is my amp fried?

[useless idiot]

I purchased an amplifier last week on eBay & it has an issue. I bought it as-is/untested, so I can't just get my money back. I'm hoping someone here can help explain to me what is wrong with it & how it can be fixed. I paid $170 for this amp, so I'm hoping it's repairable.

There is a very faint high pitch noise that can be heard inside the amplifier. It is not an external ground, RCA, or headunit issue. I hooked the amp power/remote/ground directly to the battery & it makes this noise. I then hooked the speaker outputs of channel 1 & 2 to a pair of sealed subs. One of the subs began producing a noise. And this is without the radio on or the RCA's plugged into the amp. I plugged the RCA's in & turned the stereo on & the subs both began playing normal. After I turned the stereo off the right sub was still producing the same noise. It's not a humming sound like you here with a ground issue/alternator whine, it was more like a constant 45hz tone.

It began getting dark & cold outside so I was unable to test channels 3 & 4. I believe the noise is

coming from the RCA inputs for channels 1 & 2, at least that's the area you hear it from.

I'm pretty mechanically inclined & have basic knowledge of electronics, so I'm hoping this is something I can fix myself.

The amplifier is a JL Audio 450/4 v1. Any & all help is greatly appreciated! Thanks.

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[useless idiot]

Anybody?

 

[MakeItVibrate]

Amps shouldnt "hum" unless the have an internal fan. Which that amp does not. Looks like you might have just got ripped off. If you bought it on a credit card you may be able to file a complaint with them and get your money back.

 

[audiobaun 5,000+ posts]

Ya that may be a reason for the e-bay sell.I always test my stuff before i put it up for auction/ sell.I cant believe people just rip you these days for a quick buck??There are a couple guys on here that repair amps, and might be able to tell you exactly what is needed to repair it.Kinda sound like a bad ground issue/ or even a bad RCA connection on the board, but Who knows without breaking it open???File the complaint before the due date through pay pal though.

 

[useless idiot]

Amps shouldnt "hum" unless the have an internal fan. Which that amp does not. Looks like you might have just got ripped off. If you bought it on a credit card you may be able to file a complaint with them and get your money back.

It's not really a hum, just a high pitched sound. You can't even here it unless you stick your head right next to the amp.

Ya that may be a reason for the e-bay sell.I always test my stuff before i put it up for auction/ sell.I cant believe people just rip you these days for a quick buck??There are a couple guys on here that repair amps, and might be able to tell you exactly what is needed to repair it.Kinda sound like a bad ground issue/ or even a bad RCA connection on the board, but Who knows without breaking it open???File the complaint before the due date through pay pal though.

It was sold as-is with no guarantee it was working. Once the stereo is on it plays fine. Actually, I played it a good 45 minutes & the amp didn't even get warm. I'm really convinced it's something very simple such as a broken leg/solder joint on the RCA input.

 

[audiobaun 5,000+ posts]

Ya .. Id break it open and check the board out

 

[useless idiot]

Ya .. Id break it open and check the board out

I'm just trying to get some info on what to check beforehand. Slash amplifiers are a pain to disassemble.

 

[audiobaun 5,000+ posts]

I hear ya..I have a couple laying around that I havent finished up myself(amps). I use an old sub magnent to hold all the screws in one spot so i dont loose them .. been lucky so far.Hope you get it fixed man.//content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[useless idiot]

Nobody?

 

[akheathen Premium Member]

it's likely a bad cap in the rail side, and/or shorted transformer. i'm sure that ringing is transformer noise and can be effected by physicaly tapping on the amp, or pushing on the transformer/board, and changes in power. a little physical manipulation usually fixes the problem. do not power it up without the transistors clampped to a heatsink. other than messing with the transformers, and checking for bad transistors or dry/loose connections, it would be best to send the amp out to someone experienced in repairing them, so they have the scope, scematic, and intuitive knowledge of the components. jl amps can be pretty complicated to work on, in comparison to most other amps, and you do not want to damage the drivers

 

[useless idiot]

it's likely a bad cap in the rail side, and/or shorted transformer. i'm sure that ringing is transformer noise and can be effected by physicaly tapping on the amp, or pushing on the transformer/board, and changes in power. a little physical manipulation usually fixes the problem. do not power it up without the transistors clampped to a heatsink. other than messing with the transformers, and checking for bad transistors or dry/loose connections, it would be best to send the amp out to someone experienced in repairing them, so they have the scope, scematic, and intuitive knowledge of the components. jl amps can be pretty complicated to work on, in comparison to most other amps, and you do not want to damage the drivers

After taking it apart it has a couple of blown transistors on the heat sink. It does cut in & out when you tap on it.

 

[akheathen Premium Member]

well, you are going to want to replace the whole section of transistors, and the corresponding resistors. then, trace the circuit to the little driver for those transistors and check that for short between the legs. i don't know if it uses individual drivers, or ic's. that may fix it if there is no further damage, plus manipulating the transformer slightly to see if the noise stops.

 

[useless idiot]

well, you are going to want to replace the whole section of transistors, and the corresponding resistors. then, trace the circuit to the little driver for those transistors and check that for short between the legs. i don't know if it uses individual drivers, or ic's. that may fix it if there is no further damage, plus manipulating the transformer slightly to see if the noise stops.

My dad has a friend who's an electronics technician. I'm gonna see if he'll fix it for me. I was just trying to find out if this was a small problem or more damage then the amp is worth to fix.

 

[SPLluminator 10+ year member]

Sounds like what happened when my leads came off the speaker and they touched. My 250/1 V.1 made that same noise and the low ohm light came on indicating the problem. Check to make sure you dont have a short in the speaker lead as well.

 

[useless idiot]

Sounds like what happened when my leads came off the speaker and they touched. My 250/1 V.1 made that same noise and the low ohm light came on indicating the problem. Check to make sure you dont have a short in the speaker lead as well.

How would I go about doing that? I have a cheap dmm somewhere.