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Grounded keyboards/synthesizers/workstations


Theo Verelst

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Bit boring it sounds, but I just found out (measured) the (Yamaha, obviously) CP4 has ground separated outputs!

 

That means that both the balanced and the unbalanced audio outputs, which have the signal grounds connected together, are *NOT* connected to the earth, i.e. the ground pin of the mains connector and plug. That's very good to prevent grounding loops (hum), and not always the case, like I reported a while back the PC3 has it's audio grounds hard connected to the power ground pin.

 

T.V.

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Bit boring it sounds, but I just found out (measured) the (Yamaha, obviously) CP4 has ground separated outputs!

 

That means that both the balanced and the unbalanced audio outputs, which have the signal grounds connected together, are *NOT* connected to the earth, i.e. the ground pin of the mains connector and plug. That's very good to prevent grounding loops (hum), and not always the case, like I reported a while back the PC3 has it's audio grounds hard connected to the power ground pin.

 

T.V.

If only it was as straightforward as that. However, whether or not to isolate audio cable shields from chassis ground (which is often also power ground) can be complicated, and there's no guarantee that either way will result in hum-free operation.

 

For a more in-depth perspective, see http://www.rane.com/note151.html

 

Yamaha: Motif XF6 and XS6, A3000V2, A4000, YS200 | Korg: T3EX, 05R/W | Fender Chroma Polaris | Roland U-220 | Etc.

 

 

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It *IS* straightforward what I wrote, I state I measured there's a very high impedance between the ground of the supply wires and the outputs. That's beneficial in every case except the degenerate case of expecting an amount of ground current to run through the audio "cold" connection.

 

The outputs are separate from the internal metal chassis which is safety grounded by the supply plug. That's a plus no matter what you do with balanced or unbalanced wires, because there will be no grounding loop introduced by the CP4 in any case.

 

T.

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It *IS* straightforward what I wrote, I state I measured there's a very high impedance between the ground of the supply wires and the outputs. That's beneficial in every case except the degenerate case of expecting an amount of ground current to run through the audio "cold" connection.

 

The outputs are separate from the internal metal chassis which is safety grounded by the supply plug. That's a plus no matter what you do with balanced or unbalanced wires, because there will be no grounding loop introduced by the CP4 in any case.

 

T.

My point was that ground isolation doesn't ensure the best performance when it comes to hum reduction. Ground potential differences aren't the only manner in which hum can be induced.

Yamaha: Motif XF6 and XS6, A3000V2, A4000, YS200 | Korg: T3EX, 05R/W | Fender Chroma Polaris | Roland U-220 | Etc.

 

 

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Hummer on the ground

Dan

 

Acoustic/Electric stringed instruments ranging from 4 to 230 strings, hammered, picked, fingered, slapped, and plucked. Analog and Digital Electronic instruments, reeds, and throat/mouth.

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My Vortex was behaving inappropriately, so I grounded it for a month. No more gigs until May 1.

 

Oh, wait.. Never mind

 

:poke:

:facepalm:

:rimshot:

 

HAHAHA! That won't work with a couple of mine.. They are well beyond the drinking age.. I know, I know - I should just give them the: "I don't care how old you are, you're still living under my roof!" I just don't want to sound like my old man.

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Waiting for musical instrument standard opto-isolated digital audio IO.....

MIDA (Musical Instrument Digital Audio)? :)

 

Or rather than a new standard, Toslink.

 

 

 

Yamaha: Motif XF6 and XS6, A3000V2, A4000, YS200 | Korg: T3EX, 05R/W | Fender Chroma Polaris | Roland U-220 | Etc.

 

 

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It's a lot of EE magic, ground and ground voltage and current, locally and globally over a neighborhood, interesting subject.

 

Some trade-offs for keyboards and small amps: USB is not ground lifted (it is possible to do, but seldom happens), so the USB creates a ground loop with the computer supply+grounding. Ground currents inducing disturbance can hardly be fought, except by balancing, which I've done but it's not the best way. Also, even shielded and balanced cables can still pick up magnetic and "transmitter" induced hum and rattle, that's a matter of wire electronics and the fact that the shield of a cable hardly stops magnetic fields at all (not even metal cases do that very well).

 

Using a standard transformer can make your electronics "floating" with respect to the ground, which is good, because: not ground loops, no ground currents, less disturbance sources. The problem with modern switched supplies is that they connect to the ground in a way which creates noise on the ground, and that's hard to get rid of. So we can joke about making some sort of deal to deal with all that, but even if you hide all kinds of strange disturbance signals by choosing your audio signals that go over the cables carefully, the more perfect solution will let you alleviate most of the problem by approximating perfection using cables with no loops, good symmetrical and very even shielding and inner wires, possibly ferrite beads against high frequency effects, potent signal ground boost circuits and difference amplifiers at the input of mixers/amps that have low noise, low distortion, high frequency accuracy, and very good Common Mode Rejection Ratio. Many of these electronics and physics demands are contradicting each others preferences, so it's a lot of work to make audio systems that work good in all circumstances.

 

From what I gather, the Yamaha uses a staged switched supply, and apparently not a "earth" ground coupled audio output, which I prefer. There are certain safety considerations in the play, like how much isolation voltage withstanding capacity does that require, and what are the worst voltages possibly building up anywhere in the audio systems with such a component in it. (Ever see the light dim when you switch on a heavy amp, or sparks in the socket when you plug in a switched supply? That needs to be safe)

 

T.

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