strange sound coming from amp

[perfecxionX 10+ year member]

im getting a weird noise coming from my sub. its a fan like noise, or maybe something like running water. but as i turn the gain up the sound gets louder. i have to turn music all the way down to hear it. im not overpowering the sub or pushing the amp too hard; with music off the sound is audible with gain half way. its not a box problem, im sure the sounds coming from the sub. theres no visible damage to the sub, and the manufacturer thinks that this sound is being produced by the amplifier.

has anyone ever heard of a problem like this?

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[thch 10+ year member]

sure, what amplifier?

in class D amps, issues with the output filter can allow switching noise to reach the speaker. while such noise normally is at high frequencies, intermodulations can be pushed back to the audiable range.

in class AB amps, a long wire run introduces significant capacitance which adds maybe a 1 microsecond delay. while this doesn't seem like much, the amp may still have a gain at 1MHz, and thus the delay causes the amp to perpetually overcorrect. this RF noise will again move to audible ranges, as well as quickly heat up the amp!

there are a few other things that can do this. power supply noise getting into the signal for one, as well as interference.

 

[perfecxionX 10+ year member]

its a phoenix gold qx900 (mono). they got discontinued like 3-4 years ago, but the amp was just bought as brand new. it really doesnt bother me, i just dont want to damage anything.

thanks