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Author Topic: qsc plx amps  (Read 8037 times)

Gareth James

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qsc plx amps
« on: December 18, 2004, 07:01:12 pm »

Can anyone tell me how reliable a PLX1602 would be operating into a 4ohm mono bridge mode to power a sub?
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ChainedDragon

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Re: qsc plx amps
« Reply #1 on: December 18, 2004, 11:54:43 pm »

should run just great


They'll run fine in 2ohms even, as long as you dont push them to hard
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Weogo Reed

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Re: qsc plx amps
« Reply #2 on: December 19, 2004, 11:32:22 am »

Hi,

To clarify:

"They'll run fine in 2ohms even, as long as you dont push them to hard"

Note, the original post said 4 ohms BRIDGED.
This is the same to the amp as running 2 ohms STEREO.

The PLX2602 will NOT do 2ohms BRIDGED.  Very few amps will.

For long life, I would not push the 1602 hard at either 4 ohms bridged or 2 ohms stereo.

Good health,  Weogo
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Gareth James

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Re: qsc plx amps
« Reply #3 on: December 19, 2004, 01:49:22 pm »

So whats the deal? How can i get enough power (~1600W) into my 4ohm sub? I cant afford crown MA's!!
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Mike MacWillie

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Re: qsc plx amps
« Reply #4 on: December 19, 2004, 02:55:01 pm »

The plx should be fine at 4 ohms bridged.. You could also use an rmx 1850HD, it was built to run at 4 ohm bridge all day long.. and It'll give you 1800 watts @ 4 ohm bridged.
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Evan Kirkendall

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Re: qsc plx amps
« Reply #5 on: December 19, 2004, 09:11:49 pm »

I dont see why you would have any problems running the amp at 4 ohms bridged. QSC has a great reputation and I havent seen many of their amps fail, even under some of the worst conditions.
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bgavin (Bruce Gavin)

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Re: qsc plx amps
« Reply #6 on: December 20, 2004, 10:16:56 am »

The RMX 1850HD is specifically optimized for 2 ohm stereo operation.  It has larger heat sinks for this severe load.  The downside is the 43-odd pounds, instead of 21 pounds for the PLX.  The 1850HD is less expensive though.
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Mike {AB} Butler

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Re: qsc plx amps
« Reply #7 on: December 23, 2004, 02:02:42 pm »

kaisersoze wrote on Sat, 18 December 2004 16:01

Can anyone tell me how reliable a PLX1602 would be operating into a 4ohm mono bridge mode to power a sub?


As a PLX owner who has used a 1602 many times for sub duty, I can tell you that the amp works great at 4 ohms bridged, and is VERY reliable - first amp I ever took a chance to run that hard, and it delivered! I can also say that 1600W on subs is barely enough for even small gigs; more is better.
Some people don't like the PLX on subs, but I think they're just fine.
Regards,
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Tim Padrick

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Re: qsc plx amps
« Reply #8 on: December 23, 2004, 09:45:09 pm »

My choice would be a used K2 (about 2400w bridged into 4 Ohms, 38 pounds, $800-ish on eBay) if you can conveniently add a bit of forced air cooling to your rack.  

Gareth James

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Re: qsc plx amps
« Reply #9 on: December 24, 2004, 09:13:46 am »

Well i get the impression either the RMX1850HD or PLX1602 is the way to go since i dont want to have to mod my amp rack for extra cooling.

There are a couple of things im still not clear on however. A no. of posts are telling me 1600W is not enough for subs, doesnt that depend on the sub?! Apart from this im going to be running this amp real hard as it will be used occasionally for a drum and bass night. If im exceeding the long term capabilities of my drivers im surely not going to get more sound because of power compression and probably running the risk of voice coil failure?

Also isnt running at 2400W compared to 1600W only an inaudible 1.5dB rise or are the equal loudness curves having some effect here?

OR will the music still have enough peaks (even when run through LMS compression) to stop full sine power getting through?

Excursion is not an issue here, the drivers are only pushing 20mm max at 750W with a >30mm max. This figure should be even lower with a steep rolloff just above this point.

Sorry to ramble on again but i want to get this as right as right can be!

Thanks to all who have lent their advice and shared the knowhow, its much appreciated!! Very Happy
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Gareth James

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Re: qsc plx amps
« Reply #10 on: December 27, 2004, 08:12:25 am »

um, i just had a look on the qsc website and on the rear view pic of the 1850HD the label says bridge mode: 8ohm min  Confused

Does this mean i wont be able to use it 4ohm or is the label wrong?
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John Roberts {JR}

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Re: qsc plx amps
« Reply #11 on: December 27, 2004, 10:32:16 am »

kaisersoze wrote on Mon, 27 December 2004 07:12

um, i just had a look on the qsc website and on the rear view pic of the 1850HD the label says bridge mode: 8ohm min  Confused

Does this mean i wont be able to use it 4ohm or is the label wrong?


I can't speak for QSC but I have seen similar cases where the agency testing ignores the owner's manual (which often doesn't exist at the time of testing) and is performed based on rear panel marking, while the product is offered for market use at the lower impedance. This is probably questionable, but I have seen it before.

In general you will get better life and reliability by not loading down "any" amp to 2 Ohms/ch. If you are planning to ride the amp hard and put it away wet, and maybe replace/upgrade after a few years, have at it.

I would also look to the owner's manual for clarification. If the owner's manual is the same as the backplate it's probably right. If they don't agree you should be able to get definitive clarification from QSC (they are a few times zones further away if they are working this week).

JR
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Mr.Nightro

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Re: qsc plx amps
« Reply #12 on: December 27, 2004, 10:34:52 am »

I am not sure where you where looking but if you go to the spec charts for the RMX series (on the QSC website) you would see that they have the RMX 1850HD rated at 1,800 watts in 4 ohms bridged. This amp was designed to & will handle the 4 ohm load easy all night as long as you stay out of the red, you CAN'T go wrong when you go with QSC. This was quoted directly from the QSC spec sheet "The RMX 1850HD provides improved thermal performance that gives you higher continuous power in 2-ohms stereo or 4-ohms bridged applications (a RMX 1850HD exclusive!)"

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Craig Leerman

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Re: qsc plx amps
« Reply #13 on: December 27, 2004, 01:39:32 pm »

Why not just jump up to the RMX 2450?  For the same weight as an 1850 and only about $100 bucks more, you get 1500w Bridged at 8 and 2400w bridged at 4.  I recently switched my sub amps over to 2450s. I'm using them on one system as bridged mono into 4 Ohms and on another system  as bridged mono into 8 Ohms with no problems.  The amps are cruising!

I have also used CX1102 (the install version of the PLX 3402) amps for subs at 4 ohms bridged with no problems, and some gigs were out here in the desert with ambient temps around 110 deg!  I recently turned all my CX1102 amps into mid amps and use the RMX 2450s exclusively on subs!  They are a little heavy, but then again I grew up moving old Peavey CS800s (I think they weighed about 3 pounds per watt) and Crown DC300s so a 2450 is not that bad to my old back!

Craig

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John Roberts {JR}

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Re: qsc plx amps
« Reply #14 on: December 27, 2004, 02:22:43 pm »

AFAIK the 1850 is just a 2450 running at a lower rail voltage to deliver output under heavy load for more time (higher duty cycle). The 2450 will deliver more peak power but for less time than an 1850 under similar conditions.

If your application is not overly demanding the 2450 may be a fine choice, the 1850 will be a little better choice for difficult applications.

JR
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Chris Van Duker

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Re: qsc plx amps
« Reply #15 on: December 27, 2004, 09:54:18 pm »

If you're looking at PLX amps for driving the LABsubs, you might want to look at the 2402. In addition to the couple extra dB of output, it actually draws a bit less power than the 1602 at 2ohms stereo (equiv. to 4 ohm bridged), 1/8 power. The 2402 is the lowest powered amp in the line to use Class H, which reduces both power consumption and heat.

-Chris
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Gareth James

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Re: qsc plx amps
« Reply #16 on: December 28, 2004, 11:46:23 am »

Thanks for everyones replies, think im gonna go with the RMX1850HD in the end, it sounds like a solid amp, which is exactly what i need. Cheers Very Happy
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Phil Pope

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how do they do it so cheap? (was Re: qsc plx amps)
« Reply #17 on: December 28, 2004, 02:18:14 pm »

had been thinking of getting one big amp to power four LABs (like a Crest PRO8200) but just found new QSC 1850HDs for $500 inc free shipping (although they may charge something for UK delivery).  With the exchange rate as it is at the moment I will end up spending less on the amps than I did on the drivers Smile  Thought I would be spending twice as much for some decent amps - what an xmas present!

Phil
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Phil Pope

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Re: how do they do it so cheap? (was Re: qsc plx amps)
« Reply #18 on: January 07, 2005, 12:29:03 pm »

forgot that US uses different voltage to UK Sad

The best price on a UK 240V model I have found is
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John Sincavage

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Re: qsc plx amps
« Reply #19 on: January 07, 2005, 02:37:16 pm »

Snow,
Check out the ce4000 by crown it accepts any voltage.
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Paul Magro

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Re: qsc plx amps
« Reply #20 on: February 08, 2005, 09:26:52 pm »

  I haven't read all the replies but will say that if you run the PLX into clip, it shuts down for a few seconds and then it kicks right back in.  As long as you don't do this it will run fine, but I cannot say if it will thermal out with such a load, in which the same thing will happen.  I had all my gear out except for a PLX 1602 and I ran it bridged into a 2 ohm load(two 2x15 subs) and after I set it so it wouldn't clip, it ran all night without a problem.  I'm not advocating this kind of use, but I was hooking up some friends for free and it was a good way to push the limits of the amp just to see what would really happen.
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Chris Van Duker

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Re: qsc plx amps
« Reply #21 on: February 09, 2005, 04:06:33 pm »

Quote:

 I haven't read all the replies but will say that if you run the PLX into clip, it shuts down for a few seconds and then it kicks right back in. As long as you don't do this it will run fine, but I cannot say if it will thermal out with such a load, in which the same thing will happen. I had all my gear out except for a PLX 1602 and I ran it bridged into a 2 ohm load(two 2x15 subs) and after I set it so it wouldn't clip, it ran all night without a problem. I'm not advocating this kind of use, but I was hooking up some friends for free and it was a good way to push the limits of the amp just to see what would really happen.


I think what you may have been seeing was the line voltage dipping so far that the amp reset itself. I've seen PLX amps go deep into clipping into a minimum impedance load without shutting down like that -- though I don't recommend doing that very often.

-Chris Van Duker
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