I'm new here but am pretty sure I'm supposed to say this here:
Some time ago I bought an amp and speakers from an old man who didn't hear well anymore, but I didn't come here to talk about that.
The fact is that with this purchase he gave me as a present an old pair of SR-40 (with its SRD-4) because those didn't worked well anymore, the right side was clearly quieter than the left one and if I tried to balance the volume (through my amp) to equalize both sides the right side's quality went off and everything sounded fried, so I quickly gave up, connecting back my speakers to the amp. At this time I had my speakers connected to the SRD-4 for a while and don't remember of anything not working correctly aside from the headphones (but my memory's sometime terrible).
This was more than a year ago now, and recently decided to give these headphones another shot, so I connected the SRD-4 to my amp (the same one) and my speakers, this time the right side did not emit any sound, and when turned on loudspeaker mode my right speaker do not do anything as well. So in the end I've got headphones with only the left side producing music (and with a pretty good quality at that) when the SRD-4 is turned on earspeaker mode and only my right speaker working when the SRD-4 is on loudspeaker mode.
I apologize if this post does not belong here, thank you for reading this and I hope to get answers from you.