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Old 22nd April 2016, 06:59 PM   #1
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Default Hmmmmm Noise in One speaker

I have got 2.1 lm3886 amplifier. But one of the speakers is giving continuous hmmmmmm sound. When I directly connect input to amp there is no noise. Any idea how to remove this!
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Old 23rd April 2016, 08:03 AM   #2
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Generally, that noise happens when input load (input dampening) has failed/omitted.

P.S.
Also check for DC offset (excessive DC at the speaker jack).
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Old 23rd April 2016, 08:09 AM   #3
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Default Setup

This is my set up
input from rca to tone and tone to amp.
then from amp to speaker protection ans then output.

Click the image to open in full size.
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Old 23rd April 2016, 08:12 AM   #4
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Please check my set up if u can figure out.
1. RCA to TOne
2. tone to Amp
3. THen Speaker protection to output.

Click the image to open in full size.
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Old 23rd April 2016, 08:28 AM   #5
AndrewT is offline AndrewT  Scotland
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please attach your pics.
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Old 23rd April 2016, 03:07 PM   #6
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I have already attached image. please open it in a new window
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Old 23rd April 2016, 03:50 PM   #7
farley is offline farley  United States
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You've attached links to images stored on another server, somewhere. Inevitably the links will break, the hosting service will shutdown, or some other calamity will occur that will make the images disappear, removing context from the thread.

If you attach the pics directly to your post, as AndrewT requests, then the images will stay with the thread for as long as diyaudio is around.
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Old 23rd April 2016, 04:00 PM   #8
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Please check the image attached.
Attached Images
File Type: jpg IMAG0198.jpg (852.6 KB, 50 views)
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Old 23rd April 2016, 09:19 PM   #9
farley is offline farley  United States
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Are the input RCA jacks isolated from the chassis? It's difficult to tell from the pic.

There is a PCB assy that is floating in the air. Are there leads/circuits on the bottom of that PCB that are maybe touching conductive parts of the board underneath it?

The input signal leads cross over the toroid and a couple of EI transformers. I can't tell if the EI transformers are active or not but it may help to route those input signal leads away from the transformers.
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Old 24th April 2016, 03:18 AM   #10
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Yes, RCA are not isolated from chassis. I think no board is floating in air. It's placed on spacers. EI xformers are active. I think EI xformer will affect both amps not one. And noise is from one amp only. If I remove ground point on input of the amp with no noise then noise gets transferred from noisy to one whose ground I remove at amp input.
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