeless allure is not limited to my admiration alone; esteemed musicians such as Mark Kelly of Marillion and Vince Clarke of Erasure have also embraced the Pro 1, with Vince Clarke even crafting the bass drum for Yazoo’s “Only You” on this very instrument. So, let’s embark on a journey to unravel the wonders of the Sequential Circuits Pro One.

The Birth of Sequential Circuits Pro One

In the early 1980s, Sequential Circuits, renowned for their revolutionary Prophet 5 polyphonic synthesizer, introduced the Pro 1 to the world. At that time, the market was captivated by the allure of affordable polyphonic synthesizers, largely due to the success of the Prophet 5. One might question the need for another monosynth amidst the demand for polyphony. However, the Pro 1 managed to carve its own path by offering musicians an affordable gateway to the renowned “Prophet sound” without requiring them to part ways with their drummer’s car.

Features and Sonic Capabilities

The Sequential Circuits Pro One can be seen as a sibling to the Prophet 5, sharing many of its sound creation abilities. Some may label it as a “poor man’s Minimoog,” owing to its architecture that draws inspiration from the iconic Moog synthesizer. However, the Pro 1 possesses its distinct personality and sound. While expecting it to precisely mimic a Minimoog or TB303 would miss the point, the Pro 1 excels at delivering earth-shaking bass and ear-splitting shrieks while retaining its individuality.

Oscillators and Unique Composite Waveshapes

At the heart of the Pro 1 lie its oscillators, capable of producing sawtooth and square/pulse waveshapes. What sets it apart is the ability to combine these waves, generating captivating composite waveshapes that defy conventional expectations. Additionally, Oscillator B introduces a triangle wave, ideal for beefing up the low-end frequencies. Each oscillator can be independently tuned across four octaves, providing musical intervals that can be tailored to your desired tone. The Pro 1 also offers oscillator sync, enabling captivating sync-sweeps and aggressive lead sounds. Oscillator B doubles as a second LFO, often employed to introduce a sub-octave to complement the primary oscillator’s sound. This versatility expands the Pro 1’s sonic palette, offering a range of possibilities to explore.

Portamento and Enhanced Trigger Modes

The Pro 1 features a portamento function that adds smooth transitions between notes, controlled by a dedicated knob. A unique touch comes in the form of a switch that triggers the portamento effect when playing legato-style, allowing for seamless slides from one note to the next. This feature adds a layer of expressiveness and value to the Pro 1. Another noteworthy enhancement is the normal/retrig switch, revolutionizing keyboard triggering. While earlier monosynths required releasing all keys to retrigger envelopes, the Pro 1 fires envelopes with every new keypress, even when other keys are still held down. This advancement, made possible by microprocessor-controlled keyboard scanning pioneered in the Prophet 5, facilitates more fluid and versatile performances.

The LFO and Its Versatile Modulation Capabilities

The Pro 1 boasts a dedicated low-frequency oscillator (LFO) with sawtooth, triangle, and square waveshapes. These waveforms can be combined simultaneously, offering a multitude of composite waveshapes for experimentation. While an LFO speed indicator would have been beneficial, the Pro 1 compensates with a flexible modulation matrix. This matrix allows users to route modulation sources such as the LFO, filter envelope, and oscillator B to various destinations. The modulation amount from any source can be precisely controlled using a dedicated knob. The Pro 1 strikes a fine balance between flexibility and ease of use, opening up a world of possibilities for captivating modulation-driven sounds.

The Mixer Section and Resonant Filter

The Pro 1 incorporates a mixer section that enables users to balance the levels of oscillators A and B, as well as a white noise source. While some may miss the option for pink noise, the versatility offered by the noise volume control extends beyond adjusting noise levels. It also serves as the external input level control for the Pro 1’s filter and envelope sections. This opens up exciting opportunities for integrating external sounds and adding a layer of dynamic control through the filter cutoff. Additionally, the external input doubles as a gate threshold control, allowing external sounds to trigger the Pro 1’s envelope generators. Although finding the perfect balance between gate triggering and audio levels can be a challenge, the Pro 1’s overall flexibility compensates for this minor limitation.

The Pro 1’s filter, a straightforward low-pass design with resonance, is responsible for shaping the instrument’s character. While it may not possess the same aggressiveness as its Moog or ARP counterparts, it offers a distinct, bright, and distortion-free tone. Unlike the Moogs and ARPs, which tend to lose treble frequencies, the Pro 1 extends its range, delivering a glorious rasp of pin-sharp sawteeth. However, one minor drawback is the noticeable decline in bass frequencies when the resonance is turned up. Despite this limitation, the Pro 1 compensates by adding presence to the sound as resonance is judiciously introduced, making up for any perceived loss in low frequencies by adjusting the overall volume.

Envelope Generators and Percussive Potential

Both the filter and amplifier envelope generators on the Pro 1 provide full control over attack, decay, sustain, and release (ADSR). These fast envelopes enable the creation of percussive sounds with ease. Wood blocks, snares, bass drums, and other dynamic elements come to life effortlessly on the Pro 1. Additionally, the filter envelope can be routed to other destinations such as oscillator pitch or pulse width, expanding the sound design possibilities even further. The Pro 1’s envelopes, with their lightning-fast response times, add an exciting dimension to crafting rhythmic and percussive elements.

Unleashing the Magic: Modulation Section

The Pro 1’s true magic lies within its modulation section. In the early days of synthesizers, patching modules together with cables was the norm, allowing endless creative possibilities but often resulting in confusion and silence. The Pro 1 strikes a balance between flexibility and practicality by providing a modulation matrix that offers relative freedom while maintaining a logical and intuitive structure. The matrix takes inputs from the LFO, filter envelope, and oscillator B and routes them to destinations such as oscillator pitch, pulse width, and filter cutoff. The modulation sources can be routed directly or through the modulation wheel, granting users precise control over the modulation amount. These modulation capabilities, once mastered, unlock some of the most thrilling and unique sounds achievable with an analog synthesizer.

Unleashing Creativity: Arpeggiator and Sequencer

The Pro 1 features an arpeggiator and a 40-note sequencer that enhance its creative potential. However, both rely on the LFO as their internal clock source, limiting the LFO’s availability for modulation unless an external clock is utilized. The arpeggiator allows users to scan the keyboard in an upward or up/down direction, while a latching function retains the last notes played, adding new notes as long as they are held. While this feature offers creative possibilities, it may not find universal use among all musicians. The sequencer, while basic in design, serves as a source of inspiration. Experimentation with note placement and random gaps can yield interesting and evolving patterns. It’s important to note that the Pro 1 does not possess built-in memory for saving sequences, requiring manual transcriptions or the use of digital note-taking tools.

Integration and Connectivity

For seamless integration into modern setups, the Pro 1 can be connected to MIDI to CV converters. This opens up a world of possibilities, as the Pro 1 can be controlled and played via MIDI. Utilizing CV and gate leads and setting the trigger mode to external, users can achieve synchronization and real-time transposition. The Pro 1’s filter can even be modulated by velocity or the mod wheel, further expanding its expressive capabilities. Whether triggering the Pro 1 with external instruments or utilizing it as a MIDI-controlled noise gate during mixdown, the Pro 1’s connectivity options empower musicians with endless creative opportunities. The tactile nature of its knobs and switches enhances the overall experience, putting creative control at your fingertips.

Reliability Concerns and Maintenance

While the Pro 1 offers exceptional sound and features, it’s important to address reliability concerns. Some users have reported frequent breakdowns, indicating potential issues with long-term stability. The most notorious problem is the double triggering keyboard, which tends to manifest as the synth ages. However, rectifying this issue is relatively straightforward, requiring a simple adjustment of the keyboard mounting. Another common complaint pertains to crackling knobs and switches. The severity of this issue varies among individual units and may require cleaning or component replacement. Additionally, the Pro 1 may exhibit acoustic hum from the transformer, although this does not affect the audio circuits. While these concerns exist, proper care, maintenance, and sourcing components from electronic suppliers can help mitigate these issues and ensure the longevity of the instrument.

Output Level and Considerations

One aspect to consider when working with the Pro 1 is its high output level. Compared to other synthesizers in my studio, the Pro 1 generates a hotter signal. While this can be advantageous, it necessitates careful handling to prevent overdriving subsequent equipment in the signal chain.

The Behringer Pro-1

The Behringer Pro-1, a modern reincarnation of the iconic Sequential Circuits Pro One, strikes a balance between preserving the past and embracing the future. Like its predecessor, the Pro-1 is a monophonic, dual-oscillator synthesizer, known for its all-analog signal path. It faithfully reproduces the raw, powerful sounds that made the Sequential Pro-One a classic. However, the similarities don’t end there. The Pro-1 also features a 3340 VCO and a 24dB ladder filter, elements that were key to the original’s unique sonic character.

Yet, the Behringer Pro-1 isn’t just a carbon copy of the past. It introduces modern features that extend its capabilities beyond those of the original Pro-One. A prime example is the modulation matrix, which opens up a vast landscape of sound design possibilities. Additionally, the Pro-1 comes equipped with a step sequencer and arpeggiator, tools that enhance its versatility and performance potential.

In terms of form factor, the Pro-1 is more compact and portable than the original, making it a convenient choice for today’s mobile producers. Despite its smaller size, it doesn’t compromise on build quality or sound fidelity. In terms of price, the Behringer Pro-1 is significantly more affordable, making the iconic Pro-One sound accessible to a wider audience.

In conclusion, the Behringer Pro-1 pays homage to the Sequential Pro-One, replicating its signature sounds and features while introducing modern enhancements. It’s a testament to how far synthesizer technology has come, offering a blend of vintage charm and contemporary functionality.


The Sequential Circuits Pro One remains a highly desirable monosynth, cherished for its distinct sound and timeless appeal. Its affordability and unique sonic character make it a valuable addition to any music production setup. From its versatile oscillators and composite waveshapes to its enchanting modulation capabilities, the Pro 1 offers a world of sonic exploration. It excels at delivering earth-shaking bass, searing lead sounds, and captivating sequenced riffs. While reliability concerns and minor drawbacks exist, such as the double triggering keyboard and crackling knobs, they can be addressed with proper care and maintenance. Overall, the Pro 1 continues to captivate musicians with its distinctive sound and exceptional performance capabilities.


  1. Can the Sequential Circuits Pro 1 function as a polyphonic synthesizer?
    • No, the Pro 1 is a monosynth, designed to produce one voice at a time.
  2. How can I resolve crackling knobs and switches on the Pro 1?
    • Cleaning the contacts of affected knobs and switches is the recommended approach. If the issue persists, replacement components may be necessary.
  3. Is the Pro 1 suitable for creating percussive sounds?
    • Absolutely! The Pro 1’s fast envelope times make it well-suited for generating percussive sounds such as wood blocks, snares, and bass drums.
  4. Can I save my sequences on the Pro 1?
    • No, the Pro 1 does not feature built-in memory for saving sequences. However, manual transcriptions or digital note-taking tools can be used to preserve your sequences.
  5. What are some alternatives to the Sequential Circuits Pro One?
    • Other monosynths in a similar price range include the Korg MS-20, Moog Minitaur, and Arturia MiniBrute. Each synthesizer offers its unique features and sonic character.