Help with a QSC CX254 amp

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Leroy Wiley

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Jul 13, 2020
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I have an X32 outputting to the QSC. What has been happening is that the main left speaker cuts out frequently, or never comes on at all. This has been going on for a few months. We had some sound pros come in and they maxed the QSC output controls and said that is how they run theirs and QSCs are kind of known for that. Of course, maxing the amp means the main slider on the X32 has to come way down. Anyway, that seemed to help some but only for a little while.

I have tried swapping the amp outputs so that the left feeds the right and vice versa. That makes the right speaker cut out. So I think that tells me the cable from the amp to the speaker is okay and that the speaker is okay. The problem is in the X32, QSC area.

I've been the church sound/video/streaming guy for a little over a year so I'm very green, but what amazes me is how the feeds into and out of the amp are stripped wire connections. I'm surprised everything isn't plugs and jacks. Is that normal? I would feel much better if I could have everything jacked and plugged - I would not worry so much about pulling out the amp and checking things. Stripped wire connections have got to be more problem-prone, right?

Any suggestions on how to proceed? Recommendations on how to set things up to make it much more stable? Online resources to guide me?

I've included an image of the inputs from the X32. The amp I'm talking about is the top amp in this photo. Those little green blocks are the inputs (actually input singular, that one little, stripped, white wire is feeding the bottom block, and that block is jumperred to the top block. The outputs are in the background and have covers over them (I think that's standard for this amp), but under the covers are stripped wire connections.

Edit: I forgot to mention if I move the input connections I can get the speaker to come back on sometimes, but not always. And sometimes the sound won't cut out all the way, but go way down instead.
 

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Euroblock connectors are widely used on permanent installation electronics as they are more reliable than "plugs and jacks" when terminated properly. The photo you've posted shows some very poorly done terminations. If your "sound pros" didn't flag that right away they the were less than pro.

If your amps have no or intermittent output when the attenuator is at different parts of it's rotation it's simply dirty. Rotating it quickly back and forth might clean it temporarily but the right answer is disassembly and cleaning followed by ensuring that the air supply to your electronics rack is filtered to prevent contamination. This is indeed a problem with QSC amps and with virtually every other brand of electronics that uses unsealed rotary pots. Using the attenuators to properly gain stage your sound system is the right approach when coupled with having the gear properly installed and maintained.
 
Riley Casey said:
Euroblock connectors are widely used on permanent installation electronics as they are more reliable than "plugs and jacks" when terminated properly. The photo you've posted shows some very poorly done terminations. If your "sound pros" didn't flag that right away they the were less than pro.

If your amps have no or intermittent output when the attenuator is at different parts of it's rotation it's simply dirty. Rotating it quickly back and forth might clean it temporarily but the right answer is disassembly and cleaning followed by ensuring that the air supply to your electronics rack is filtered to prevent contamination. This is indeed a problem with QSC amps and with virtually every other brand of electronics that uses unsealed rotary pots. Using the attenuators to properly gain stage your sound system is the right approach when coupled with having the gear properly installed and maintained.
Click to expand...
Thank you, Riley. Do you know where I can go to learn how to do the terminations properly? And how to clean and filter the amp? I will definitely try rotating it quickly back and forth.

What worries me about stripped wire type of connections is that the bare wire at the connection is exposed to wear and tear from any movement of the amp or cables and that over time they might break. From what you're saying though I'm guessing if it were properly terminated then breaking is not an issue.
 
Spinning the pot might fix the problem for a few minutes or days but its not a fix. Take it to an electronics tech and have the pots cleaned with Cramolin spray cleaner. Have the tech vacuum out the interior of the amp chassis as well. If the amp isn't in a closed rack with its own fan and fan filter cut a piece of AC filter foam to cover the fan inlet on the back panel and use velcro around the inlet to hold the foam. Clean the foam every month until you get a sense of how fast it's getting clogged with dust.

Moving the amp will certainly run the risk of breaking the cables at the connections. Permanent install amps are meant to be installed in a closed rack with all the wires tie wrapped to tie bars that run across the back of the rack to to support the cables. The amp should be in a case even if it does get moved. Simply install a back panel on the rack and install XLR input connectors and NL4 output connectors on that panel and connect those to the Euroblock terminals. A quick Google search for the term "dressing cables for Euroblock Connectors" turned up this and many more pages of hits. Pat and Brenda Brown know their stuff. Read and do what they say. Also get a copy of the Yamaha Sound Reinforcement Handbook.

www.prosoundtraining.com

Useful Tips for Using Euroblock Connectors Correctly

Pat Brown explains some peculiarities of Euroblock Connectors and gives some useful tips for using them correctly.
www.prosoundtraining.com
 
Couple of other things......first it looks like you are using an unbalanced line connection to the amp, you should look at wiring the connection from the mixer to the amp with a balanced line connection. Second it appears that you are running the amp in bridged mono between channels 1 2 and 3 4, to do that correctly you need to use the channel 1 input and the channel 3 input, only use the channel 1 and 3 level controls, turn down channel 2 and 4 level controls, make sure all the switch positions on the back of the amp are in the up position.

Also you need to find some real sound pros to call in the next time.
 
Thank you, Mike. Correct me please, but a balanced line is 3 conductors, one of which is ground, and the other two are feed/return conductors. Right? So coming out of our X32 is likely an XLR balanced line connection - 3 conductors (I don't have the X32 in front of me to check). But currently, I am only using the white conductor as input to the amp via a Euroblock.

You are saying I really should have all three conductors connected. I am going to assume if I trim back on that cable from the X32 I will find a black conductor in addition to the white one and the shield. So, looking at the back of my amp in the picture above it looks like the shield/ground should be connected to the rightmost pin of the Euroblock (rightmost as I look at the back of the amp
). Then the white to the positive (leftmost) and black to the negative (middle). Those are all questions, BTW.

That is your recommendation one sorted if I have that all straight.

Recommendation two is to feed channels 1 - 3 instead of 2 - 4 like it is now (the "pros" made that swap to 2 - 4 the last time they were out). And be sure all of the DIP switches are up. Is that DIP switch setting specific to the QSC CX254 or to QSCs in general and did you just know that off the top of your head?

Thanks again. You can tell by my questions that I do not know what I'm doing so I really do appreciate the help I get from here. Besides the Pro Sound Training link above, are there other resources online where I can learn more?
 
Judging by the picture the input wire looks to only be a single conductor and with a braid shield
around it . How the XLR connector is wired at the mixer should be checked out. Pin 2 on the XLR goes
to positve + , pin 3 on the XLR goes to negative - and xlr pin 1 goes to ground. sometimes the ground is disconnected
at the amp to clean up hum or grounding noise issues.

For an unbalanced input connection the way the amp is wired now would be correct.....depending how the connector at the mixer is wired. Use proper cable and wire it for a balanced input. How far away is the mixer from the amp.
There is no return on a balanced line connection, both the + and - carry audio signal of opposite polarity.
How a balance line system works is another topic all together.

Those dip switch settings are for the QSC CX series amps and yes I knew that, I use and set up many QSC's
 
For a short unbalanced run, it would be okay If the cable is just the one wire and a shield? The X32 is maybe five feet away from the amp (although the cable is about 10').

If you were going to redo this would you run a balanced connection to be on the safe side? Also, would you first connect the ground and listen for hum or grounding noise issues? Then disconnect the ground if there are issues?
 
Leroy Wiley said:
For a short unbalanced run, it would be okay If the cable is just the one wire and a shield? The X32 is maybe five feet away from the amp (although the cable is about 10').

If you were going to redo this would you run a balanced connection to be on the safe side? Also, would you first connect the ground and listen for hum or grounding noise issues? Then disconnect the ground if there are issues?
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If the equipment outputs and inputs are balanced I wire it up as a balanced connection even it their only 1 foot apart.

You need to look at bringing in better "professionals" to look at your system. Actually with just the sample that we have seen of your system you may to think about bringing someone in to look all of it over.
 
Thank you, Rob. That PDF is very good.

Thank you, Mike. I will wire it up balanced. We are in the sticks, 2 hours from a big city so my "pro" options are very limited. It's either the guys I brought in or see what it would cost to get someone from Tucson, 2 hours away. $$$

BTW, what occupational title would I search for to find a pro?

Edit: Contacted a pro in Tucson. I will probably set up a day with him/her soon.
 
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Leroy Wiley said:
Thank you, Mike. I will wire it up balanced. We are in the sticks, 2 hours from a big city so my "pro" options are very limited. It's either the guys I brought in or see what it would cost to get someone from Tucson, 2 hours away. $$$

BTW, what occupational title would I search for to find a pro?

Edit: Contacted a pro in Tucson. I will probably set up a day with him/her soon.
Click to expand...
Search for a specific job title would be hard and may not get great results.

Looking up legit audio production companies would be a good start, even if they do not do install service
chances are they know someone you could call.

Who or what company in Tucson did you call?
 
Mike Caldwell said:
Search for a specific job title would be hard and may not get great results.

Looking up legit audio production companies would be a good start, even if they do not do install service
chances are they know someone you could call.

Who or what company in Tucson did you call?
Click to expand...
azprosound.com

Arizona Pro Sound Inc. | Sound

Professional sound company delivering quality full production, touring, installations, and events for 40+ years
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