GRP Synthesizers built the A4 as a more compact and affordable alternative to their flagship A8, but don't mistake "smaller" for "less capable" — this Italian-made beast packs three oscillators, dual filters, and enough modulation routing to keep you exploring sounds for years.
The heart of the A4 is its three voltage-controlled oscillators, each with four dedicated modulation sources, sub-octave generators on the first two, and deep FM capabilities with eleven modulation sources per oscillator. The signal path splits into two parallel analog filters: a 24dB-per-octave transistor ladder lowpass with three slope options and a 12dB-per-octave state-variable filter offering four modes. Both filters include integrated distortion and can run separately, in series, or in parallel, letting you dial in everything from classic Moog-style bass to crisp Roland-like tones. The A4 includes a ring modulator, white and pink noise, an envelope follower for external audio processing, and a dedicated autopan section that adds movement to your patches. Two envelope generators provide standard ADSR control plus a unique hold stage and inverted response options, while two LFOs and a sample-and-hold circuit round out the modulation toolkit. The built-in 8x2 and 16x1 step sequencer handles complex sequences and generative patterns, with support for step repeat, permutations, and multiple directions. MIDI connectivity includes note messages, pitch bend, modulation CC, velocity, and aftertouch, plus CV/gate I/O for external control.
The A4 measures 815 by 455 by 252 millimeters and weighs 20 kilograms, sitting comfortably on a desk or stand without dominating the room. Its front panel uses click-stopped switches for routing rather than patch cables, which trades some immediacy for clarity and repeatability. Community feedback highlights the synthesizer's sonic depth and modulation flexibility, though some users note the interface requires time to master and wish for pitch-bend control over filter frequency. Hand-built in Italy with a wood cabinet, the A4 has earned respect as a serious instrument that rewards deep exploration.
