ARP Solus, courtesy of Amazona.de
A monophonic analog synthesizer introduced by ARP in 1980. Lightweight and built into a road case, with a 37-key keyboard and a very compact panel layout, the Solus was intended for portability and quick setup. As far as its voice architecture, it was midway between the Axxe and Odyssey; to the Axxe architecture it added a second VCO, and a ring modulator circuit. The VCF was a new design, which was never used in any other ARP model, and was better regarded by performers than the venerable 4075. An external input allowed a external source to frequency modulate VCO 2; another allowed an external source to be fed to the ring modulator. The only performance control besides the non-aftertouch or velocity keyboard, was a simple non-sprung knob for a pitch wheel, in the style of the Mark I Odyssey, in place of the PPC controls used on other ARP models of the era.
The Solus has a rather complete CV/gate interface. Both inputs and outputs are provided for control voltage, gate and trigger signals. An interesting feature of the control voltage output is that it captures the combined control voltage that is fed to VCO 1, which means it includes all of the applied modulations, including the pitch knob and LFO signal, rather than just the keyboard voltage.
The Solus remained in production less than a year. It had the misfortune of being introduced as ARP was on its last legs financially, and production of the Solus (along with all other ARP models) ceased wen the company went out of business in 1981. It appears that only a few hundred were produced, and it remains a little-known model even among many ARP collectors.