The GRP Synthesizer A4 is an analogue synthesizer that is beautifully handcrafted in Italy, combining gorgeous workmanship with an insanely deep and powerful synthesis architecture. Derived from GRP’s previous flagship synthesizer A8, the A4 shares all of the same analogue sound generation and includes some new features that were previously not implemented on the larger A8, such as distortion on both of the filters and rich immersive ring modulation. The A4 is an incredibly deep and tonally complex synthesizer that packs in a stunning array of modulation capabilities, sequencing and routing options. Based around three wide range, multi-wave analogue oscillators, each with four dedicated modulation sources, sub octave generator on VCO 1 and 2, phase selection, and deep FM capabilities with linear and exponential options and FM 11 sources per oscillator. The VCO phase control let’s you build some seriously unique tones, especially handy for bass and leads where you want them to really sing through a mix, or even for drones in a similar frequency ranges, you can flip the phase and get a completely different result. Each VCO feeds into the mixer section, where you can dial in the levels of the three VCO’s, the two sub octave generators, bring in external inputs, control the noise levels and also control the depth of the ring modulation between VCO 2 and 3, or the external input should you chose. The mixer section then feeds into the two analogue filters, there’s a 24dB low pass filter with three slopes and a 12dB state variable filter with four modes. The filters can be used separately, in series or in parallel, giving you a wide variety of possible tones from classic Moog bass, smooth crisp Roland style sounds, SEM style voicing and so much more. As with the VCO section, there are an awful lot of modulation possibilities on the filter section. Including the aforementioned distortion per filter, which also serves as a level control per filter if you wish, multiple FM selections which can be derived from 11 switchable sources, the LFO’s or separately from the sequencer or even tracked from your keyboard or external MIDI device. GRP also included a very unique envelope generator into the A4, which provides the standard ADSR stages but also includes a hold stage, a level control for the sustain (not just a length control) with a user controllable gate length control and switchable response, so you can invert your envelopes should you wish to do so. Depth for both of the filters is hardwired, and each filter can have independent depths assigned to the EG. The next modulation source is the LFO’s and again these are less than standard. LFO 1 can be set to run freely, or it can be CV controlled by one of 11 sources. As with the VCO’s you can control the phase of LFO 1. You can also shape the LFO providing a slope to control the onset or decay of the LFO effect, shaping can be controlled by 11 different sources. The speed of the LFO can be sync’d to nothing (to run freely), gate, the sequencer or to MIDI clock. LFO 2 cannot be voltage controlled, but it has three ranges varying from super slow, to medium all the way into audio range and it has four hardwired send destinations including VCO, PWM, the filters and the VCA for AM and side-chaining effects. Next up is the Sample and Hold and Noise section, which has a glide control and can be clocked from either LFO’s or internal clock and can derive its voltages from 11 different sources. A4 includes white and pink noise sources. The A4 also supports external inputs and even has a dedicated envelope follower, with input gain control and a threshold control for triggering the envelope. And probably my favourite part of the A4 is the dual 8 step sequencer, which is loaded with features, such a variable clocking sources, variable time divisions and multiplications, they can even be chained together to make a 16 step sequencer and they can be quantized to fixed musical voltages or left as free running pitches for very interesting results. And if this amount of control wasn’t enough, well there’s a 25 point ¼” patch bay for making even more complex modulation chains. Great for integrating external signals or simply making new and unheard tones. The GRP A4 is pinnacle of subtractive synthesizer design, combining the very best of beautiful craftsmanship with a deep and rewarding synthesis tool kit. Not just a collectors piece, but a truly stunning instrument that is visually impressive and sonically impressive. The main features of the GRP Synthesizers A4 include Three oscillator analogue synthesizer Dual filters with distortion per channel Insanely deep modulation capabilities 25 point patch bay for even more modulation and connectivity Dual 8 step sequencers Advanced MIDI connectivity Lush, beautiful and rich sound Lovingly hand-built in Italy Exclusive in the UK to KMR Audio
