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negative terminal corrosion AND now amp's distorting and cutting out with new speakers

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i have a system that consists of a 12 volt 18 amp hour battery, a planet audio BB1200.4 class D 4 channel amp, a JBL GT5-15 sub in free air, and a battery tender charger. at first, i was using proel flash 8p mini PA speakers as mains, but tonight, i hooked up a brand new pair of JBL Northridge N26AW II speakers with 16 gauge wiring (because that's all the shop up the street had) and within an hour of listening at low levels, the amp started making a low level squealing sound, sort of like a buzzy digitally distorted high frequency kissing noise, even after i turned my media player off.

at the time, the sub was disconnected, but the wires were still in the amp, which shouldn't make a difference as the rear channel wasn't receiving a signal anyways as i also disconnected the rear ins i had split the left and right for with Y cables. when i'd used the proels, at first they were full range, but then i high passed them at 120Hz and low passed the sub at 120Hz too when i had that. until the issues started with the JBLs tonight, everything was 12 gauge. when i hooked the JBLs up, i switched the front channels back to full range, and was using 4 feet per side of 16 gauge for the new speakers.

after the first squealing incident, and checking that all of connections were both secure and that there were no shorts and the polarities were all correct, i started playing music again and within half an hour, the sound became intermittent, and the buzzing squeal returned.

after that, i tried to find out if it was possible for SPEAKERS to fry an amp... something i never heard of other than clipping an amp or running too low an impedance, but the JBLs are 8 ohms. that's when i read that supposedly frayed speaker wires can blow an amp. as the amount i stripped off the wires was too much for the amp's outputs, at first i curled the ends in on themselves so no exposed wire would be sticking out.

after reading that article, i went back and rewired the entire power system, except for the remote circuit, with 8 gauge wire with newly crimped O rings for the terminal as well as ditching the entire screw, nut & washers set that had corroded on the positive terminal with new ones as well as pulling the Y cables off and plugging my source directly into the front inputs. i also moved the power switch to only the remote circuit where before it controlled both that AND the positive terminal. as a side note, before that, the amp's led took a long time fading whenever i powered down, but now it blinks on an off instantly.

finally, regarding the corrosion, that was the circuit i was using with the original 12 gauge system i had no problems with until moving everything closer to where the JBLs are and hooking them up with the new 16 gauge wires.

when i listened to the proels, and also those with the sub, i used to connect my battery tender charger to offset the power drain while listening to music and disconnect it when i was done a few times, then started separate charging sessions when i was around to monitor the charger so as to mot overcharge the battery.

then, a few weeks ago, i noticed serious corrosion on both the terminal screw, nut and washers, along with nearly 1/2 an inch up the charger's alligator clips as well, and for a time, the charger stopped recognizing the battery when i reconnected it, until maybe after i brushed as much of the corrosion off as i could.

the last time i put the battery on the charger, it was indicating an 80% charge for nearly 24 hours worth of charging and never did reach full charge status.

so, does anyone have any ideas why a month or two old lightly used battery & charger would corrode or why my amp would freak out when i hooked a new pair of 8 ohm (easy load) speakers up without EVER turning volumes up loud? for what it's worth, it seems like the new right speaker isn't playing as loud as the left.
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Sounds like your battery is defective due to over-discharge.
Do you have a battery cut-out circuit to prevent over-discharge?
Is your charger correctly set up for that particular battery type/model (not all batteries are equal)?
I would say your battery charger is responsible for the noise. There's no way it's designed to handle the demands of an audio system -- especially those of a subwoofer.. Also, a Battery Tender will not charge a battery unless is has a certain level of charge; it simply will not work.
Build or buy a decent power supply, and maybe even throw in a good farad range audio cap.
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