I’m building a frequency-voltage converter transformer for my vintage Lenco turntable. I’ve done a proof of concept using an 120ac to 12v dc transformer hooked to a 12vdc to 230v 50hz inverter. It worked, but the inverter creates a modified sine wave and a pure sine will be better for the motor. I’ve assembled a new converter/transformer using an LED driver and a pure sine wave inverter which takes care of frequency-voltage conversion ver well. It also creates an horrible noise in the speakers. My test setups made no noise. Here’s the difference: for the new converter I took the electronics out of the aluminum case and mounted them with the driver in a plastic Hammond case. Is this a shielding problem?