Phantom power affecting keyboard volume?!

beatdat

Senior Member
So, an interesting issue came up the other day in the church group I play with.

I got to church on Sunday morning to rehearse before the service. The rest of the band was already there and practicing, but the keyboard volume was unbearable loud. I looked at the fader volume, the gain, and the rest of the mixer for anything out of the ordinary, but didn't notice anything. Not knowing what to do, I turned the keyboard's fader volume down nearly as far as it could go. We play our first song, and the keyboard is still too loud.

After the first song, I returned to the mixing board and, while the pastor is giving his sermon, I noticed that the phantom power button was turned off. Since I need the phantom power for my cymbal microphones, I turned it back on. When it comes time to start our next song, the keyboard now has little volume to it. Fortunately, the cameraman noticed this and, while we were playing, slides the keyboard fader back to its regular position. Problem solved.

Yesterday, I tried to do a little research on this, but couldn't come up with much. The only thing I found was that phantom power can sometimes damage an instrument (particularly a keyboard) if an unbalanced TRS line connects the instrument to the mixer. In our instance, though, we connect the keyboard to the mixer via XLR. Other suggestions were to use a DI box in between the instrument and the mixer, but we were advised to go direct using XLR cables since our keyboard apparently has a powerful DI built into it.

My questions are two-fold:

1) Why would turning the phantom power off result in a drastically increased keyboard volume when the keyboard doesn't rely on phantom power?; and

2) Is there any chance of damaging the keyboard while using phantom power for the cymbal microphones?

For reference, the mixer is a Soundcraft Signature 22 MTK, and the keyboard is a Roland RD-2000.

Any thoughts?

Thanks.
 

beatdat

Senior Member
Have you tried the actual DI box approach yet?
Not yet, but it would be easy to do since we have an extra input in the DI box we use for the bass guitar. Will give it a shot at rehearsal tonight if we have time.

But, what should I be looking/listening for? To see/hear if there's a difference in volume when phantom power is turned on or off while the keyboard is connected to the DI?
 

Bo Eder

Platinum Member
Not yet, but it would be easy to do since we have an extra input in the DI box we use for the bass guitar. Will give it a shot at rehearsal tonight if we have time.

But, what should I be looking/listening for? To see/hear if there's a difference in volume when phantom power is turned on or off while the keyboard is connected to the DI?
I’m suspecting if you were using a regular 1/4-to-XLR (male) cable initially, phantom power could be affecting that cable since that 48 volts is applied to one of the XLR pins - so I would suspect a bad cable. But if you do it the traditional way, 1/4” mono cable to DI, then XLR to the console, that should alleviate the issue. Unless your console has dedicated “Hi Z” inputs, I suspect the phantom power did affect your signal from the keyboard?
 

beatdat

Senior Member
I’m suspecting if you were using a regular 1/4-to-XLR (male) cable initially, phantom power could be affecting that cable since that 48 volts is applied to one of the XLR pins - so I would suspect a bad cable. But if you do it the traditional way, 1/4” mono cable to DI, then XLR to the console, that should alleviate the issue. Unless your console has dedicated “Hi Z” inputs, I suspect the phantom power did affect your signal from the keyboard?
I always appreciate your help, so I’ll keep looking into that.

I’m fairly certain that the mixer has some “Hi Z” inputs, but I have no idea what they’re for.

Putting together this A/V setup for the church has been quite an experience, and, honestly, I couldn’t have done it without the help of a good friend of mine and a bunch of y’all, as well.
 

Bo Eder

Platinum Member
I always appreciate your help, so I’ll keep looking into that.

I’m fairly certain that the mixer has some “Hi Z” inputs, but I have no idea what they’re for.

Putting together this A/V setup for the church has been quite an experience, and, honestly, I couldn’t have done it without the help of a good friend of mine and a bunch of y’all, as well.
“Hi Z” inputs would be the 1/4-inch input which is supposed to allow you to plug a guitar in directly. They could also be labeled as “Line” inputs because anything line level would be high impedence. But I think it’s always best to just use a DI box for connections like that, because the box is converting high impedence to low impedence on its way to the console, increasing the length of your cable run from instrument to console.
 

Morrisman

Platinum Member
I presume your keyboard has XLR outputs as well as the usual jacks, and that’s what you’re using to connect to the PA system. Properly wired XLR outputs should ignore phantom power.
Unless there’s a fault in the keyboard, the sudden change must be due to something else.
Did anyone touch the ‘Pad’ button on the mixer and didn’t realise? Or a mic/line switch at the back of the keyboard?
Only way to check is to plug the keyboard in again and try and replicate the issue.
Edit: if the keyboard is at fault, do what Bo suggested - run a jack output into a DI box, then XLR cable to the mixer. Then the phantom power won’t reach the keyboard.
 
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