Would it be possible to hook up a piezo transducer (powered or not) under the springs in a strat trem, and use it as an onboard reverb? It'd be wonky but would it work with a loose trem and maybe 2 - 3 springs focused under one.
Spring reverb has much smaller, weaker springs. The trem springs are much too stiff. You could always try it out and see if you like it.
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