alto ts312 low output Muffled sound

My Alto, TS312, virtually identical to my Headrush 12, has a low, muffled output, which it did not have previously. How can I troubleshoot the problem? What is the likely cause? It used to sound Identical to the Headrush.

crwdns2934089:0crwdne2934089:0 crwdns2934093:0crwdne2934093:0

crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 0
crwdns2934285:0crwdne2934285:0