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LM3886 - Noisy signal unless inputs shorted

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scottjoplin

scottjoplin

Banned
Joined 2015
The layout is standard, that is looking from the front the left and right pins are the ends of the track and for a volume pot, left would be signal ground, right would be input, the middle is the wiper and would go to the amplifier along with the ground. The distances are not standard.
 
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Hogwild

Member
Joined 2010
PSU board and components are stock, as sold by Chipamp.com (CarlosFM snubberized).

Amp Boards are stock Chipamp.com LM3886, except for the following resistor changes to reduce gain:
Rf=20K
R2=20K
R3=1K

Everything else stock. No additional components (I'll add protection stuff when I have this sorted out).




Keruskerfuerst said:
Can you give some more information?
PSU, board, values at LM3886,.....
Click to expand...
 
scottjoplin

scottjoplin

Banned
Joined 2015
They are both good quality pots from respected manufacturers, I doubt you'd hear any noise from either, but you pays your money and you takes your choice ;)

Pots like those with pins are easier PCB mounted, some are available with tabs with a hole for wiring to directly but I've wired directly to PCB mounting pots, it's a bit fiddly though.
 
H

Hogwild

Member
Joined 2010
Just a warning for anyone thinking of buying PE stuff and getting it shipped to Canada.

Hmm...there appeared to be a bit of a catch. Parts Express wanted $USD 24.50 to ship two volume controls to Canada. What a ripoff. In the end, I ordered them anyways, and PE only charged $USD 16.50, but let's face it, they probably could've charged $8.00 or less if they'd only put it in an envelope.
 
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Hogwild

Member
Joined 2010
Wait...I'm not clear...you wrote
"then ground it to amp ground with a piece of wire.."

What is it I'm grounding to amp ground with a piece of wire?
The POT?

Thanks



JMFahey said:
Don´t overthink it, you are not testing that amp the way you will actually use it.

Just connect a speaker at its output, a sound source (PC/MP3 player/Smartphone/CD player) to a volume pot, between 10k and 50k, Audio/Log taper preferred, and from it to the amp, using a coaxial cable.
Also coaxial cable and properly soldered connectors between sound source and potentiometer (a real one, with metallic case soldered to ground)
Also place the amplifier board inside a metallic case or at least on a piece of wood, to which you glue a piece of kitchen type aluminum paper, then ground it to amp ground with a piece of wire, and place an insulator (cardboard or a magazione will do) on aluminum so it does not short PCB bottom.
Play some music and *then* worry or not about Hum and external noise.
Click to expand...
 
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Hogwild

Member
Joined 2010
scottjoplin:

As I said earlier, I really don't wish to use coax. I tried two different kinds. Noise levels got worse when I used them. Plus, it's extremely difficult to get coax in there. The space is so tight it's ridiculous. I'll never again work on a project this small. It's great if you're 19 and have x-ray vision and the hands of a surgeon.
 
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