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Power Amp Losing volume?

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Thomas Le:

--- Quote from: Paul G. OBrien on September 18, 2022, 05:53:25 PM --- Simply disconnecting and reconnecting the wire may have "fixed" the problem (if it is corrosion), a test for this would be to now reconnect the wire to the original channel.. if the signal level is back to where it should be then you have confirmation.

--- End quote ---

I'll see if I can check sometime this saturday.


--- Quote from: John Roberts {JR} on September 19, 2022, 11:20:19 AM ---If the upper rail of class g/h amp is not working the gain will be the same, but it will clip sooner. This may be audible in full tilt use, but not obvious for normal listening levels.  +1 missing one leg of differential source could look like -6dB loss.

JR

--- End quote ---

I did check for any loose wiring, they were tightly screwed in.

Craig Hauber:

--- Quote from: Thomas Le on September 19, 2022, 04:17:11 PM ---I'll see if I can check sometime this saturday.

I did check for any loose wiring, they were tightly screwed in.

--- End quote ---
I use a lot of CX series in my portable rigs and the attenuator pots get dirty (or something)  When I now experience an imbalance the first thing I do is to exercise the pot a bit and it usually clears up the problem.
It will pass signal but at a significantly reduced level.

Just my personal experience with repurposed CX series amps that lived their previous lives in 24-7-365 always-on installs

Brian Jojade:

--- Quote from: Thomas Le on September 17, 2022, 04:38:42 PM ---Story time:

Fortunately the way the system was spec'd,  the installer only used one amp, one channel per side, so there's two amps for FOH speakers, and I was able to switch to channel 2 on the amp.

--- End quote ---

So you're saying that 2 of the amp channels simply aren't being used?  Or are the amps in BRIDGE mode?

If the installer put in the amps and only used half of the amp, that's a pretty silly waste of money for the design, but handy for you now.  If switching to channel 2 on the amp fixed it, then who cares about fixing the first side?

Or, you can move everything over to the 2nd amp and pull out the problem unit to put on the bench for testing and repair.

Thomas Le:

--- Quote from: Brian Jojade on November 29, 2022, 04:13:03 PM ---So you're saying that 2 of the amp channels simply aren't being used?  Or are the amps in BRIDGE mode?

If the installer put in the amps and only used half of the amp, that's a pretty silly waste of money for the design, but handy for you now.  If switching to channel 2 on the amp fixed it, then who cares about fixing the first side?

Or, you can move everything over to the 2nd amp and pull out the problem unit to put on the bench for testing and repair.

--- End quote ---

Nope its not in bridge mode, yeah its a weird spec, buying two amps but only using one channel. This was before my time so I don't know. Yeah I was meaning to get around to noodling with it but I didn't have time haha and "if it ain't broke" mentality so I just left it there...

Eventually I did a proposal to upgrade to all Crown CDi Drivecore (the one with the screen) so that it can be network manageable. We'll see how that goes...

doug johnson2:
I don't have a lot of time with the CX amps but, have delt with the MX series.  I have had issues similar to this that were the result of problems volume pots.  Cleaning and exercising them may or may not temporarily fix the issue but, if it went away, it would come back in short order.  IIRC, it was a known issue and QSC offered a replacement kit long after the MX series were discontinued.

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