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possible to use powered speaker with hot signal?


Jeff_D_in_MD

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Is it possible to use an amplified signal (like that coming from a power amp to drive an unpowered speaker) with a powered speaker? I assume the inputs of the powered speaker want a line-level or mic-level signal and would get fried by the hotter signal, but perhaps I'm wrong. Is there a way to reduce the strength of the hot signal before sending it to the powered speaker?

 

The specific application I'm thinking is using the second channel on my QSC K10 to receive the vocal monitor feed from the PA. I currently use the QSC as my personal monitor for keys, and the other guys have unpowered wedge monitors for vocals. I would like to hear the vocalists better over the guitars.

Yamaha P2 acoustic, Yamaha P120 digital, Nord Electro 3HP, QSC K10.

FOR SALE: Nord Electro 2-61.

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Can you take a separate output from the board, an unused aux send? That's how I do it. Aux 1 goes to the singers monitor, aux 2 to me, aux 3 to the drummers in ears. I run my aux send into a separate EQ in my rack and then into my mixer, but you could run it into the 2nd input of the QSC as well. If you don't have a free aux send, then I'd get a Y adapter and tap into that. Running a speaker level signal is probably not a good thing.

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I agree with the above. However, this would do the job:

 

Rolls DB25b

 

That assumes that the K10 has balanced inputs which I believe is the case. It has an XLR connector, so you might need a balanced XLR-to-1/4 TRS cable.

 

This also assumes that the monitor send is either daisy-chained from another monitor, OR the venue's power amp is not tube-drive (which is a pretty safe bet these days). This box, combined with the line input on the K10, will present a high impedance to the power amp, which is fine for transistor amps (nearly equivalent to not plugging in a speaker) but is bad for most tube amps.

 

Rolls says it's even OK to use this with a mic input, though that bothers me.

 

When playing at a venue (someone else's PA), I'd ask for vocal monitors in this order:

 

1) separate speaker (why not, if there's room on stage?)

2) line monitor send

3) speaker monitor send, to use with the Rolls.

 

If it's your own PA for practice, just rig up a line level send. You can send one line level output to two line level inputs with a Y adaptor.

 

Finally, I'd call Rolls and ask them what the input impedance on this box is. If they say it passes the input impedance on from whatever the XLR is plugged into, then I would NOT use it to plug a speaker out into a low-Z mic input, despite their liturature. I expect that's the case; otherwise it would be more specific to the speaker-to-mixer application and would need a heafty heat sink.

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Is it possible to use an amplified signal (like that coming from a power amp to drive an unpowered speaker) with a powered speaker? I assume the inputs of the powered speaker want a line-level or mic-level signal and would get fried by the hotter signal, but perhaps I'm wrong. Is there a way to reduce the strength of the hot signal before sending it to the powered speaker? ....

 

My 17 year old did that to my rig as a toddler when I wasn't looking. My rig was a 6 channel box mixer and 2 - 15" 3-way cabnets. He unplugged a speaker and plugged the cable into the Power Amp In jack on a box mixer. Later I flipped the power on and it set the head on fire.

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You could run the hot signal through any direct box with an attenuation switch and knock it down 12dB (depending on the direct box) before sending to powered speaker. The tech at our last gig did this and it worked fine, although he still got some minor distortion when the band played louder (after the sound check was over and we started for real!) Obviously, turn the power amp down as much as possible ;) An aux output from the mixer is still the prefered method, however.

 

DRD

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You could run the hot signal through any direct box with an attenuation switch and knock it down 12dB (depending on the direct box) before sending to powered speaker. The tech at our last gig did this and it worked fine, although he still got some minor distortion when the band played louder (after the sound check was over and we started for real!)
What's the impedance on that, and how would it load the amp compared to an 8 ohm speaker?
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Well, the attennution circuit in your typical passive DI box consists of two switchable resistors on the input which are typically much higher than 8 ohms. The 'padded' resistor is on the order of 10K ohms, so I'm betting it will draw significantly less current than an 8 ohm speaker. DRD
Right, though I suspect the brunt of the impedance comes from the transformer.
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Well, the switch makes a significant change in the output level, so the resistors must be significant compared to the transformer, or it wouldn't make much difference. Unfortunately, calculating transformer input impedence with a mixed frequency input gets pretty hairy - beyond my limited abilities, I'm afraid!

 

DRD

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No, it's a great idea! Fire, man, fire!

 

Seriously, I suspect they'd connected the amp's output to its input. Connecting a speaker output to a line input is a bad, bad idea, but even for a 100W amp cranked all the way, typical parts could last hours before overheating and blowing -- and after that, it's just a dead input. At least, that's the theory, and YMMV.

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