My 215c was the same. Thin, Sterile, Cold and Digital...sounded bad. Fitted a Celestion G12T-75 which are in the 1960 cabs. Slight improvement only. Was about to trade it, but first before giving up on it, I opened it up, checked the biasing and found it was set way too low at only 29mv per side. So I Put new JJ EL34 power tubes in and changed V5 for a Westinghouse ECC83 balanced tube. Left the original pre amp tubes in ( they are decent). Rebiased the new power tubes to 35mv per side and wow, big difference...night and day. This amp has now gone from being an amp I hated to the one I love. The clean sound is full and warm almost fender like. I have a fender deluxe reverb too and the JVMs clean tone is now right up there too since I made the changes. Tempted to try back the stock speaker again but the Celestion G12T-75 sounds great. Glad I tried this. Don’t give up on your JVM, they really are incredible amps. My little 215c will take on anything now and staying as my main gigging amp. Just why they send them out sounding like crap and underbiased beats me. This is why people often claim they prefer the sound of the Vietnamese made DSL40s better than what they see as thin sounding JVMs. The DSLs come biased correctly from Vietnam. If you’d sold your JVM because you didn’t like the thin sound that’s a real shame as it’s such an easy cheap fix...you could try to get another one and make the changes yourself if you know what to do and are comfortable working on it. If not pay a tech for half an hours labour to do this for you.