BOSS SY-300 Guitar / Bass Synthesiser. Although I am sure you know what you are looking at, but just in case, this is one of Boss's guitar synthesisers that don't need a separate special pickup and just work on the normal signal of a guitar applying a set of filters and oscillators driven by the input signal, giving an instant response to the signal, works with notes from the top of the guitar to the bottom of the bass.
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