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XLR vs Jack

 
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cenica



Joined: 21 Apr 2017
Posts: 8

PostPosted: Wed Apr 26, 2017 11:10 am    Post subject: XLR vs Jack Reply with quote

Unless I cut -20 db, a (bearable, but still...) hum comes from the jack outputs. On the contrary, XLR outputs give me a really clean and loud signal, so I think I will use them hereafter... But, since on my other keyboards I've always been using jacks and DI, I was wandering: is there any precaution needed when plugging XLR cables?
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voip
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Joined: 27 Nov 2014
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PostPosted: Wed Apr 26, 2017 1:11 pm    Post subject: Reply with quote

If there is significant hum on the audio coming from the SV-1's jack outputs, it would be worth examining the grounding arrangements of the amplifier and keyboard. Since the SV-1's jack outputs are unbalanced, they will always be more prone to hum, picked up from nearby mains wiring, transformer stray fields, motors, and the like, finding its way to the loudspeakers. Ideally, the amp mains lead and SV-1 power lead should come off the same outlet and the ground connections should be solid, and the mains cables for amp and keyboard should run close to each other. The audio leads should not be bundled with, or run close to the mains cables, nor should they be a long distance apart. Also, the audio lead should be made using good quality screened cable. Unscreened cable should not be used. The screens should have good connections to the jack plug sleeves at each end, and the jack plug and socket contacts should be clean, and not oxidised.

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cenica



Joined: 21 Apr 2017
Posts: 8

PostPosted: Wed Apr 26, 2017 3:03 pm    Post subject: Reply with quote

Thank you. I'm aware of all this details, but it seems more difficult to get an ideal situation for the sv1 than for other keyboards: I also play a Prophet with unbalanced jacks, tried the same plugging used with the sv1, and there was no hum at all.
So: what about these very clean XLR outputs which I'm not used to, but already like a lot? Do I have to pay attention to something if I use them, or can I just plug and play?
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voip
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PostPosted: Wed Apr 26, 2017 7:12 pm    Post subject: Reply with quote

The XLR cables will pick up just as much hum as the single-ended jack cables, but the hum will be induced in both signal leads more or less equally and therefore pass to the amplifier as a common-mode signal that gets cancelled out by the amplifier inputs. That's why it sounds relatively clean in your case. Bear in mind that large amounts of hum induced into a balanced cable could overload the amplifier input, depending on its circuit configuration, and result in distortion.

It is worth considering the possibility that the SV-1 may have a real grounding issue on the single-ended jack outputs, as excessive hum really shouldn't be present.

It should be OK to plug and play. Some folks use a DI box between XLRs and amp, to get some extra isolation. Worth considering if playing at venues where the house PA could be a bit "dodgy".

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PianoManChuck
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Joined: 09 Aug 2011
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Location: Los Angeles, CA

PostPosted: Wed Apr 26, 2017 9:48 pm    Post subject: Re: XLR vs Jack Reply with quote

cenica wrote:
Unless I cut -20 db, a (bearable, but still...) hum comes from the jack outputs. On the contrary, XLR outputs give me a really clean and loud signal, so I think I will use them hereafter... But, since on my other keyboards I've always been using jacks and DI, I was wandering: is there any precaution needed when plugging XLR cables?

If you're using XLR cables and plugging in to a mixer or audio interface (or anything else), make absolutely certain that any Phantom Power switch(es) on that input device are OFF!!!!
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cenica



Joined: 21 Apr 2017
Posts: 8

PostPosted: Thu Apr 27, 2017 10:36 am    Post subject: Reply with quote

Thanks very much to both of you.
As I said, the hum is bearable (let's say a bit less than a guitar amp; obviously I switched off my amp simulator, which however is almost inaudible, unless I pick up my volume to top), but definitively louder than that from another keyboard in the same situation (which however is not strictly ideal...).
@PianoManChuck, your answer sounds kind of scary: what would be the consequences of a Phantom Power on? Is there any protection against that? Something like SV1 > xlr female - jack cables > DI > xlr cables > mixer/PA could be of any use? If so, do the xlr female - jack cables have to be mono or stereo?
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PianoManChuck
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PostPosted: Thu Apr 27, 2017 5:49 pm    Post subject: Reply with quote

cenica wrote:

@PianoManChuck, your answer sounds kind of scary: what would be the consequences of a Phantom Power on?

Condenser microphones are VERY popular in recording studios, but they require an external power source in order to work. They're so popular that many mixing boards and audio interfaces provide that power source - its called Phantom Power and if your board has it, it can be turned on or off with a switch on the board that should be clearly labeled "Phantom Power". Not all channels of all boards offer it, some offer it on the first 2 XLR inputs, others on all XLR inputs (there will be a separate switch for each channel that offers it), and some boards don't offer it at all. (When I say "boards" it can actually be a mixing console, and audio interface, an audio recorder, or even an amp / PA).

Normally the pins on an XLR cable point to the direction of signal flow (microphones have the 3 pins on them that point in the direction of signal flow from the microphone to whatever its connected to - usually an XLR cable where the female end connects to the microphone body, and the male end goes to your device / board). The pins on the male end indicate that the signal is flowing out of that end, whereas the female XLR input on your device means the signal flows into that device.

The exception to this signal flow is with Phantom Power. Phantom power (12 to 48 volts) flows the opposite direction so that it can supply condenser mics with the voltage it needs to operate. So of the 3 pins, 2 conduct flow from the mic to the device, whereas another 2 supply voltage TO the mic (one of the pins is a ground in each case).

So the bottom line in a nutshell is, if you have phantom power ON, you're sending voltage back to your keyboard which can cause damage.
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cenica



Joined: 21 Apr 2017
Posts: 8

PostPosted: Thu Apr 27, 2017 7:16 pm    Post subject: Reply with quote

Ok, that IS scary: thank you so much for warning me!
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