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Author Topic: Amps in Parallel  (Read 3724 times)

Nick Holmquist

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Amps in Parallel
« on: August 09, 2015, 12:25:29 am »

A bit confused about an audio system that is about to be installed at our university, and I'm hoping you can help me out.

Here is what we have:

6 x JBL928LAs, 3 per side
3 x Crown XTi 4002s
2 x 150' Pro Co NL4
4 x 1.5' Pro Co NL4
1 x Driverack

How to hook this up? I think the plan was to run the two long runs of NL4 to the speakers in parallel (wired with the short NL4 jumpers), which would drop the impedance to 2.7 ohms (JBL is saying 3).

The amps will do 1400W at 3 ohms in stereo mode (min guaranteed by Crown), but JBL recommends at least 3000W at 3 ohms per side for all three speakers.

The amps support 4 and 8 ohm bridging only. It puts out 3200W at 4 ohms bridged, so it's tempting, but I don't think it's safe to run 3 ohms if it's not listed.

I have heard about doing parallel or bridged parallel amplifier setups, but I'm not clear on that. I understand how to send signal from one amp to another, but does running in parallel also send power, like you can add up the power from multiple amps? Seems like it could blow stuff up...

Sorry if it's a stupid question (seems like it wouldn't work), but I read was something like, multiple amps share the one load, which sounds like what I'm trying to do. A few other posts online seem to confirm, but I need to be sure!

So running the amps in parallel sounds like what I want to do, similar to running the speakers in parallel, but don't know if or how it works!


If that doesn't work, other possibilities:

1) Buy two more pairs of long NL4, one for each amp and set of speakers. Then I can use all three outputs of the Driverack.

2) Buy one more run of long NL4. One amp runs its own pair of speakers over its own run of NL4. The other two amps run bridged, with two speakers in parallel per side/amp. Would save money on that long expensive cable

3) Try to exchange the amps for one more powerful amp, maybe DCi 4-1250 (would be tough to swing that)

4) Pray that running one 4002 amp bridged to each side is enough, and use the third amp elsewhere

5)  Some creative way of wiring up the NL4? Could I "Y" two outputs into channel 1 and combine with channel 2 to run through the one pair of long NL4s or something?


If you have read this far, thanks! Really appreciate any constructive feedback!!!



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Scott Holtzman

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Re: Amps in Parallel
« Reply #1 on: August 09, 2015, 12:52:18 am »

A bit confused about an audio system that is about to be installed at our university, and I'm hoping you can help me out.

Here is what we have:

6 x JBL928LAs, 3 per side
3 x Crown XTi 4002s
2 x 150' Pro Co NL4
4 x 1.5' Pro Co NL4
1 x Driverack

How to hook this up? I think the plan was to run the two long runs of NL4 to the speakers in parallel (wired with the short NL4 jumpers), which would drop the impedance to 2.7 ohms (JBL is saying 3).

The amps will do 1400W at 3 ohms in stereo mode (min guaranteed by Crown), but JBL recommends at least 3000W at 3 ohms per side for all three speakers.

The amps support 4 and 8 ohm bridging only. It puts out 3200W at 4 ohms bridged, so it's tempting, but I don't think it's safe to run 3 ohms if it's not listed.

I have heard about doing parallel or bridged parallel amplifier setups, but I'm not clear on that. I understand how to send signal from one amp to another, but does running in parallel also send power, like you can add up the power from multiple amps? Seems like it could blow stuff up...

Sorry if it's a stupid question (seems like it wouldn't work), but I read was something like, multiple amps share the one load, which sounds like what I'm trying to do. A few other posts online seem to confirm, but I need to be sure!

So running the amps in parallel sounds like what I want to do, similar to running the speakers in parallel, but don't know if or how it works!


If that doesn't work, other possibilities:

1) Buy two more pairs of long NL4, one for each amp and set of speakers. Then I can use all three outputs of the Driverack.

2) Buy one more run of long NL4. One amp runs its own pair of speakers over its own run of NL4. The other two amps run bridged, with two speakers in parallel per side/amp. Would save money on that long expensive cable

3) Try to exchange the amps for one more powerful amp, maybe DCi 4-1250 (would be tough to swing that)

4) Pray that running one 4002 amp bridged to each side is enough, and use the third amp elsewhere

5)  Some creative way of wiring up the NL4? Could I "Y" two outputs into channel 1 and combine with channel 2 to run through the one pair of long NL4s or something?


If you have read this far, thanks! Really appreciate any constructive feedback!!!

Please change to your real name per forum rules to have your questions answered.  This requirement is on top of every page in the forum:

"Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums"
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Scott AKA "Skyking" Holtzman

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Ray Aberle

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Re: Amps in Parallel
« Reply #2 on: August 10, 2015, 09:59:45 pm »

Who spec'd this system? Who sold it to you?

Why are they not the ones who are setting it up for you?

If you spec'd the system and encouraged its purchase, why did you choose the products that you did? If it was at the suggestion of a salesperson at, say, Banjo Hut, you need to go back and insist that they better prepare you for your new rig. i.e. if that is the gear they suggested based on the needs that you surely explained to them, then they need to be able to defend that decision.

Why are you getting a DriveRack when the XTis that you are purchasing have sufficient DSP available, especially given that you get presets from Crown and JBL to support these speakers?

Just some quick thoughts before my pizza comes out of the oven...
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Paul G. OBrien

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Re: Amps in Parallel
« Reply #3 on: August 11, 2015, 03:16:01 pm »

A bit confused about an audio system that is about to be installed at our university, and I'm hoping you can help me out.

Here is what we have:

6 x JBL928LAs, 3 per side
3 x Crown XTi 4002s
2 x 150' Pro Co NL4
4 x 1.5' Pro Co NL4
1 x Driverack

How to hook this up?

Very strange. With the supplied cables the most that can be achieved is a biamped config with 2 of the amps running dual channel mode, so what is the 3rd amp for and the Driverack is totally redundant.

As for the question in the title of this thread, you cannot simply connect the output of 2 or more amplifier channels to a single speaker load, that just shorts one amp to another which is a great way to blow them up. Do not confuse this with the parallel or dual mono mode some amps have where both channels are fed from a single input signal but are still connected to their own separate speaker loads, or with bridged mono mode where two channels in a common chassis are bridged together to form a single more powerful amp channel. In this case the input signal to one of those channels is reversed polarity so that the outputs sum correctly.

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g'bye, Dick Rees

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Re: Amps in Parallel
« Reply #4 on: August 11, 2015, 03:38:11 pm »

From a practical point of view, none of what you've posted makes much sense.
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Scott Holtzman

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Re: Amps in Parallel
« Reply #5 on: August 11, 2015, 06:29:06 pm »

Very strange. With the supplied cables the most that can be achieved is a biamped config with 2 of the amps running dual channel mode, so what is the 3rd amp for and the Driverack is totally redundant.

As for the question in the title of this thread, you cannot simply connect the output of 2 or more amplifier channels to a single speaker load, that just shorts one amp to another which is a great way to blow them up. Do not confuse this with the parallel or dual mono mode some amps have where both channels are fed from a single input signal but are still connected to their own separate speaker loads, or with bridged mono mode where two channels in a common chassis are bridged together to form a single more powerful amp channel. In this case the input signal to one of those channels is reversed polarity so that the outputs sum correctly.

The OP is MIA, they corrected their name but have not updated the thread.  Too bad, interesting mystery.
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Scott AKA "Skyking" Holtzman

Ghost Audio Visual Solutions, LLC
Cleveland OH
www.ghostav.rocks

g'bye, Dick Rees

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Re: Amps in Parallel
« Reply #6 on: August 11, 2015, 06:42:34 pm »

The OP is MIA, they corrected their name but have not updated the thread.  Too bad, interesting mystery.
l

Well, he logged in this afternoon so he's seen the responses up to and through Pauls.
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Brandon Scopel

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Re: Amps in Parallel
« Reply #7 on: August 11, 2015, 11:55:10 pm »

Maybe whoever bought it expects them to bridge two of the xti4002 for low end. One per side, then have one channel per side on the remaining amp for highs. He would need a patch panel for that or take the speakon off.

Sent from my D6708 using Tapatalk

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Re: Amps in Parallel
« Reply #7 on: August 11, 2015, 11:55:10 pm »


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