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

Ha, just stumbled upon this again while looking for posts on reducing noise.

It's a simple thing to just plug the two-prong jack the other way by flipping it 180 degrees - doesn't matter if it is soldered or not at the Polysix side, of course.

Actually, I did this for my DAC's PSU that I built myself, and one of the two ways provides mch better sound. The orientation probably shows differing levels of leakage currents.

You can do that for any audio equipment with two prongs, provided the two prongs are both small enough in Northern America as one slit is smaller - at least that's how it is in Canada.

that is a signal there is something wrong with the psu. maybe not from
the dac, but one of the many things in your signal path. I would worry
if the orientation of the prong changed your sound... psu's should be
isolated from the mains.

On 06-04-18 00:03, josh.nursing@gmail.com [PolySix] wrote:
> Ha, just stumbled upon this again while looking for posts on reducing noise.
>
> It's a simple thing to just plug the two-prong jack the other way by
> flipping it 180 degrees - doesn't matter if it is soldered or not at the
> Polysix side, of course.
>
> Actually, I did this for my DAC's PSU that I built myself, and one of
> the two ways provides mch better sound. The orientation probably shows
> differing levels of leakage currents.
>
> You can do that for any audio equipment with two prongs, provided the
> two prongs are both small enough in Northern America as one slit is
> smaller - at least that's how it is in Canada.
>
>

--
Met vriendelijke Groet,

Simon Claessen
drukknop.nl

More information about what Chip and many others with various equipment (but it is especially known by audiophile types) have found:

https://www.gcaudio.com/tips-tricks/determining-proper-ac-polarity/

Yash

None of my previous posts or replies appear at all.

Understand that this happens with all PSUs.

Here's another piece of information about AC Polarity (from https://forum.audiogon.com/discussions/ac-cord-polarity-does-it-matter). It is worthwhile to do that with all audio equipment to ensure you get the best SQ (sound quality):

"Instructions from the Chesky website:

By Michael Trei
One simple tweak that many people tend to ignore, is to be sure that each piece of gear is plugged into the power outlet using the proper polarity. The power supply transformer in every piece of gear will leak a little current to the component's chassis, and in most cases, you'll get better sound if this leakage is minimized by observing the proper A/C plug orientation.

A few decades ago, audio gear had simple two prong A/C plugs that could be inserted in the socket either way, but now all plugs are polarized so that they only go in one way. To get around this, we need to use a simple adapter called a cheater plug, available for a buck or so at any hardware store. The cheater has two narrow prongs that allow you to use it in the socket either way, and cheaters will also take a three prong plug with a ground pin, replacing the ground prong with a metal tab or wire that you can connect to the center screw on the outlet plate. If you want to reverse a three prong plug, you'll want the version that uses a wire so that you can still connect the ground with the plug in the reversed position.

While there are fancy polarity checkers that you can buy from companies like Van den Hul, the same tests can be done using a simple inexpensive digital voltmeter. First, disconnect all of the cables except the power cord from the component that you want to check, as any connection to other gear can throw off the results by providing multiple grounds. Then plug in the component using the normal orientation, but with the cheater plug in place. If the component uses a grounded cord, make sure to connect the green ground wire on the cheater plug to the outlet plate screw. Turn the component on, and set the voltmeter to A/C volts. I usually simply pinch one probe between the fingers of my left hand, then I hold the other probe in my right hand and touch the tip to a metal part of the component's casework such as a cover screw. Note the reading in volts. Turn off the component, reverse the plug in the wall outlet, turn the component on again and check the voltage once more at the same point on the case. If you got a lower reading this way, leave the component plugged in as it is, otherwise remove the cheater and plug it in normally.

If you repeat this test for each component, you should hear cleaner, more transparent high frequencies, and a lower overall noise floor. Total outlay? About five bucks. OK, $25 if you need to buy the multimeter, but still a bargain."

Yash

A propper designed PSU should not show any difference when AC is rectified to DC current. If you find there are difference either your PSU are faulty, the circuit use AC or there are noice comming through your AC inlet.

Have you tried it?

Either listened to it or measured it as Chip did before and after flipping the polarity?

If you think that's a "fault", it's in all PSUs since this is related to how transformers are built.