Archive of the former Yahoo!Groups mailing list: Discussion about the Korg PolySix synthesizer

Hi All,

In plugging my Polysix into my keyboard amp, I noticed a little tingle in my fingertips...like I was getting a mild electric shock. Weird.

So, with the Polysix and the keyboard amp both OFF, I used my multimeter to measure the voltage between the shell (ground) of the 1/4" audio cable coming from the polysix and the shell (ground) of the 1/4" audio input to my keyboard amp. It was showing 120VAC! (I live in the USA, where 120V is our mains voltage). Clearly, I did not feel that I received a full-blast shock from the mains power, so my problem isn't as bad as it might appear...though it still isn't good.

Still with the Polysix and keyboard amp off, I flipped around the polysix's 2-prong plug and (still off) did the voltage measurement again. It's now reading basically 0 VAC. Consulting the schematic, the polysix is grounding its chassis (and its transformer) through the "common" (aka "neutral") prong on the 2-prong plug. By flipping the the plug around, I'm connecting the chassis to either Mains neutral (which is maybe OK, but probably not) or to Mains hot (which is definitely not OK). So why am I not dead, but merely finger-tickled?

Flipping the plug back so that this ground-to-ground measurement showed 120VAC again, I connected a 2 kOhm resistor between the P6 and the keyboard amp. Measuring the voltage across the resistor, I got only ~1V, which means that I'm only delivering about 0.5 mA. So, while its troubling that I see 120VAC on the audio out, it is clearly a quite high impedance path from the Mains hot to the audio circuit's ground (based on these numbers, it's about 240 kOhm).

I'm assuming that I shouldn't be seeing 120VAC ∗at all∗. It just doesn't sound safe. Do any of your Polysix's show similar behavior?

Should I wap out the 2-prong (ungrounded) plug with 3-prong (grounded) plug so that I can tie all the grounds to earth ground?

Chip