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Title: QSC PLX3602 driving subs.....not working well!!
Post by: Dave Batistig on November 18, 2012, 11:30:21 AM
I have a problem with my 2 PLX3602 that I hope you all can shed some light on.

First the specifics:

Running four (4) Peavey QW 218 subs, powering 2 of these with bridged 3602's, the other two with bridged Peavey CS3000's.

Played a smaller room last night and only used 1 sub per side. Initially was running the subs of of the 2 PLX3602s and there was no low end. The kick drum sounded all "100-125" hz. No thump...sounded like pounding on a KFC bucket!!! Switched to the CS3000s and was rattling the walls with the subs!!!

The 3602s are in bridge mode, with the switches set to full range on the back...no need for the internal crossover, we cross these subs at either 125 or 140hz, depending on the room.

One of the 3602s is brand new...just bought it. They both are exhibiting this behavior!

Thoughts??

Thanks!!

Dave
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Jonathan Betts on November 18, 2012, 11:41:29 AM
Try lowering the crossover point to 90Hz. What are you using for a crossover? Are your cables set up for bridge mode? Are you using any kind of limiting to protect your speakers?
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Ivan Beaver on November 18, 2012, 12:02:35 PM
I have a problem with my 2 PLX3602 that I hope you all can shed some light on.

First the specifics:

Running four (4) Peavey QW 218 subs, powering 2 of these with bridged 3602's, the other two with bridged Peavey CS3000's.

Played a smaller room last night and only used 1 sub per side. Initially was running the subs of of the 2 PLX3602s and there was no low end. The kick drum sounded all "100-125" hz. No thump...sounded like pounding on a KFC bucket!!! Switched to the CS3000s and was rattling the walls with the subs!!!

The 3602s are in bridge mode, with the switches set to full range on the back...no need for the internal crossover, we cross these subs at either 125 or 140hz, depending on the room.

One of the 3602s is brand new...just bought it. They both are exhibiting this behavior!

Thoughts??

Thanks!!

Dave
Did you have channel 2 turned all the way down?  If channel 2 is turned up-it will do some "weird things" on QSC amps when in bridged mode.   
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Mac Kerr on November 18, 2012, 12:12:39 PM
I have a problem with my 2 PLX3602 that I hope you all can shed some light on.

First the specifics:

Running four (4) Peavey QW 218 subs, powering 2 of these with bridged 3602's, the other two with bridged Peavey CS3000's.

Played a smaller room last night and only used 1 sub per side. Initially was running the subs of of the 2 PLX3602s and there was no low end. The kick drum sounded all "100-125" hz. No thump...sounded like pounding on a KFC bucket!!! Switched to the CS3000s and was rattling the walls with the subs!!!

The 3602s are in bridge mode, with the switches set to full range on the back...no need for the internal crossover, we cross these subs at either 125 or 140hz, depending on the room.

One of the 3602s is brand new...just bought it. They both are exhibiting this behavior!

Thoughts??

Thanks!!

Dave

Check your wiring. You should be coming off the binding post outputs, using the 2 red posts, with the hot conductor on ch1. It sounds like you may have plus and minus switched on one of the amps.

Also, use the sub crossover in the amps or lower the crossover point in your existing crossover. 80Hz-100Hz may be better than 125-140.

Mac
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Scott Carneval on November 18, 2012, 12:22:40 PM
I think your real problem is you're running the amps at two ohms bridged, which they're neither rated for nor capable of.  Those QW218 cabs are 4ohms nominal, so two of them would present a 2ohm load to your amp.  Run it in stereo is the only way.
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Jonathan Betts on November 18, 2012, 12:29:48 PM
I believe the op was running one cabinet per amp. IMO performance would be just as good running 2 cabinets in stereo.
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Mac Kerr on November 18, 2012, 12:36:47 PM
I think your real problem is you're running the amps at two ohms bridged, which they're neither rated for nor capable of.  Those QW218 cabs are 4ohms nominal, so two of them would present a 2ohm load to your amp.  Run it in stereo is the only way.

There is one amp per speaker, and the 3602 is rated into 4Ω bridged. In the Peavey product literature the QW218 is listed as 8Ω.

I am not a fan of relying on bridged amps, in part because they require different speaker wiring, but in this case, if wired correctly they should work.

Mac
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Conrad Muzoora on November 18, 2012, 12:42:36 PM
I have run QSC powerlight amps for a long while, later replaced them with qsc rmx amps on the subs. My impression is that powerlight will drive the subs fine, only if you can feed them with solid power, where as the old heavy iron with caps will work somewhat better on less than ideal power. If the power is solid, check your connections, something may be wrong there.

Conrad
www.kooleventug.com
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Jonathan Betts on November 18, 2012, 12:50:09 PM
There is one amp per speaker, and the 3602 is rated into 4Ω bridged. In the Peavey product literature the QW218 is listed as 8Ω.

I am not a fan of relying on bridged amps, in part because they require different speaker wiring, but in this case, if wired correctly they should work.

Mac


The cabinet presents a 4 ohm load with both drivers running.
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Mac Kerr on November 18, 2012, 01:00:27 PM


The cabinet presents a 4 ohm load with both drivers running.

Ah yes, I misread the spec. I missed the (each driver) in brackets. In either case the amp is rated into that impedance. The problem the OP described does not sound like the speaker impedance is the problem.

Mac
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Tim Tyler on November 18, 2012, 01:11:52 PM
Dave -

The QW218 sub is factory wired as 2 x 8 ohm speakers seperately wired to the nl4/nl8 connector with the bottom driver wired to 1+- and the top driver wired to 2+-.  Unless the box has been internally rewired to parallel the drivers, you must use a 4-wire speaker cable to get performance from both drivers.

I agree with earlier comments about your issue being one of proper wiring.  Reversed polarity within the box, from the amp to the box and/or between boxes should be considered as problem areas.  A bridged 3602 will give plenty of performance, if properly deployed.

-Tim T
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Joe Jordan on November 18, 2012, 08:44:42 PM
i'm currently using a PLX 3602 Bridged driving a pair of SRX 718. The only issue I've had is getting enough power to them. As long as the AC is solid there is plenty of "thump"
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Mac Kerr on November 18, 2012, 09:14:56 PM
The QW218 sub is factory wired as 2 x 8 ohm speakers seperately wired to the nl4/nl8 connector with the bottom driver wired to 1+- and the top driver wired to 2+-.  Unless the box has been internally rewired to parallel the drivers, you must use a 4-wire speaker cable to get performance from both drivers.

I agree with earlier comments about your issue being one of proper wiring.  Reversed polarity within the box, from the amp to the box and/or between boxes should be considered as problem areas.  A bridged 3602 will give plenty of performance, if properly deployed.

If the OP is using the ch1 NL4 on the amp, which has both channels on it, and is using a 4 wire NL4 cable, putting the amp in bridged mode will drive the 2 speakers in the box out of polarity. We don't know that polarity is the problem, but until the OP comes back with more info it's about all we've got.

Mac
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Jonathan Betts on November 18, 2012, 09:59:32 PM
i'm currently using a PLX 3602 Bridged driving a pair of SRX 718. The only issue I've had is getting enough power to them. As long as the AC is solid there is plenty of "thump"

Have you tried running the 718's in stereo? They will perform just as well and last much longer.
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Stu McDoniel on November 18, 2012, 11:27:35 PM
I have a problem with my 2 PLX3602 that I hope you all can shed some light on.

First the specifics:

Running four (4) Peavey QW 218 subs, powering 2 of these with bridged 3602's, the other two with bridged Peavey CS3000's.

Played a smaller room last night and only used 1 sub per side. Initially was running the subs of of the 2 PLX3602s and there was no low end. The kick drum sounded all "100-125" hz. No thump...sounded like pounding on a KFC bucket!!! Switched to the CS3000s and was rattling the walls with the subs!!!

The 3602s are in bridge mode, with the switches set to full range on the back...no need for the internal crossover, we cross these subs at either 125 or 140hz, depending on the room.

One of the 3602s is brand new...just bought it. They both are exhibiting this behavior!

Thoughts??

Thanks!!

Dave
The QSC is a switching power amp design.  What is your AC setup for your amps?
A good AC feed is a probably a good start.
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Bob Leonard on November 19, 2012, 12:15:38 AM
I have a problem with my 2 PLX3602 that I hope you all can shed some light on.

First the specifics:

Running four (4) Peavey QW 218 subs, powering 2 of these with bridged 3602's, the other two with bridged Peavey CS3000's.

Played a smaller room last night and only used 1 sub per side. Initially was running the subs of of the 2 PLX3602s and there was no low end. The kick drum sounded all "100-125" hz. No thump...sounded like pounding on a KFC bucket!!! Switched to the CS3000s and was rattling the walls with the subs!!!

The 3602s are in bridge mode, with the switches set to full range on the back...no need for the internal crossover, we cross these subs at either 125 or 140hz, depending on the room.

One of the 3602s is brand new...just bought it. They both are exhibiting this behavior!

Thoughts??

Thanks!!

Dave

Because both are cabled incorrectly. Buy some banana jacks and wire your cables with the banana jacks to the amp and NL4 to the speakers using pins 1+/1-. Make sure your DIP switches are set correctly, and make sure that channel 2 sensetivity is turned to off.
 
The 3602 is not my choice for subs but when properly powered the amp will work fine. The problems I found years ago, and discussed at length here, were heat and sensetivity issues to low power, both of which can be show stoppers. I swapped my 3602s from powering my subs to powering my 725s, then replaced them all with 4050HDs for tops and subs in my dual system. I have not had a problem since other than a heavy rack. My 3602s now run vocals and monitors only. Not bridging your amps will actually give you better sound and reliability, so you might try running your speakers in stereo mode, you might just like what you hear.  ;) 
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Dave Batistig on November 19, 2012, 11:11:19 PM

Because both are cabled incorrectly. Buy some banana jacks and wire your cables with the banana jacks to the amp and NL4 to the speakers using pins 1+/1-. Make sure your DIP switches are set correctly, and make sure that channel 2 sensetivity is turned to off.
 
The 3602 is not my choice for subs but when properly powered the amp will work fine. The problems I found years ago, and discussed at length here, were heat and sensetivity issues to low power, both of which can be show stoppers. I swapped my 3602s from powering my subs to powering my 725s, then replaced them all with 4050HDs for tops and subs in my dual system. I have not had a problem since other than a heavy rack. My 3602s now run vocals and monitors only. Not bridging your amps will actually give you better sound and reliability, so you might try running your speakers in stereo mode, you might just like what you hear.  ;)

Thanks to everyone for the input. I will double check the wiring. I am using 4 conductor cable wired to the binding posts, then to  4 conductor speakon connectors mounted in a patch bay. I will make sure all these are wired correctly. With the way the subs sound...a phase issue makes the most sense!!

Thanks!

Dave
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Dave Batistig on November 19, 2012, 11:21:25 PM
Dave -

The QW218 sub is factory wired as 2 x 8 ohm speakers seperately wired to the nl4/nl8 connector with the bottom driver wired to 1+- and the top driver wired to 2+-.  Unless the box has been internally rewired to parallel the drivers, you must use a 4-wire speaker cable to get performance from both drivers.

I agree with earlier comments about your issue being one of proper wiring.  Reversed polarity within the box, from the amp to the box and/or between boxes should be considered as problem areas.  A bridged 3602 will give plenty of performance, if properly deployed.

-Tim T

To be more specific with how I "think" I have the rack wired....

I have +1 and +2 twisted together and on the Positive binding post, and -1 and -2 twisted together and on the negative binding post. This then feeds a 4 conductor speakon connector in the patch panel. There are a total of 4 speakon connectors like this in the patch panel for the subs....one wired to each amp.
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Dave Batistig on November 19, 2012, 11:48:31 PM
The QSC is a switching power amp design.  What is your AC setup for your amps?
A good AC feed is a probably a good start.

almost all the clubs we play have a dedicated 240V line for the bands...my whole PA runs off my distro, so power insn't typically an issue, and wasn't at this last gig. The Peavey CS3000s performed flawlessly. It looks like it is a wiring issue, with the way the subs sounded, it sounds like a phasing issue. I will double check the wiring.
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Tim Perry on November 20, 2012, 12:23:34 AM
To be more specific with how I "think" I have the rack wired....

I have +1 and +2 twisted together and on the Positive binding post, and -1 and -2 twisted together and on the negative binding post. This then feeds a 4 conductor speakon connector in the patch panel. There are a total of 4 speakon connectors like this in the patch panel for the subs....one wired to each amp.


can you post a picture?

If i understand this description you need to move the wires from the negative terminal to the unused positive terminal for bridged operation.
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Mac Kerr on November 20, 2012, 12:41:52 AM
To be more specific with how I "think" I have the rack wired....

I have +1 and +2 twisted together and on the Positive binding post, and -1 and -2 twisted together and on the negative binding post. This then feeds a 4 conductor speakon connector in the patch panel. There are a total of 4 speakon connectors like this in the patch panel for the subs....one wired to each amp.

When you say "Positive binding post" and "Negative binding post", what do you mean? If you mean the posts from ch 1, that is wrong. The 1+ and 2+ should be on the red binding post of ch1, the 1- and 2- should be on the red binding post of ch2. putting banana plugs on the wires will make it easier to deal with issues.

I would double check the wiring, because your symptoms could be the result of miss wiring here.

Mac
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Tim Tyler on November 20, 2012, 02:23:09 PM
When you say "Positive binding post" and "Negative binding post", what do you mean? If you mean the posts from ch 1, that is wrong. The 1+ and 2+ should be on the red binding post of ch1, the 1- and 2- should be on the red binding post of ch2. putting banana plugs on the wires will make it easier to deal with issues.

I would double check the wiring, because your symptoms could be the result of miss wiring here.

Mac

This is a solution to the wiring, assuming the NEW boxes are wired as standard Peavey.  OP could also use an NL4 connector into the A Speakon output with the wires to the patch plate connected to the 1+ and 2+ posts (bridged).  I would check the wiring of the original boxes, it looks like someone may have paralleled the drivers in the  box.

-Tim T
Title: Re: QSC PLX3602 driving subs.....not working well!!
Post by: Bob Leonard on November 20, 2012, 06:21:25 PM
We can put an end to the speculation easily.

OP, assuming that you are running this amplifier in bridged mode please perform the following tasks.

1. Purchase a banana jack.

**Prior to the next step remove the NL4 from one end of a speaker cable. This cable will run to the first sub closest to the amplifier.

2. Attach the banana jack to the end of the speaker speaker cable where the NL4 used to be. The jack will have a hump on one side, this is considered and marked as the negative side on most banana jacks.

**When performing the following step you will use a DVM or continuity tester to confirm that you are attaching the correct wire to the correct connection on the banana jack.

3. Attach the wire running to the NL4 -1 connection to the negative side of the banana jack.

4. Attach the wire running to the NL4 +1 connection to the positive side of the banana jack.

5. DO NOT attach any other wires leading to the NL4 to the banana jack. If additional wires exist fold them back and insulate them from the banana jack and from each other.

6. set the 3602 to bridged mode using the switch on the back. (refer to photo)

7. Turn the channel #2 sensetivity knob on the front of the amplifier to OFF. (full clockwise)

8. Plug the banana jack into the two (2) RED binding posts located on the back of the 3602. Note that the posts are clearly marked + and -. Be sure that the negative side of the banana jack is plugged into the post marked negative. (refer to photo)

9. Run a standard NL4 to NL4 speaker cable to the second speaker from the first speaker. A pair of 8 ohm speakers run in series will now have an impedence of 4 ohms.

10. Any combination of cabinets that lowers the impedence below 4 ohms must be run using a stereo configuration as the amplifier is not rated for 2 ohm operation in bridged mode. (refer to photo)
 
If all else fails RTFM or call QSC. Good luck, and I hope this helps.