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Power Amp Losing volume?

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Thomas Le:
Story time:

Got an amp rack that has 4 QSC CX that are 22 years old. Just got a notification from one of the pastors on friday that the "volume was not as loud as it used to be". My thinking was that one of the main amps finally gave up and bit the magic dust. Upon inspection, all 4 are turning on still working, but after some testing and going back and forth from the amp rack room, I'm guessing one of the channels is giving a lower output even though nothing has changed in DSP land and the attenuators are at full tilt. 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. Obviously given the age, I am "working my way up the chain" on trying to get them replaced with CDi Drivecore equivalents.

The stupid question: based on this experience, can a power amplifier lose it's output/volume over time?

John Roberts {JR}:

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

Got an amp rack that has 4 QSC CX that are 22 years old. Just got a notification from one of the pastors on friday that the "volume was not as loud as it used to be". My thinking was that one of the main amps finally gave up and bit the magic dust. Upon inspection, all 4 are turning on still working, but after some testing and going back and forth from the amp rack room, I'm guessing one of the channels is giving a lower output even though nothing has changed in DSP land and the attenuators are at full tilt. 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. Obviously given the age, I am "working my way up the chain" on trying to get them replaced with CDi Drivecore equivalents.

The stupid question: based on this experience, can a power amplifier lose it's output/volume over time?

--- End quote ---
Generally no with modern solid state amps and 22 YO is modern solid state...   Are they getting unusually hot? Are speaker loads in good shape?

JR

Thomas Le:

--- Quote from: John Roberts {JR} on September 17, 2022, 04:58:10 PM ---Generally no with modern solid state amps and 22 YO is modern solid state...   Are they getting unusually hot? Are speaker loads in good shape?

JR



--- End quote ---

I'll admit the amp room temperature varies wildly because it does not have good Air Conditioning flow but it does not get hot. Speakers themselves are ok once I switched over to the other channel, nothing has changed on the speaker side, all original drivers, nothing blown.

John Roberts {JR}:

--- Quote from: Thomas Le on September 17, 2022, 05:07:53 PM ---I'll admit the amp room temperature varies wildly because it does not have good Air Conditioning flow but it does not get hot. Speakers themselves are ok once I switched over to the other channel, nothing has changed on the speaker side, all original drivers, nothing blown.

--- End quote ---
The amps could be tired... Loose power transistor screws could overheat leading to a soft shut down. Air flow blocked by 22 years of dust could compromise cooling.

Shorted speaker wires could cause problems, but generally failure is not graceful, more severe.

I am not familiar with innards of the CX but some amps have clip limiting that would fold back amp level/gain in case of current limiting or thermal overload.

JR

Bob Taylor:
If the Amp is down just a bit, like 6 dB, are all the inputs on the Balanced interface making connections on both Pos and Neg? And this means at the processor also. Wiggle stuff, re insert, even open up the amp and Re Seat Ribbon connectors? Flip the input/mono switches a few times to break the 22 years of corrosion.

Not played with this amp, but at first read i say it is a corroded jack or........

Bob T

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