Input caps picking rfi??

[slmnklyc]

Hi..
I am trying to build a stereo amp based on 2*ta8210 chips.
I check the noise while my ears is very close to the speakers)
And I have an hiss background noise that increases with volume pot movement..The noise exist even zero volume..Source is connected or not result is same..

So I tried a few things.
Nothing connected to amplifier inputs!!..
I also have 1nF bypass cap close&connected to the input pin of the chip and goes to gnd..
1-I shunt input rca + & -
Noise is fix(independent pot movement) and decreased..
2-I connect input cap shield(electrolitic cap) to gnd.
Noise is fix(independent pot movement) and decreased..
3-I connect positive side of input cap(leg goes to input pin of the chip) to gnd.
Zero noise..Dead quite..

Does this mean that input cap picking rfi??
I use cheap input cap..

How can I remove the noise completely?
If you have any experience similar to mine, can you share it with me?
Or do you have any guess/suggestion for me?

 

[rayma]

How can I remove the noise completely?

Can you post photos of the pcb and wiring?

 

[slmnklyc]

Can you post photos of the pcb and wiring?

 

[scottjoplin]

1-I shunt input rca + & -
Noise is fix(independent pot movement) and decreased..

It sounds like noise being picked up by the unshielded/untwisted input wires.

 

[slmnklyc]

^^ I forgot to add this:
I also shunt the negative of the input cap to gnd
Result is decreased and fix noise.

 

[sesebe]

Use shielded or at least twisted wire to make internal signal connections.
With the input unconnected it is normal to receive some noise.

Use shielded interconnect cable to connect the amplifier to a audio signal source.
You have the same noise?

 

[slmnklyc]

When I connected the negative(source signal coming side=leg goes to volume pot) of the input cap to gnd, noise decreases and fix.
When I connected the positive(leg goes to chip) to gnd, it is dead quite!!
So can we say input cap picking noise??

 

[scottjoplin]

Everything will be picking up noise to varying degrees, all the more so because it's not in a screened case. I doubt very much there is anything wrong with the capacitor. What you are describing is normal and to be expected under the circumstances.

 

[slmnklyc]

I also tried to put it inside metal case, results were same.

 

[scottjoplin]

Short out the input capacitor

 

[slmnklyc]

Short out the input capacitor

I tried it now and Dead quite!!
What does this mean??

 

[scottjoplin]

Can you post a picture showing what you've done?

 

[rayma]

I tried it now and Dead quite!!
What does this mean??

This looks like a single supply amplifier circuit, so the input blocking capacitor is necessary.
Does the amplifier still work when you short the input capacitor, which blocks DC and protects the source?

 

[slmnklyc]

Can you post a picture showing what you've done?

I connect +&- of the input cap.
Did you mean this?

 

[slmnklyc]

This looks like a single supply amplifier circuit, so the input blocking capacitor is necessary.
Does the amplifier still work when you short the input capacitor?

I didn't connect it to source when I shorted the +&- of the input cap.Probably it can damage to the speakers..

 

[rayma]

I didn't connect it to source when I shorted the +&- of the input cap.
Probably it can damage to the speakers.

That could also damage your signal source, as well as cause the amplifier to malfunction.
If the source has its own blocking capacitor maybe not, but it depends on the details.

The noise could be high frequency oscillation.

 

[phase]

Have you tried a ferrite on the input leads?
Sometimes those work to narrow down a source of rfi.

 

[slmnklyc]

Let's assume input cap picking noise..
What can I do for this?

 

[scottjoplin]

This looks like a single supply amplifier circuit

Ah, that probably explains why it's silent with the capacitor shorted

Remove the short and see if it still works

 

[slmnklyc]

Ah, that probably explains why it's silent with the capacitor shorted

Remove the short and see if it still works

Oh you think input caps are extra
Yeah it still works..