I need to fix a sub amp

[icor1031]

My sub woofer plate amplifier is (once again, I think it's indirectly caused by bad wiring in the home.) making my sub play a sound similar to sizzling bacon.

I was told it's likely caused by over heating.



What parts are likely bad?

Thanks.

 

[duke37]

What is a plate amplifier?

Give details of make, model and active devices with a circuit diagram if possible.

What bad wiring do you have/
What is overheating?

 

[solo2racr]

What is a plate amplifier?

A plate amp is one that mounts inside the subwoofer enclosure. Single channel amp, generally with a low pass crossover included and sometimes with a high pass out. Can be any class (A/B, D, etc.)

 

[icor1031]

What is a plate amplifier?

Give details of make, model and active devices with a circuit diagram if possible.

What bad wiring do you have/
What is overheating?

http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-803

I don't know what part inside the amp is overheating, I'm a noob and just repeating what some techs told me.

As far as wiring, I get a 60Hz tone when I connect more than 1 input.
I assume that can prevent it from using the auto-shut off (because it's still getting a signal), contributing to it's heat issue.

 

[KrisBlueNZ]

Can you give more information?

1. So the sound like sizzling bacon comes out of the subwoofer? Not from the plate amplifier itself?

2. Does it do this all the time while the amp is powered?

3. Does it sound like a clean hiss, or does it have crackles and pops? Can you describe it in more detail?

4. Does the sound vary in volume randomly? Does it change in volume if you adjust the gain control?

5. What effect do you hear if you change the power option between "always ON" and "ON only when a signal is detected"?

6. If you play a signal into it, do you hear that as well?

7. If so, does it sound clean and undistorted?

8. If so, can you play it at full volume and it still sounds OK?

9. Tell us everything you know about the history of the amp.

10. You say there's a hum when you connect more than one input... what are you using to provide the input signals?

11. Can you connect the sources in either order and the hum only appears when both are connected?

12. Are the signal sources powered from the AC mains?

13. Can you try feeding one input from an isolated device (e.g. the headphone output of a cellphone) when another input is connected?

14. Does the heatsink of the amplifier get warm when you play a low-level signal through it for ten minutes?

15. Are there any questions that I don't know to ask, where the answer could help us become more familiar with your setup, the history of the amplifier, the details of the problem, etc?

Please try to answer ALL of these questions. Any one of them may give us the important clue that helps us understand the problem.

 

[icor1031]

Can you give more information?

1. So the sound like sizzling bacon comes out of the subwoofer? Not from the plate amplifier itself?
Yes, I believe when I pressed the cone, it was damped. I can double check when it starts up again.

2. Does it do this all the time while the amp is powered?
Not yet. (see 15)

3. Does it sound like a clean hiss, or does it have crackles and pops? Can you describe it in more detail?
I think the latter, link here:

4. Does the sound vary in volume randomly? Does it change in volume if you adjust the gain control?
Yes in the first, and I don't know yet about the second.

5. What effect do you hear if you change the power option between "always ON" and "ON only when a signal is detected"?
No difference.

6. If you play a signal into it, do you hear that as well?
Yes.

7. If so, does it sound clean and undistorted?
Yes, except it's *adding* the sizzling bacon sound.

8. If so, can you play it at full volume and it still sounds OK?
I'm too scared to try full volume, I wouldn't want to fry my ears or go past xmax. But, when it starts sizzling again I can try increasing the volume.

9. Tell us everything you know about the history of the amp.
Listed at 15.

10. You say there's a hum when you connect more than one input... what are you using to provide the input signals?
RCA from two different receivers.

11. Can you connect the sources in either order and the hum only appears when both are connected?
Yes.

12. Are the signal sources powered from the AC mains?
My receiver is powered from the house's AC, and so is my amp - if that's what you mean.


13. Can you try feeding one input from an isolated device (e.g. the headphone output of a cellphone) when another input is connected?
I don't have an adapter cable to take 3.5mm to RCA.

14. Does the heatsink of the amplifier get warm when you play a low-level signal through it for ten minutes?
No.

15. Are there any questions that I don't know to ask, where the answer could help us become more familiar with your setup, the history of the amplifier, the details of the problem, etc?

This is my third one. They all work for a while, and this one for the longest - I used auto-on instead of always-on, and that reduced the heat.

On my previous amps of this model, I used always-on because I thought the auto-on wasn't working. It turns out, it just has a much longer delay than another model of amp I used previously

A tech told me that this issue is caused by heat.

I forget if I said this in my OP, but the sizzling issue comes after being on for a little while right now. With experience from my other amps, it will get to the point where it's always, or almost always present.

Also, often it doesn't ever turn off now when using the auto setting. I assume that's from the damage, as it worked before. And when I notice it a few hours later it's playing a louder tone (though not, or not always sizzling.) It seems to be a single tone.

Please try to answer ALL of these questions. Any one of them may give us the important clue that helps us understand the problem.

Thanks!

 

[KrisBlueNZ]

Sounds like the hum may be an earth loop. If both of your signal sources are earthed independently to the mains earth, when you plug them both in to the amp, a loop is formed, with a low resistance. For the rest see https://en.wikipedia.org/wiki/Ground_loop_(electricity)

I couldn't hear anything in your video, but you said that playing a signal makes the noise worse. In that case it COULD be a problem with the speaker driver itself; can you disconnect it and connect the amp to a different speaker? Just to eliminate the speaker itself.

Have you Googled for other reports of noise problems with this make and model of amp? If it's a common fault as you suggest, there should be plenty of discussion about it.

So there's a constant tone? Is this the sound that appears when you connect two receivers to it, or a different sound?

If you turn it off for five seconds then back on, so it doesn't have time to cool down, do the problems disappear and start reappearing after the same delay, or do the problems reappear immediately because the unit is still warm?

Can you make another video with clear audio that shows the three problems - that is, (a) the hum from connecting the two receivers to it, (b) the crackling that increases as you increase the volume of the signal, and (c) the tone that gets louder over time.

Can you post photos of both sides of the board? I want to know whether it has a DSP (digital signal processor) on it.

 

[solo2racr]

I had to turn up the audio in the video to hear the noise. I recognized it and it took me awhile to remember where. Then I remembered. I had a bad opamp in a guitar pedal that caused the same noise through the speaker.

Not sure if it relevant here though.

 

[icor1031]

Sounds like the hum may be an earth loop. If both of your signal sources are earthed independently to the mains earth, when you plug them both in to the amp, a loop is formed, with a low resistance. For the rest see https://en.wikipedia.org/wiki/Ground_loop_(electricity)

I'll be moving very soon. I know the wiring in this house is horrible.

I couldn't hear anything in your video, but you said that playing a signal makes the noise worse.

Only after time, and randomly. Seemingly when it heats up. And when I get a new amp, I don't have a problem at all for a long time.

Have you Googled for other reports of noise problems with this make and model of amp? If it's a common fault as you suggest, there should be plenty of discussion about it.
No luck. I hope the terms I used in my search were decent.

So there's a constant tone? Is this the sound that appears when you connect two receivers to it, or a different sound?
The hum as you mentioned first is a constant tone, and it happens when I connect two receivers to it. But I'm not too concerned about that, as it should go away when I move . My concern is the sizzling bacon sound. I believe that sound doesn't go away even if I disconnect all inputs.

If you turn it off for five seconds then back on, so it doesn't have time to cool down, do the problems disappear and start reappearing after the same delay, or do the problems reappear immediately because the unit is still warm?

The bacon sound remains. If there's a delay, it's a very short one. Unfortunately, it hates me - right now it doesn't want to start sizzling again for me to test it . It usually doesn't go away this long, lol.

Can you make another video with clear audio that shows the three problems - that is, (a) the hum from connecting the two receivers to it, (b) the crackling that increases as you increase the volume of the signal, and (c) the tone that gets louder over time.

I'm afraid I don't have the software to separate audio from video in order to boost it and make it clearer.

Can you post photos of both sides of the board? I want to know whether it has a DSP (digital signal processor) on it.

I will look. Right now I'm playing music trying to make it sizzle again.

Thanks.

 

[icor1031]

I had to turn up the audio in the video to hear the noise. I recognized it and it took me awhile to remember where. Then I remembered. I had a bad opamp in a guitar pedal that caused the same noise through the speaker.

Not sure if it relevant here though.

Thanks for helping!

 

[icor1031]

I'm sorry about the delay. Ironically, it still won't do that, which is very odd.