Better capacitors may help but the possible bigger issue is the proximity to the power transformer.

If you use the speakers in this opened state and the humming is gone with the board out like that but getting worse with the board nearing the transformer you have a difficult situation without a good fix...

Had the same issue a couple of weeks ago. My issue was the 3.5mm cable I used that was too thin and picked up interference from power cables.

But there can be other issues as well. For example a ground loop. There are some (US specific?) power line filters that can mitigate this. Also try to connect the computer and speakers to the same power outlet.

There are also 3.5mm (car) audio filters which could help (for example: https://www.amazon.nl/dp/B06XQYN77L?ref=ppx_y … _fed_asin_title).

Hi, those four diodes might be a bridge rectifier.
If they're aged/worn, they might cause some slight humming passing through.
It's just an idea, though. It can be something else as well.

I recapped the board and replaced diodes. It actually wasn't the diodes causing the hum since I tested after replacing them and got no improvement.
What did help was the recap. Now the hum is lower, but still there. I guess I'll have to live with it - after all it's never going to be audible over the sound of an AT power supply fan!!
The hum doesn't change with proximity to the transformer. I guess if it did you could hack a barrel jack onto the speaker and use a 12v wall wart power supply instead.

I fixed 50hz hum on my Logitech S200 speakers according to http://www.jpf.de/jpf/logitech_s200_humming/page_01.htm , by moving and rotating the transformer. The hum is so quiet now you would have to come really close to hear it.

One reason why I avoid 2.0 speakers is very little space to move the transformer. There is a lot more space in subwoofer.

I have 2.1 Genius speakers that also have quite audible hum and a broken amplifier (it degraded over 15 years) resulting in very poor and low quality amplification and left/right unbalanced volume. I will probably get an oscilloscope with spectrum analyzer function for that as it will be easier to fix the hum.

Hi, asked my dad for advice.
He thinks that the humming can be reduced by applying a little bit of nail finish (old aceton solvable type that dryes up) to the transformer's metal sheets.
At the side of the transformer, where often the metal frame is located that holds it together.
He says the vibrations between the loose metal sheets are the culprit.

Jo22 wrote on 2025-04-20, 13:08:

Hi, asked my dad for advice. He thinks that the humming can be reduced by applying a little bit of nail finish (old aceton solva […]
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Hi, asked my dad for advice.
He thinks that the humming can be reduced by applying a little bit of nail finish (old aceton solvable type that dryes up) to the transformer's metal sheets.
At the side of the transformer, where often the metal frame is located that holds it together.
He says the vibrations between the loose metal sheets are the culprit.

This is the reason why I saw "varnished" copper threads?
Interesting.

Transformer laminations being loose can produce physical noise that won't be heard from the speaker cones themselves. You can listen if the transformer actually humms or even buzzes, which can also happen if a 220V transformer is ran at 230 or even 240V because the core experiences higher magnetizing currents. On better things there's often an extra winding for 240V and it is best to make use of it in order to reduce physical noise the transformer makes, but the cost is slightly lower output voltages which often plays in your favor as it means the linear regulators also get less hot.

Double the capacitor value, or scab on a small coil/inductor after the first capacitor followed by another capacitor. That should significantly help with PS hum. Or ditch the transformer entirely and use a more modern external electronic PS "brick" to supply it.

After that I'd switch to better shielded input wire.

I wouldn't blame transformer laminations unless it is the transformer itself producing audible hum

Yeah, it is usually not the transformer itself that makes the noise. Extra capacitance can definitely help a lot, and a good modern brick will fix the issue for sure.