Headphone port sound now quiet at full volume
The internal speakers work fine and volume is normal, but all of a sudden I now have a problem with sound when using the headphone port. I always have had the mac hooked up to an amp and speakers, to watch films etc, but now even at full volume I can hardly hear anything. I have plugged in headphones (thinking it may be the amp/speakers and experience exactly the same. I have also plugged my iphone inot the amp/speakers and it works fine, so problem Any ideas?! Is this a software or hardware problem?
iMac (21.5-inch, Late 2012), OS X Mavericks (10.9.2)