I am guessing that there is an incompatibility with the 3.5mm jack and some earbuds.
I presume you have a lead that goes from a male 1/4" jack to a female 3.5mm socket? And you are plugging your earbuds into the 3.5mm female socket?
Some earbuds have volume controls or microphones, and these use a modified 3.5mm jack. A normal stereo jack has a tip contact and two ring contacts along the pin separated by insulating rings. Jacks with built-in volume controls or mics have a tip contact and three contact rings along the pin.
What might be happening is that the normal stereo 3.5mm socket on your lead is shorting out one or more of the rings on the earbud plug. Your are only hearing anything via the signal "finding" an alternative path through the impedance of the mic or volume control or other circuitry.
If I am right, you will need to solder a four contact 3.5mm female socket onto your adapter lead, and connect to the audio connections, leaving the fourth control connection unconnected.
Alternatively, it could be an impedance problem. This is the 'resistance' of the headphones, as seen by the amplifier. If you plug in phones/ buds of too low an impedance, the audio amplifiers feeding the socket might not be able to supply enough current to operate the buds - hence your very low sound level. See if you can look up what the impedance of your buds is, anything at or above 600 Ohms should be OK. Anything lower than that might be your problem.
I don't have the Ohms symbol on my keypad, but it looks a bit like a horseshoe with the open end at the bottom.
Last edited by Uplinker; 8th Feb 2021 at 11:47.