Strange GC noise problem

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pacoblackxx

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Joined 2010
Hi, i build my first lm3886 amplifier. Everything is ok but..i have a strange problem.

The wire from potensiometer's out that goes to the chip board line-in is very sensitive to noise(for both channels). When i touch them( or moving my hand above them) the speakers make noise.

I had them twisted at first, but a had a noise problem. Then a removed the twisting and the problem gone for a while but today it started again..

My case is wooden and only the top surface is aluminium. When i remove the aluminium the noise is very little, but a can hear it late at night. when i mount the top aluminium surface the noise gets a little more audible, even if no wire is touching it.. I noticed that if i connect pot's in with pot's out (as like no pot is there) the noise almost dessapears...its very hard to hear it even if you are too close to the speakers(2-3cm).

Any recommendations?
 
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pacoblackxx

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Joined 2010
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mjf

Member
Joined 2009
hello.
do you have a central ground point (star ground) ?
have you connected the alu cover to this point?
has your pot a metal case which is not connected to ground?
........and you can use shielded wire from pot-out to chipamp input.
greetings
 
Sangram

Sangram

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Joined 2002
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I've had chipamps in open air without case and never experienced noise problems.

The pot is always wired with signal to pin 1, amp's input to pin 2, and ground to pin 3. This way the input starts off short-circuit (no signal) and goes to full output (full signal) as the pot rotates clockwise. The way you've done it, the amp input starts off by seeing an open resistance and the line-in starts by seeing a short-circuit.

With the shaft facing you, the left most is pin 1 and right most is pin 3. Pin 2 is the wiper.
 
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pacoblackxx

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Joined 2010
sangram said:
I've had chipamps in open air without case and never experienced noise problems.

The pot is always wired with signal to pin 1, amp's input to pin 2, and ground to pin 3. This way the input starts off short-circuit (no signal) and goes to full output (full signal) as the pot rotates clockwise. The way you've done it, the amp input starts off by seeing an open resistance and the line-in starts by seeing a short-circuit.

With the shaft facing you, the left most is pin 1 and right most is pin 3. Pin 2 is the wiper.
Click to expand...


hmmm i changed the wires as you told me and there is no sensitivity anymore!oh yeah baby.:D A will wait until night where my room will be very silent, so i can hear if there is any noise.

But the sensitivity is gone for sure! thnx mate
 
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epitaxial

Member
Joined 2010
Chip volume

Also, wire lengths should be short and neat, and if a ground plane board is used, the wires (bundled) should be tightly run along the surface of the board. In some cases it should not touch the board, but it is easy to find the correct way (less noise).

You could use fixed resistors in the NFB network for volume too.
 
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