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Post subject: Fender Rumble Amp: Phantom Power? Yes or no?
Posted: Sat Nov 22, 2014 6:04 am
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I have a Fender Rumble amp. The amp is equipped with one XLR Output Jack (Line Out) that sends a balanced signal to the mixer. My question is, if I engage (turn on) 48V Phantom Power on the mixer (my board has global Phantom Power, so I either send Phantom to all channels, or none), could the Phantom Power damage the amp? Is there documentation available that says that Phantom Power will, or will not damage the Amp? Thanks! Stereo Dogs (http://www.stereodogs.com)


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Post subject: Re: Fender Rumble Amp: Phantom Power? Yes or no?
Posted: Sat Nov 22, 2014 7:11 am
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No! Don't Do It!

Yes phantom power will damage your Rumble. Mic it instead.

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Post subject: Re: Fender Rumble Amp: Phantom Power? Yes or no?
Posted: Sat Nov 22, 2014 7:45 am
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Thanks for the prompt reply! :!: Appreciated!


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Post subject: Re: Fender Rumble Amp: Phantom Power? Yes or no?
Posted: Sat Nov 22, 2014 10:17 am
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I am NOT saying Linnen is wrong, but I am saying that you need to send this question via email to consumerrelations@fender.com along with your amp model name and serial. Like modern dynamic microphones, most XLR microphone level direct outputs on bass amplifiers will have a resistor in the direct out circuit to protect the amp from any voltage coming from phantom powered mixers. While 48 volts sounds like a lot of volts, it is very low current and easily buffered by a resistor in the circuit. HOWEVER even if they reply it is okay to do so I would NOT risk my amp by relying on a 4 cent resistor. Fender's schematics are only provided to service techs, so I can't look at the schematic to tell if it is protected and in reading several PDF manuals for various Rumbles it doesn't say anything about whether or not it is protected.

Instead of using a microphone I'd strongly encourage using an active direct injection box between the amp and the phantom power. This will do a couple of things, the most important of which is totally protect your amp. It also preserves fidelity and signal strength on longer cable runs since it is active. These boxes are designed to use the phantom power on their output side to power the box's operation without passing any current at all to the audio source on the input side of the box. Zero volts.

The Behringer Ultra-DI DI100 Active Direct Box is $40 and perfectly adequate. There are more expensive active direct boxes available from other lines like Countryman, Whirlwind and Radial Engineering. Most passive direct injection boxes and even some active direct injection boxes (like the Radial Engineering J48 which is a very good box) do not have an XLR input jack and they only have an XLR output jack with phone plug input jacks. That would not work in this situation. You'll need one with an XLR on both the input and the output and the Behringer DI100 has them.

Or as Linnen said you can mic the cab, but the box is cheaper and will probably sound better. Either solution will work, but probably the active direct injection box is the best solution. Like I said even if Fender replies that it is perfectly safe to use it with phantom power engaged, I'd still feel more comfortable with an active direct injection box in between any XLR amp direct output and phantom power.

Another solution is to get a mixer with phantom power that is selectable on/off for each input channel. That is probably the most expensive solution and yet it is not as foolproof as the active direct injection box since switches can be bumped.


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