What can I say? This thing's almost a monster. If the filters could be driven to self-oscillate (which they could be if it weren't for the operating system - they're analogue) then it would be just about the most incredible sounding synth around. It's a real chameleon, capable of shifting from clear, crisp digital textures to almost Minimoog-like basses and filter sweeps.
The architecture is pretty simple but with some complex twists. Once again, you've got three oscillators which are mixed after passing through three amplifiers in order to be filtered by a VCF. After this, the signal is passed through a final amplifier stage which also pans the sound to the outputs, which are stereo. Multiply this by seven and you have the ESQ-1.
There are a few extras, however. Modulation sources are drawn from a central "pool", which contains 3 LFOs and four envelopes which can be routed just about anywhere. Add to this the fact that the first two oscillators of any voice are not only syncable but also capable of amplitude modulation (which is a kind of multiplicative process which produces sideband frequencies which can range from bell-like harmonics to just plain ugly buzzes). You can also overdrive the oscillators into the filter, which is extremely handy for making the ESQ sound even more like a Minimoog.
All this and a solid MIDI implementation, too. Jonathan sold his ESQ-1 a while back and replaced it with the 2RU rackmount version, the ESQ-M. Not quite as easy to edit but, nonetheless, a very worthwhile piece of kit.