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Author Topic: Advice on QSC Amps  (Read 1968 times)

Allen Smith

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Advice on QSC Amps
« on: August 03, 2015, 05:17:30 pm »

I recently returned to the music business after an almost 20 year hiatus.  Wow things have changed.  What hasn't changed is my equipment addiction. 

I have purchased 4 QRX 212 tops and 8 EAW LA118 subs.  I ended up with 118s instead of 128s because I was going to 'keep it small'.  Well that didnt work out so well.

I have 2 PLX3402 that I am bridging into 4 of the subs, 2 on each.  I need to power them all and I am looking at the PL380.  Without looking at space, cost or weight considerations and only evaluating them sonically, am I better off to add 2 more PLX3402 bridged into the additional 4 118s or use a PL380 to power all 8 subs with a stereo 2 ohm load.  I have read people are using the PL380 in this mode with good success.  The PL380 would be 8,000 total watts and the 4 bridged PLX3402 would be about 15k total but I have read where some folks are not huge fans of the PLX3402 bridged at 4 ohms into subs.  I have done a couple gigs with the 2 PLX3402 bridged into the 4 subs and I was not overwhelmed with the setup.

So again my question, 2 more PLX3402 or a single PL380 to do it all.  As a side note, I can use the current PLX3402 on the twelves instead of subs if I get the PL380.
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boburtz

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Re: Advice on QSC Amps
« Reply #1 on: August 03, 2015, 06:02:47 pm »

So again my question, 2 more PLX3402 or a single PL380 to do it all.  As a side note, I can use the current PLX3402 on the twelves instead of subs if I get the PL380.
We use PL380s on subs. We use them stereo with four ohm loads and two ohm loads. They are great amps for subs in both situations. The 3402 is perfect for the 12's on the QRX. Use one amp per pair, then get another amp to run all four horns. that, with a PL380 on your subs, and you've got a great little PA.
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Stephen Kirby

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Re: Advice on QSC Amps
« Reply #2 on: August 03, 2015, 07:08:28 pm »

IME the PLX don't like low loads.  They also don't like saggy power.  I think the full on Power Light series are more robust.  When I was buying a new sub amp, it was between the PL 6 and a Crest Pro9200 which I ended up with for the weight.  Both ran away from a bridged 3402 even at lower levels.
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boburtz

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Re: Advice on QSC Amps
« Reply #3 on: August 03, 2015, 07:50:18 pm »

IME the PLX don't like low loads.  They also don't like saggy power.  I think the full on Power Light series are more robust.  When I was buying a new sub amp, it was between the PL 6 and a Crest Pro9200 which I ended up with for the weight.  Both ran away from a bridged 3402 even at lower levels.
We used to use PL6 on subs and ended up moving to the 380s for weight savings. I didn't realize a difference in performance on the subs, meaning the weight savings didn't compromise the output. 

Side note; after noticing that the 50a rac-pac in one of my FOH amp racks was miswired (!), I found that the two 30a outlets that the 380s were plugged into were actually wired to 20a breakers (two 20a outlets were wired to 30a breakers, I bought this unit from Ampshop.com and it came that way). It had been running this way for about a year. We had run the 380s with two 4ohm subs per channel MANY times and never tripped the 20a breaker. It seems to me that the PL380 is a pretty efficient little amp.
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Allen Smith

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Re: Advice on QSC Amps
« Reply #4 on: August 04, 2015, 01:33:57 pm »

We used to use PL6 on subs and ended up moving to the 380s for weight savings. I didn't realize a difference in performance on the subs, meaning the weight savings didn't compromise the output. 

Side note; after noticing that the 50a rac-pac in one of my FOH amp racks was miswired (!), I found that the two 30a outlets that the 380s were plugged into were actually wired to 20a breakers (two 20a outlets were wired to 30a breakers, I bought this unit from Ampshop.com and it came that way). It had been running this way for about a year. We had run the 380s with two 4ohm subs per channel MANY times and never tripped the 20a breaker. It seems to me that the PL380 is a pretty efficient little amp.

Thanks to both of you for the feedback.  I think I will go with the PL380 on subs, the PLX3402s on mids and TBD on the horns.  This decision prompts a couple new questions.  Should I be concerned with the age of the PLX3402 and capacitor issues?  Has anyone replaced the capacitors in these amps and have an idea how much I should expect that repair to cost?

For the horns I need an amp that will run 2 drivers on each channel at a 4 ohm load.  I am looking at the PLX 1104 or the PLX1802.  Both have the same approximate output at 8 ohms and 4 ohms.  I like the light weight and reduced size of the 1104 and for horn drivers it looks like it is very robust.  The PLX1802 has a better feature set but higher cost and heavier weight.  I don't ever anticipate using this amp on anything other than the horn application since it would be too small for much of anything else.

Is there any compelling reason I may not have thought of to pay more and carry more and purchase the 1802 over the 1104?

Thanks again for all of your feedback, it is very helpful.
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Mike Diack

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Re: Advice on QSC Amps
« Reply #5 on: August 04, 2015, 05:19:39 pm »

Should I be concerned with the age of the PLX3402 and capacitor issues?  Has anyone replaced the capacitors in these amps and have an idea how much I should expect that repair to cost?
Thanks again for all of your feedback, it is very helpful.
I have had a long and happy relationship (both as a user and local service agent) with PLX3402s for as long as they have existed (16 years!) and have not noticed any capacitor issues with them other than the odd one with the big reservoir caps breaking off due to bad handling. These amps should always be rear supported as otherwise the board can flex, and this can cause one particular diode to break, which can cause a chain reaction catastrophic failure under subsequent heavy use. Very early ones (98/99) had ribbon cable issues. Good medum sized amps.
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Allen Smith

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Re: Advice on QSC Amps
« Reply #6 on: August 06, 2015, 07:27:10 pm »

I have had a long and happy relationship (both as a user and local service agent) with PLX3402s for as long as they have existed (16 years!) and have not noticed any capacitor issues with them other than the odd one with the big reservoir caps breaking off due to bad handling. These amps should always be rear supported as otherwise the board can flex, and this can cause one particular diode to break, which can cause a chain reaction catastrophic failure under subsequent heavy use. Very early ones (98/99) had ribbon cable issues. Good medum sized amps.
Mike,  thanks for sharing your thoughts.  I think I will keep the 3402 around.  I always rear rack rail amps.
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Rob Spence

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Re: Advice on QSC Amps
« Reply #7 on: August 07, 2015, 12:41:03 am »

I have a bunch of 3402s. Love em.

I use a pair of them for the 12s in my QRX212s with a PLX1602 doing the horns.
Most of the time it runs as a dual mono rig (stereo to some of you). Sometimes I add a 1804 and run as a dual pa.


Sent from my iPad using Tapatalk HD
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Re: Advice on QSC Amps
« Reply #7 on: August 07, 2015, 12:41:03 am »


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