Listen to the Deep Holes
JLCPCB Prototype for $2(Any Color): https://jlcpcb.com
How to Get PCB Cash Coupon: https://bit.ly/2GMCH9w
An ambitious attempt to hear the effect of phase cancellation by adjacent multiple feedback bandpass filters summed together in a mixer circuit. Exploding capacitors didn't help.
ETI Vocoder constructional project reproduced with kind permission of Wimborne Publishing Ltd. http://www.epemag.com
Update: I fitted all 16 tantalum capacitors (on the proto boards) the wrong way round :/