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Author Topic: JBL VRX900 series amplifier config  (Read 6373 times)

Josh West

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JBL VRX900 series amplifier config
« on: May 29, 2015, 11:47:12 pm »

Power question, because I'm getting different stories from different distributors/salesmen.
I'm looking at running a series of 3 VRX935LA-1's per array, with a single VRX918S sub on each side.  For the sake of redundancy and cost I was considering running each box off of a single Crown XTI 1002 in bridged mono mode.
Quick specs so you don't have to look them up:
VRX935LA-1 Continuous/Program/Peak wattage 800/1600/3200
VRX918s      Continuous/Program/Peak wattage 800/1600/3200, nominal impedance 8ohm (same as the speakers)
Crown XTi 1002 amplifier 1000w mono bridged mode at 8ohm.

I realise there are better configurations using more powerful amps (my next consideration being the ITech 5000) however the price point of those amps and the impact of losing a single channel prompts me to use smaller amps.

Do you see any blatant problems with running the small amp configuration?  Are there any known issues in running XTI's in mono bridge mode?
Any advice is welcome :) thanks for reading

Josh
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Tim Weaver

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Re: JBL VRX900 series amplifier config
« Reply #1 on: May 30, 2015, 12:50:42 am »

There's nothing inherently wrong with it, but I don't like using bridged amps generally. Why can't you use an XTI4000 or 6000 in stereo? First amp ch1-top vrx, ch2 middle vrx. Amp 2 is lower vrx and the sub.

Repeat for the other side. That gives you plenty of redundancy and the amps will like you better
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Josh West

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Re: JBL VRX900 series amplifier config
« Reply #2 on: May 30, 2015, 03:07:07 am »

There's nothing inherently wrong with it, but I don't like using bridged amps generally. Why can't you use an XTI4000 or 6000 in stereo? First amp ch1-top vrx, ch2 middle vrx. Amp 2 is lower vrx and the sub.

Repeat for the other side. That gives you plenty of redundancy and the amps will like you better

Thanks for the reply Tim.  The 4002's strike me as being underpowered, especially for the subwoofers, producing 650w at 8 ohm in stereo.   I had considered running 3 4002's with 1 6002 for the subs, it does come to being slightly more expensive.  The prices (in Australia) are nearly identical for 2 1002's or 1 4002, however the 1002 will be pushing an extra 350 watts per box.

Regarding the hardware, is there a particular reason the amps would prefer operating in stereo rather than mono bridge?  Power supply is the only thing that comes to my mind, or perhaps capability of capacitors which are shared by both channels.

Cheers again for the input.
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Tim Weaver

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Re: JBL VRX900 series amplifier config
« Reply #3 on: May 30, 2015, 02:12:59 pm »

Under powered for what? Is this for spoken word? A 250 watt amp would probably work.

Doing metal shows? You need a bigger amp
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Josh West

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Re: JBL VRX900 series amplifier config
« Reply #4 on: May 30, 2015, 06:18:16 pm »

Under powered for what?

Fair question.  It's a multi purpose church hall which gets used for a range of things, including some fairly rowdy distorted and heavy bass music.
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Scott Carneval

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Re: JBL VRX900 series amplifier config
« Reply #5 on: June 03, 2015, 09:20:40 am »

Power question, because I'm getting different stories from different distributors/salesmen.
I'm looking at running a series of 3 VRX935LA-1's per array, with a single VRX918S sub on each side.  For the sake of redundancy and cost I was considering running each box off of a single Crown XTI 1002 in bridged mono mode.
Quick specs so you don't have to look them up:
VRX935LA-1 Continuous/Program/Peak wattage 800/1600/3200
VRX918s      Continuous/Program/Peak wattage 800/1600/3200, nominal impedance 8ohm (same as the speakers)
Crown XTi 1002 amplifier 1000w mono bridged mode at 8ohm.

I realise there are better configurations using more powerful amps (my next consideration being the ITech 5000) however the price point of those amps and the impact of losing a single channel prompts me to use smaller amps.

Do you see any blatant problems with running the small amp configuration?  Are there any known issues in running XTI's in mono bridge mode?
Any advice is welcome :) thanks for reading

Josh

It will work, there's no question about that, but I'm not a fan of bridged amps if you can avoid it.  I would also suggest 4002's or 6002's in stereo if you can afford it.  Also, I assume you're talking about the VRX932?  There is no VRX935 that I'm aware of.

Do you already own the system?  The new SRX powered series is really nice, and you won't have to worry about amps or processing.
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TJ (Tom) Cornish

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Re: JBL VRX900 series amplifier config
« Reply #6 on: June 03, 2015, 10:22:23 am »

Fair question.  It's a multi purpose church hall which gets used for a range of things, including some fairly rowdy distorted and heavy bass music.
+1 on the new SRX series instead of VRX.  6 boxes of VRX plus 2 VRX subs plus amps and DSP to run them is $$$$.  You'd be ahead in output and sound quality to either get into more modern powered boxes, or to look at a high quality horn-loaded box that would fit the room (Danley, EAW qxi).  In either case, your cost will be lower, and sound quality will be higher.

As to bridged vs stereo, bridging the amp effectively runs the amp in 2Ω per channel mode, which creates more strain on the amp due to having to provide a lot more current.  One larger amp run in 4Ω stereo mode would be significantly better than two smaller amps bridged. 

Also back to your VRX plan (which wouldn't be my first or second choice in your scenario), it's unclear to me what you mean by "running each box off a single Crown XTI 1002 bridged".  If you are intending to use 6 XTI 1002s - one for literally each VRX932, you are wasting your time.  Get a new or used ITechHD 9000 and run 3 boxes per side using the V5 preset and the attenuator switches in the VRX to notch the bottom box down 3dB if you want.  Performance, sound quality, power consumption, and rack space will be much better with a single real amp rather than a rack of relatively low-grade amps that are too small.
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Tim McCulloch

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Re: JBL VRX900 series amplifier config
« Reply #7 on: June 27, 2015, 02:05:53 pm »

+1 on the new SRX series instead of VRX.  6 boxes of VRX plus 2 VRX subs plus amps and DSP to run them is $$$$.  You'd be ahead in output and sound quality to either get into more modern powered boxes, or to look at a high quality horn-loaded box that would fit the room (Danley, EAW qxi).  In either case, your cost will be lower, and sound quality will be higher.

As to bridged vs stereo, bridging the amp effectively runs the amp in 2Ω per channel mode, which creates more strain on the amp due to having to provide a lot more current.  One larger amp run in 4Ω stereo mode would be significantly better than two smaller amps bridged. 

Also back to your VRX plan (which wouldn't be my first or second choice in your scenario), it's unclear to me what you mean by "running each box off a single Crown XTI 1002 bridged".  If you are intending to use 6 XTI 1002s - one for literally each VRX932, you are wasting your time.  Get a new or used ITechHD 9000 and run 3 boxes per side using the V5 preset and the attenuator switches in the VRX to notch the bottom box down 3dB if you want.  Performance, sound quality, power consumption, and rack space will be much better with a single real amp rather than a rack of relatively low-grade amps that are too small.

This is 100% good advice, in my experience.

The only reason to use a separate amp for each VRX box (and they need to be bi-amped to do it well) is to do some custom array shading for pattern control.  One of the guys at Meeting Systems (San Diego) talked about this several years ago and I recall it wasn't easy, but was the result of making the VRX perform better in situations where the form factor and weight were important.  At that time there were fewer small, light loudspeakers that offered similar performance, now there are many more options.

Josh, if you can't make a pretty picture with JBL's VRX LAC, this is the wrong box for the project (which I think it may be, anyway).  Rhetorical question:  Why is a church in the business of supplying sound systems for rowdy, bass-heavy music (presumably not part of church service) and (non-rhetorically) what does the top box have to do with "bass heavy"?
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Jamin Lynch

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Re: JBL VRX900 series amplifier config
« Reply #8 on: June 28, 2015, 12:34:49 pm »

Power question, because I'm getting different stories from different distributors/salesmen.
I'm looking at running a series of 3 VRX935LA-1's per array, with a single VRX918S sub on each side.  For the sake of redundancy and cost I was considering running each box off of a single Crown XTI 1002 in bridged mono mode.
Quick specs so you don't have to look them up:
VRX935LA-1 Continuous/Program/Peak wattage 800/1600/3200
VRX918s      Continuous/Program/Peak wattage 800/1600/3200, nominal impedance 8ohm (same as the speakers)
Crown XTi 1002 amplifier 1000w mono bridged mode at 8ohm.

I realise there are better configurations using more powerful amps (my next consideration being the ITech 5000) however the price point of those amps and the impact of losing a single channel prompts me to use smaller amps.

Do you see any blatant problems with running the small amp configuration?  Are there any known issues in running XTI's in mono bridge mode?
Any advice is welcome :) thanks for reading

Josh

Good reading.

http://www.jblpro.com/ProductAttachments/VRX.AppGuide.pdf

Or get self powered VRX's and take out all the guess work
« Last Edit: June 28, 2015, 12:42:32 pm by Jamin Lynch »
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Keith Broughton

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Re: JBL VRX900 series amplifier config
« Reply #9 on: June 28, 2015, 03:32:05 pm »

Quote
bridging the amp effectively runs the amp in 2Ω per channel mode,
Is that correct?
A load of 8 ohms on a bridged amp should have the amp "seeing" 4 ohms / ch not 2.
Also, what's wrong with running amps bridged if they are designed to do so?
 Seems like his 1 amp/ box should be just fine.
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Re: JBL VRX900 series amplifier config
« Reply #9 on: June 28, 2015, 03:32:05 pm »


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