Moog’s incredibly popular Sub Phatty is an excellent option for those on a (slightly) lower budget, but the newer Sub 37 justifies its higher price with a much more comprehensive feature set.
The Sub 37 is based on the Sub Phatty sound engine, so you can expect a slightly dirtier take on the classic Moog sound, but the end result is something quite different to the Phatty, way beyond the fact that you get a 37 keys as opposed to the Phatty’s 25. For a start there’s a third oscillator. And a second LFO. Plus there’s a sequencer. Oh, and it’s got a duophonic mode. Clearly, this is a big step up.
The Sub 37 is also easier to program than the Sub Phatty thanks to a more comprehensive array of front-panel controls. That means the overall experience is much closer to using a vintage one-knob-per-function synth than you’d get with the Sub Phatty.
If all of this sounds more like a criticism of the Phatty than praise for the 37, don’t take it the wrong way; the Sub Phatty is still a great synth, the 37 is just even better.