fix noise while adding a preamplifier

[sim_tcr]

My setup,
3 x PAM8610 for driving total 5 speakers
1 X TPA3116D2 for subwoofer
All of above amplifiers powered by SMPS with 12V.
When there is no source connected to the amplifiers' input I could hear small humming noise from speakers.
Once source is connected, everything works nicely (no noticeable humming or any distortion).

Now I am adding a preamplifier to the setup, I am hearing small humming noise from speakers.
I tried different RCA connectors/cables, even tried powering the whole setup with a 12V battery. Same issue.

Any thought about fixing it?

Note: I tried adding capacitor across amplifier input, that kind of reduce the noise. But it reduces the volume greatly.

 

[hifimaddy]

• Plug your amp and preamp to the same plug; maybe due to the grounding issues, humming will occur.
• If your preamp had a very low RCA output voltage, this is another issue.
• But try to look at your grounding; this will be the main issue, i guess.

 

[sim_tcr]

• Plug your amp and preamp to the same plug; maybe due to the grounding issues, humming will occur.
• If your preamp had a very low RCA output voltage, this is another issue.
• But try to look at your grounding; this will be the main issue, i guess.

All my setup is powered from same SMPS 12V which is connected to the wall socket via 3 pin plug.
I tried connecting to different wall socket already.
If I am using 3 pin, that means I am doing grounding, correct?

 

[mbhangui]

Note: I tried adding capacitor across amplifier input, that kind of reduce the noise. But it reduces the volume greatly.

Gosh, you are a brave person . You are shorting the input and almost the entire signal goes down the drain charging and discharging the capacitor. Don't try this adventure on a speaker output.

The only place you place a capacitor destructively like this is across a DC power supply to short the DC ripple.

If you want no hum with no source connected, connect a 10k or 20 k resistor across the input instead of a capacitor

 

[mbhangui]

My setup,
3 x PAM8610 for driving total 5 speakers
1 X TPA3116D2 for subwoofer
All of above amplifiers powered by SMPS with 12V.
When there is no source connected to the amplifiers' input I could hear small humming noise from speakers.
Once source is connected, everything works nicely (no noticeable humming or any distortion).

Now I am adding a preamplifier to the setup, I am hearing small humming noise from speakers.
I tried different RCA connectors/cables, even tried powering the whole setup with a 12V battery. Same issue.

Without any source connected or load connected on the input, the inputs become extremely high impedance (in few megaohms) source and any metal wires, copper traces connected to the inputs act as antenna and catch the 50 Hz ac signal flowing through your house wires.

Check if you get a hum with some source connected to the amp or preamp input. Even connecting a volume pot across the input will eliminate the hum as it will make the impedance equal to the DC resistance of the volume put.

 

[sim_tcr]

Gosh, you are a brave person . You are shorting the input and almost the entire signal goes down the drain charging and discharging the capacitor. Don't try this adventure on a speaker output.

If you want no hum with no source connected, connect a 10k or 20 k resistor across the input instead of a capacitor

Thank you for correcting me, I am still a noob in electronics, I read in internet that, capacitor is the way to filter noise.
Please correct me if I am wring, you are suggesting to wire a 10K to 20K resistor across the preamplifier input/s (as I have 6) or in amplifier input/s (as I have 6) as below?

Check if you get a hum with some source connected to the amp or preamp input. Even connecting a volume pot across the input will eliminate the hum as it will make the impedance equal to the DC resistance of the volume put.

I tested already that without preamplifier in setup, source (DAC out) connected to amplifier I have no issue with hum.
When preamplifier is added, I get hum.

Below is my full setup,

 

[Yelamanchili manohar]

My setup,
3 x PAM8610 for driving total 5 speakers
1 X TPA3116D2 for subwoofer
All of above amplifiers powered by SMPS with 12V.
When there is no source connected to the amplifiers' input I could hear small humming noise from speakers.
Once source is connected, everything works nicely (no noticeable humming or any distortion).

Now I am adding a preamplifier to the setup, I am hearing small humming noise from speakers.
I tried different RCA connectors/cables, even tried powering the whole setup with a 12V battery. Same issue.

Any thought about fixing it?

Note: I tried adding capacitor across amplifier input, that kind of reduce the noise. But it reduces the volume greatly.

Hi Sim

Please try plugging all the open RCA sockets which are acting as antenna's with the below plugs and see. All the best

 

[mbhangui]

What you have done below is connected the resistor in series or in-between. Across means you have to connect it in parallel.

But from what you showed is everything is connected. In which case you don't require to put the 10k resistors. If you are getting hum with everything connected you have to find out the source of the hum.

e.g. disconnected the 5.1 dac and connect 10k resistors across all the inputs of the pream. If the noise still comes, it means that the 5.1 dac is fine.

What is this 5.1 amp. Is it a board or a proper commercial AVR?
If it is a kit, disconnect the output of the preamp to the 5.1 amp and connect the 10 k across all the inputs of the amp and then check if the hum is still there. if it is there it means your amp is the culprit. If not, it means that the hum is coming from the preamp output.

Thank you for correcting me, I am still a noob in electronics, I read in internet that, capacitor is the way to filter noise.
Please correct me if I am wring, you are suggesting to wire a 10K to 20K resistor across the preamplifier input/s (as I have 6) or in amplifier input/s (as I have 6) as below?

View attachment 86577

 

[sim_tcr]

What you have done below is connected the resistor in series or in-between. Across means you have to connect it in parallel.

But from what you showed is everything is connected. In which case you don't require to put the 10k resistors. If you are getting hum with everything connected you have to find out the source of the hum.

e.g. disconnected the 5.1 dac and connect 10k resistors across all the inputs of the pream. If the noise still comes, it means that the 5.1 dac is fine.

What is this 5.1 amp. Is it a board or a proper commercial AVR?
If it is a kit, disconnect the output of the preamp to the 5.1 amp and connect the 10 k across all the inputs of the amp and then check if the hum is still there. if it is there it means your amp is the culprit. If not, it means that the hum is coming from the preamp output.

Is it below how resistor connected across/parallel? Also is it ok if I use 22K resistor instead of 10K for this test?




5.1 amp is a DIY with a combination of 3 x PAM8610 and TPA3116D2

I am pretty sure with source connected (that is what I believe you are asking me to connect 10K resistor across the input to simulate load) to amplifier, I have no humming problem.
It is when preamplifier added to the circuit, problem arises.

I will anyway try as you suggested to find out exactly.

 

[mbhangui]

Is it below how resistor connected across/parallel? Also is it ok if I use 22K resistor instead of 10K for this test?

That is ok.

5.1 amp is a DIY with a combination of 3 x PAM8610 and TPA3116D2

I am pretty sure with source connected (that is what I believe you are asking me to connect 10K resistor across the input to simulate load) to amplifier, I have no humming problem.

across the preamp input. This will cause 0 v across on the preamp input without the DAC connected to the preamp. 0v means the output of the preamp also should be 0 v unless the preamp is generating some noise internally.

It is when preamplifier added to the circuit, problem arises.

I will anyway try as you suggested to find out exactly.