GRP A1 – name it Dr. BASSSSSSSSssssssss

… or Dr. Elegiac-Solo-Voice, come to think of it. The magic words: sub-oscillator and triangle wave. Besides great basses and elegiac voices, the GRP A1 also brings FX sounds (moderately, of course) and gorgeous sequencing sounds / performances. Its very special feature, reminiscent of Roland’s immortal TB-303, is the 18 dB VCF with Distortion. Actually – surprise! – the handy GRP A1 turns out to be more of a studio synthesizer than just a little addition to your live gig bag.

GRP A1 Synthesizer

Be careful when unpacking …

Not really huge (and by no means a Goliath), the GRP A1 arrives solidly packaged. But be careful. Wild handling is not recommended, since the synthesizer has metal side panels with unexpectedly sharp edges. So, be careful when unpacking the A1.

Once the A1 is out of its packaging, you will notice there is no power adapter. The included USB lightning cable enables the synth to be powered from a Mac or PC, of course. But if you wanna use the A1 as stand-alone synth, a corresponding 2.5A (USB) PSU should be handy in you pockets. This was not true in our the case, but after a quick order the matter was checked off: “solved”.

GRP A1 Synthesizer

Desktop synthesizer and Eurorack module in one package

The concept of the GRP A1, a square desktop analog synthesizer with a single VCO, is not new. Way back in 2009, Doepfer launched the DARK ENERGY, an extremely successful synth which received many awards. It remained in production as DE II or DE III until 2022.

In keeping with their own Eurorack tradition, Doepfer also launched the DARK ENERGY in the form of the A-111-5 Synthesizer Voice. Thanks to the new AS3394 chip, this A-100 Eurorack module is still available today – either as a standard edition or as a vintage edition.

GRP A1 Synthesizer

GRP has now implemented a very similar synthesizer concept, whereby the Italian company has combined both systems in one unit. So you can use the GRP A1 as a desktop instrument (as delivered), or remove the synthesizer part and screw the module in your Eurorack modular system.

The process of transformation is simply exemplary. Remove 4 screws, loosen the A1 front panel and two ribbon cables – and the GRP A1 becomes an Eurorack module with standardized bus connections …

GRP A1 Synthesizer


The functions of the GRP A1 are quickly listed:

  • 1 VCO with pulse (PWM), triangle and sawtooth; Osc-FM
  • 1 sub-oscillator (also with PWM)
  • Noise generator
  • 1 ADSR envelope
  • 1 18dB VCF with DISTORTION; Filter-FM
  • 1 VCA with ADSR, HOLD or Gate mode
  • 2 LFOs with sawtooth, triangle, pulse, S/H and SHAPER

GRP A1 Synthesizer

  • MIDI-IN and various CV connectors
  • MIDI: Note On/Off, VEL, Pitch-Bend
  • Audio-Out, Phones, Audio-In (!)
  • Portamento (Glide)

What you find in the A1 is – not entirely surprising – a conglomerate of various GRP products, a mixture of the GRP A2 and the GRP Eurorack modules. Specifically: The MIDI glide bend section is reminiscent of the A2 (or A4). The oscillator comes from the GRP Eurorack module VCO, the two LFOs seem to come from the DUAL LFO module (here with addition of sample / hold), just as the envelope might be a direct offshoot of the Eurorack ADSR module.

GRP A1 Synthesizer

Finally, the filter is a modification of the GRP module 24 dB LOW PASS, here in the selective 3-pole version with 18 dB slope. And Voilà – here’s the concentrated version of all of this, the A1 as THE compact GRP synthesizer voice. It doesn’t get any smaller, that’s for sure!

By the way: If you already own a GRP Eurorack system, you actually have the sound and functions of the GRP A1 at hand. Admittedly at higher costs and with higher space requirements, but also with extended musical possibilities, which is, of course, in the nature of a modular system.

GRP A1 Synthesizer

Live synthesizer or studio synthesizer?

Considering its cute size, one might jump to the conclusion that the A1 is the perfect live-instrument. Well, this would be true if there weren’t some hitches.

Hitch 1: The ultra-compact synth design. Those compact knobs and tiny switches can be tricky to get to, especially when using patch cables. And even without patch cables, pointy fingers would really come in handy for setting the appropriate decay time, FM intensity, LFO rate etc.

GRP A1 Synthesizer

Hitch 2: The relatively tricky TUNE control. This allows the overall sound to be shifted by +/- one octave. Fact: There is no zero point in the center. When deviating from that center, it is difficult to find back to the exact basic tuning. In the studio this doesn’t matter (there you have time), but live ?

Hitch 3: The stunning dynamic vistas. Just a few millimeters on the control settings EG AMT, VCO LEVEL, MAIN OUT can shoot you from “barely audible” to “suddenly too loud” (or vice versa). Again: In the studio no problem (there, one is grateful for the large dynamic range), but live ?

GRP A1 Synthesizer

First and foremost, we thus consider the GRP A1 to be a formidable studio synthesizer. In the studio, exact adjustment and adaptation can be done at leisure. In the studio, the GRP A1 unfolds its true sonic potential. And in our studio, this small synthesizer well enhances the veteran (analog and digital) instrument group.

Pulsating BASSSSSSSSsssssssses, elegiac flutes, strong FM effects

As to enhancement: The A1’s very special bass makes the difference. The A1’s very special flute voice breaks the ice. Vibrant A1 FM effects and sequencing entities enliven the studio. So, in many situations, the small GRP synthesizer contributes very special aspects to the overall musical picture.

GRP A1 Synthesizer

Examples? MIX – V-Synth 1: Smooth digital pads and that one creaky A1 BASSSSSSSSssssssss, a perfect fit. The rather “flat” pads become immediately powerful, emerging an unexpected multi-layered character. MIX – CP70B 2Piano solo and that one heartfelt A1 flute voice: emotional outbursts echoing through the studio. MIX – COTK 55: Modular sequencing and, as an encore, that one A1 KEY VEL FEG solo lead line: dynamics, pressure and “punch” increase, the temperature in the studio rising.

Hey, and by the way, another very productive field of application the GRP A1 is the processing external music (Audio In): The GRP as a filter box!

GRP A1 Synthesizer

Moving away from the excellent complementary qualities of the GRP A1 (in sound combination with other instruments), we come to an evaluation of the instrument as a pure solo synthesizer. This we see as really very good, but not as excellent.

Very good: sequencing in both the bass and upper ranges (thanks to the powerful sub oscillator, the crunch filter and the fast envelope). Very good: lead sounds in bass, middle and especially in treble ranges (thanks to the powerful VCO, the triangle wave as a distinctive timbre, the colourful 18 dB filter, the flexible envelope with release times up to 40 seconds possible). Very good: effect sounds (thanks to noise, VCO-FM, VCF-FM, the two LFOs with S/H and SHAPE, as well as the CV inputs for controlling filter and amplifier).

GRP A1 Synthesizer A few rough edges

LFO frequency range can only be switched from SLOW to MID via HIGH mode. Continuous increase of the LFO speed from 0.1 Hz to 2.4 kHz is not possible. And the LFO triangle wave with SHAPE position left (or right) doesn’t really produce an authentic sawtooth waveform. Which means that – especially audible at low LFO speed – SAW misses its characteristic sharp edge, it’s simply not a true sawtooth waveform. Which you can hear.

The tricky center position of TUNE has already been mentioned (see hitch 2 above). Since the GRP A1 pots react very precisely, one needs a lot of sensitivity to find the way back to the original A1 tuning once the TUNE pot has been moved. The result may not be satisfactory without multiple readjustment, and, possibly, comparison with other instruments.

GRP A1 Synthesizer

The VCA may be a bit noisy, depending on the sound setting. Simple solution: Turn MAIN OUT back to its center position – noise-free zone! And yes, KEY VEL FEG (the effect of the velocity on the filter envelope) tends to overreact.  Dynamic contrasts, which can be enormous, may be difficult to limit. It might need some practice to find the right balance between your own playing and the resulting velocity effects without torn-off pianissimo notes or unwanted fortissimo accents.

This only as an addition, so that no rogue thinks “oh, that-was-not-mentioned” or “oh, the-written-is-only-embellishment”. Not at all. A great instrument with a few rough edges.

GRP A1 Synthesizer

The SOUND speaks for itself

Now to the essence. The SOUND speaks for itself. Leave all details aside and make room for 40+ minutes of GRP A1 music (found in the appendix). Tech talk fades away completely as the creaky GRP bass enlivens the room. Or when the A1 VCO unleashes its power with that lyrical triangle waveform. When demonic or lovely sequences move the mind. Each must judge for himself. In our opinion, the audio quality of the GRP A1 is impressive, and notably unusual for a synthesizer of this size. And be warned (in a positive sense): Its uniquely wide frequency range could re-describe your own pain threshold in the high-end audio ranges.

Nevertheless, a note for all those who associate GRP with the “big machines”. The GRP A1 is certainly no A2, it’s no A4 and no A8 … how could it be? It neither offers multiple oscillators, nor that famous GRP MultiMode VCF (and many more extras).

GRP A1 Synthesizer

One therefore does well to recognize the A1 for what it is: A compact, stand-alone desktop / Eurorack synthesizer with 18dB (303) filter, a doctor for great basses and elegcias voices …


The GRP A1 – with 17 x 13 cm certainly not a huge instrument – has the potential to be a huge sonic factor in the studio. Its musical potential may be limited, due to the singular VCO and the singular envelope, but what the A1 produces acoustically is still enormous. Notable, the 18 dB filter, which delivers (with or without distortion) wonderfully creaky sounds. A single GRP A1 filter sweep can have the studio shaking while adding the necessary warmth and pressure to many an atmosphere in your mix.

GRP A1 Synthesizer

As to the plain VCO, the triangle wave (TRI) – besides those classic waveforms sawtooth and pulse – is a distinguishing feature. Triangle is a real gem, an insider tip, essentially a “novel” sound source. Soft and surprisingly powerful at the same time. We emphasize: GRP A1 triangle solo voices can be transcendental.

Furthermore, in the FX area, two LFOs (up to 2.4 kHz) along with various FM options yield generous sound potential. And finally – it’s so self-evident that we almost consider the remark dispensable – the GRP A1 is an excellent, and outstandingly performable, sequencing synthesizer.

A distingishing basic musical feature is the instrument’s wide audio range. Not only the obligatory basses, also the highest trebles astonish the listener.

GRP A1 Synthesizer

To sum it up: The GRP A1 cuts a fine figure, whether as a desktop synthesizer or Eurorack module (the conversion from the one to the other only takes a few moments). At 599 USD / 585 Euros it may seem be a bit pricey, but this is a true GRP synthesizer, meaning true quality, true hardware and unusually true sound.

Attached: 40+ minutes of audio material, including (besides the GRP A1 synthesizer) the Roland V-Synth, COTK Model 55 and Yamaha CP-70B. Single and multitrack recording (e.g., for stereo GRP A1 sound impressions) in Audacity.

GRP A1 Desktop Synthesizer / Eurorack Module

Monophonic analog synthesizer

1 VCO, Sub-Osc, 1 VCF, 1 ADSR, 1 VCA, 2 LFOs
MIDI, CV/Gate and various patch points

Eurorack size: 16,3 cm width (32HP)

approx. 599 USD / 585 Euros


Open / Download:
GRP A1 Synthesizer photo 1 (4000 x 2600 px)
GRP A1 Synthesizer photo 2 (4000 x 2600 px)

Compare with:
GRP Eurorack Review
GRP A2 Review
GRP A4 Review
GRP A8 Review

Youtube Video:
GRP A1 demo (by Schneiders Laden)

GRP A1 Synthesizer

Filed under 2023, Featured, Main Feature, Reviews

“Es genügt, einen Ton schön zu spielen” sagte der Komponist Arvo Pärt im Jahre 2005. Diese Aussage ist ebenso einfach wie ich auch exzellent: Es braucht kein Meer an Tönen, denn entscheidend ist der Klang. Dass so mancher Vintage-Synthesizer der 70er und 80er Jahre teils unerreicht hochwertige Klänge liefert, steht außer Frage. Doch tatsächlich leben wir “heute” in einer nahezu perfekten Zeit. Einerseits hat man – mehr oder weniger – noch Zugriff auf die Vintage Analogen, andererseits wird auch bei Neugeräten die wichtige Komponente des hochwertigen Klanges wieder zunehmend berücksichtigt. Doepfer, Cwejman,, MacBeth, Moog, GRP, Studio Electronics, COTK, John Bowen und andere Hersteller bauen hervorragende Synthesizer, die den “Klassikern” in nichts nachstehen. All diesen (alten wie neuen) “großartigen” Instrumenten ist Great Synthesizers gewidmet. _________________________________________________________ In 2005 composer Arvo Pärt said: “Playing one tone really well is enough”. In other words, it is sufficient to play one tone 'beautifully'. I agree with that. All musical efforts are focused on the sound itself. Although I studied classical music (piano and drums), it’s the electronic sound that inspires me. Synthesizers are the epitome of new sounds and exciting tonal spheres. Today, many companies produce high-quality - excellent! - synthesizers: Doepfer, Cwejman, MacBeth, Moog, GRP,, COTK, Studio Electronics, John Bowen and others. It's their products I'm really interested in ... apart from Vintage Synthesizers, which I have been collecting for 20 years. Subsequent to our former websites Bluesynths and Blogasys, Peter Mahr and I have now created GreatSynthesizers. We hope you like it.

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.