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Author Topic: QRX 212/75 Problem - Big Problem  (Read 12601 times)

Steve Alves

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Re: QRX 212/75 Problem - Big Problem
« Reply #20 on: April 03, 2012, 09:20:05 pm »

Yup, its just about right, 600W/driver continuous. There is ~2db reserve in the QSC so about 800W, thereabouts.

The limiting on the drive rack should handle the overpower but I am guessing when the power was cut to the amps, the thud was 2400 watts into the mids.
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Steven Alves
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Re: QRX 212/75 Problem - Big Problem
« Reply #21 on: April 03, 2012, 10:01:03 pm »

The limiting on the drive rack should handle the overpower but I am guessing when the power was cut to the amps, the thud was 2400 watts into the mids.

I won't claim that this is what happened, but it could be that when the power was cut it was the turn-off spike from the DriveRack hitting the amps while they still had enough of a charge to send the amplified spike to the speakers.  The DR limiting would have no effect at all if it was the unit itself sending the spike.

Another possible reason for having a UPS at FOH........idiot protection for those who'd pull the plug on you.
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Tomm Williams

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Re: QRX 212/75 Problem - Big Problem
« Reply #22 on: April 04, 2012, 03:22:16 pm »

I won't claim that this is what happened, but it could be that when the power was cut it was the turn-off spike from the DriveRack hitting the amps while they still had enough of a charge to send the amplified spike to the speakers.  The DR limiting would have no effect at all if it was the unit itself sending the spike.

Another possible reason for having a UPS at FOH........idiot protection for those who'd pull the plug on you.

Interesting theory, sounds quite plausible.
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Matt Vivlamore

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Re: QRX 212/75 Problem - Big Problem
« Reply #23 on: April 04, 2012, 05:10:51 pm »

The previous 3 posters all run QRX212s and we don't use that amount of power.


Sent from my iPhone using Tapatalk


Well I use an IT4000... but then again I have the RMS limiter is set at 600w @ 4 ohms.  Before that, I was using an XTi4000. 
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Steve Alves

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Re: QRX 212/75 Problem - Big Problem
« Reply #24 on: April 05, 2012, 10:09:14 pm »

While we are on this topic, how do (2) 212/75's per side over (1) 218 per side sound? Can the single 218's keep up?

I have a deal to get two more and can't make up my mind.

I was also told that it is more likely that something on the internal board probably went and not all 4 drivers. I am waiting for a callback from EV Tech.
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Steven Alves
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Mike Christy

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Re: QRX 212/75 Problem - Big Problem
« Reply #25 on: April 06, 2012, 05:58:34 am »

While we are on this topic, how do (2) 212/75's per side over (1) 218 per side sound? Can the single 218's keep up?

I have a deal to get two more and can't make up my mind.

I was also told that it is more likely that something on the internal board probably went and not all 4 drivers. I am waiting for a callback from EV Tech.


We've used 6 Growlers center clustered on a PL6 with 2 Qrx212/75s a side, it was just about right. You could conservatively equate a Growler to 1.5 x 18, so with coupling, we had 4 218s, roughly. Depends on the style and venue of course for your needs.

Mike
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John Penkala

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Re: QRX 212/75 Problem - Big Problem
« Reply #26 on: April 06, 2012, 07:08:47 am »

The limiting on the drive rack should handle the overpower but I am guessing when the power was cut to the amps, the thud was 2400 watts into the mids.

 Cutting power to the amps shouldn't result in blowing speakers. The output relays of the DR260 should open. However, applying phantom power to a wide-open mic could cause this or loosing power at FOH is possibility.

JP
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Rob Spence

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Re: QRX 212/75 Problem - Big Problem
« Reply #27 on: April 06, 2012, 04:24:11 pm »


We've used 6 Growlers center clustered on a PL6 with 2 Qrx212/75s a side, it was just about right. You could conservatively equate a Growler to 1.5 x 18, so with coupling, we had 4 218s, roughly. Depends on the style and venue of course for your needs.

Mike
So, to amplify, a pair of QRX212 would over run a single 2x18. I would have a pair of 2x18s per side if I were running 2 QRX per side.
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Rob Spence

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Re: QRX 212/75 Problem - Big Problem
« Reply #28 on: April 06, 2012, 04:27:32 pm »

Cutting power to the amps shouldn't result in blowing speakers. The output relays of the DR260 should open. However, applying phantom power to a wide-open mic could cause this or loosing power at FOH is possibility.

JP
The relays "should" open but before the mechanical parts get moving, a pop could get through and the amps would still have plenty of power to do it. I have lost 12" drivers (not in my QRX) before when an unauthorized person powered things down in the wrong order. Some gear put out a nasty pop when powered off.
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Tim Perry

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Re: QRX 212/75 Problem - Big Problem
« Reply #29 on: April 06, 2012, 04:48:18 pm »

I am not familiar with the amp you are using on the mids. Is there more info on the model? I use a QSC PLX3402 on my mids - one cabinet per channel.
Where are the gains on the amp set? I prefer to leave mine wide open or clockwise so if someone were to change something, the most would be it would get quieter.

Operating the power amps at maximum gain maximizes the ratio between the 'pop" and the signal. 

Turn the driverack outputs up and the amp attenuators down. It will still pop when powered off but wont be nearly as speaker destroying. 

 
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Re: QRX 212/75 Problem - Big Problem
« Reply #29 on: April 06, 2012, 04:48:18 pm »


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