80s hair primarily. I listened to a ton of 50, 50+ and 100+ clips last night and loved them all. Best I can gather is it adds bass response and he says it's a factory installed mod rather than someone having it installed by a 3rd party.
This X1000. I had an HR 100 with the XL mod; called Soldano and Bill Sundt walked my tech through removing it within a week. Supposed to add low end but was mud city even with a boost. Much better after removal
The only Soldano I ever owned was a Hot Rod 50 with the XL mod. I didn't know much back then but I do know that I couldn't get it to sound good. Way too much low end and mud that couldn't be dialed out.
Is the mod just a fixed deep cap, a variable one, or something else? Our 50 Plus has a front panel depth control that is a nice addition, although only required sometimes.