(Amp Guts) Help with noise **PICS**

[amedeuce 10+ year member]

This is the inside of my JBL px300.4. I have narrowed down the noise in my system (HISS) to the amplifier itself by

1) Using muting plugs

2) Removeing the amp from the vehicle and using a "test bench" if you will and a test speaker to find the same noise.

It's a low hiss with the vehicle OFF and ear right up close to speakers.

By "test bench" I mean I connected the amp right by my battery with the ground going straight to the battery and used a test speaker and adjusted every setting on the amp with no change - gains at zero - no rca's connected.

So I took off the cover not the entire sink case and looked around. Here are the two things odd I found. I'm no expert and if this won't cause noise, I'll just have to live with some minor hiss till I get it repaired or get a new amp.

Click to read more...

 

[amedeuce 10+ year member]

Or maybe someone has some ideas of what to look for inside the amp to help me out.

Or maybe, well it has to be the amp only thing that is the same from the test is the vehicle battery.

I used different wires, speakers, grounded to the battery, different turn on lead, different head unit.

Maybe it's the h/u wire harness? Some wire in there?

 

[amedeuce 10+ year member]

Currently Active Users Viewing This Thread: 4 (3 members and 1 guests)

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[amedeuce 10+ year member]

Oh well, no help from the master squeak9798.

Could this still be a ground loop noise, even though I've grounded the amp to the battery? Other grounds in the vehicle causing the hiss?

Or should I face it, it's the amp.

 

[amedeuce 10+ year member]

Anyone? Hello?

 

[req 5,000+ posts]

dunno man. tried it in somone elses car?

or on a 120v powersupply?

 

[amedeuce 10+ year member]

dunno man. tried it in somone elses car?
or on a 120v powersupply?

I was gonna try that but the wife left in her car.

But I figured if I could elimiate everything else except the battery and the head unit.

I did find out after I reinstalled the amp that the noise (HISS) does increase with the gain, but with the gain at minimum there is still noise

I should say when I set my gain with my oscope the hiss does not increase, only when gain is moved to 3/4 to full does the noise increase.

But from let's say about 1/2 or 5/8 gain to zero gain the noise is the same level.

The Hiss ONLY goes away when I set the filter(s) to low pass on the amp.

The Hiss is there in high pass and in flat

 

[oldschool4me 10+ year member]

not sure about amps but a common similar issure that i have found with computers is when you hear that start looking for caps going bad. swollen, leaking, etc.

 

[amedeuce 10+ year member]

UPDATE!!!

Here is the response to the email I sent to JBL about the hiss

I spoke with our engineers regarding this. The hiss that you

hear is actually considered normal for this amplifier model.