TPA3116 - need some help

[Igla]

Hi;

I just got this amp from eBay.
TPA3116 Digital Amplifier Board Dual Channel 30Wx2 With Treble Bass Tone | eBay
I ordered this version because it's cheap and it has tone controls - I need them for the project for my father.
First thing is when I touch potentiometers the amp makes some noise. I suppose I need to wire the housing of all potentiometers to ground? Where should those wires go from the housing? To signal ground to the input or somewhere else?
Second thing is this amp has no output chokes (filter). I can't hear there is anything wrong when listening to music because of that but I wonder if it's OK to run the amp without output filters.

I would appreciate some help.

Regards;

 

[FauxFrench]

It is possible to use without an output filter BUT it will radiate a lot of electromagnetic noise that may disturb radio reception. My suggestion is to add an output filter.
The rods of the potentiometers are metallic. They may have electrical contact to the sliders inside. If so, you you cannot just ground the rods. Better, get 3 plastic knobs for the rods.

 

[Douglas Blake]

I would not suggest running without the output filters. Depending on your speakers, you might end up with damaged tweeters.

Maybe try this board instead ... https://www.amazon.com/dp/B07XZC6YJV ... it's only a couple of bucks more.

(They say 150 watts ... it's more like 50 watts per channel on 4 ohms, 35 on 8, with a 24 volt supply)

 

[Igla]

Thanks for the answer FauxFrench.
Well; if there is no harm to loudspeakers without output filters I won't loose sleep.
My father won't mind radio reception disturbances when listening to music from CD player.

About potentiometers;
Yes; I have plastic knobs (came with the amp) on the rods of potentiometers. The amp makes the noise when I touch knobs. Strange.

 

[FauxFrench]

The idea without an output filter is that the speaker wires add some inductance (filtering) and the speaker drivers anyway are too slow to react to the carrier frequency. If you have expensive dome or band tweeters, I would not use them with this amplifier without an output filter.
If you put the plastic knobs on the potentiometers, you have hum when you actually touch the plastic knobs and not with your fingers close to the knobs (not touching)?

 

[Igla]

No; just some old 4'' full range speakers. I got them from old computer loudspeakers. I will make a sound bar for my father.

Do you have any theory about pots? Why the amp makes some noise when I touch the knobs?

 

[FauxFrench]

If you put the plastic knobs on the potentiometers, you have hum when you actually touch the plastic knobs and not with your fingers close to the knobs (not touching)?

 

[Igla]

Yes; only when I touch the plastic knobs the amp makes some noise or hum.
Otherwise the amp is quiet.

 

[29285]

This looks like an indication these pots are of high impedance - presumably 100kOhm. just for that reason I prefer 10kOhm pots at this position. Normally there is no risk connecting the metal case of the with GND, or minus supply.

 

[FauxFrench]

Can you try to touch the negative supply terminal to the amplifier to see if you get the same noise/hum?

 

[FauxFrench]

Found a potentiometer of this type in my stock. It seems that the axis is not electrically connected to the mid-pins. You can ground the axis and voltwide is (once more) right.

 

[Igla]

Thanks for the help.
I will try as soon I get home. I'm stil at work now.
I will also check with multimeter if metal parts of housings of the pots are connected to ground.
Otherwise I would need to desolder the pots to measure the value. I couldn't find anything written on the housing of the pots.

 

[Igla]

'' Found a potentiometer of this type in my stock. It seems that the axis is not electrically connected to the mid-pins. You can ground the axis and voltwide is (once more) right. ''

Thanks. I will play with the amp when I get home and post the results.

 

[Igla]

I forgot to ask...
The housing of the pots - do I connect them to signal or to power ground?

 

[29285]

I forgot to ask...
The housing of the pots - do I connect them to signal or to power ground?

Providedl the case has been isolated this should make no difference at all.

 

[Igla]

Well; I did ground the housings of potentiometers and the thing got worse. I got more hum.

‘’ Can you try to touch the negative supply terminal to the amplifier to see if you get the same noise/hum? ‘’
If I touch negative supply the amp gets dead quiet.
Does that mean it has a ground problem somewhere in the circuit?

 

[Turbowatch2]

If you can, shoot a picture how you grounded the pots. Usually this should work. You may, amp and power off and discharged, measure the resistance of the pots metallic part to ground. Should not show any value.

The output filter problem could be minimized by running the output lead 2-3 turns through two ferrite rings, near the board.

 

[Douglas Blake]

Well; I did ground the housings of potentiometers and the thing got worse. I got more hum.

What are you using for your power supply?

 

[Igla]

'' If you can, shoot a picture how you grounded the pots. ''
Each pot with a short wire – from housing to ground pins of the pot. Perhaps I should solder those wires to the same point – like PS negative pin?

'' What are you using for your power supply? ''
I'm using 19V 5A laptop power supply which seems to work OK with my other TPA amps.

 

[Turbowatch2]

Ground the metal part of the pots at the power ground. You can connect the pots with one wire in a row and then go to power - negative = ground. Many of these pots hum, they get silent when screwed to a metal case that is grounded. Otherwise you have to use such a wire.