…there's Jason Stoddard with the complete Weldenheim chronicles. It's a lengthy post on Head-Fi.org that maps the Jotunheim R gestation story. Extrapolating, "the story starts back in the Sumo days now almost three decades past. We made power amplifiers that could deliver 200A per channel on a short term basis. We used an error correction scheme that allowed us to turn up output current to 11. Refer to Hawksford and Cordell if you want the theory behind it. The first Jotunheim prototypes included the Hawksford/Cordell/Sumo error correction scheme. I pulled it out of the final design at least in part because it could deliver enough current to weld the TRS jack to the plug if you got it into your head to yank the headphones out at the wrong time when playing loudly…
Very first Jotunheim hack
"I made it a point to go to LA CanJam and stop by the Raal/Requisite booth where Danny was with our Vidar loaner and a few other amps that sell for much more. He clearly liked ours and happily told people how good it was. I still hadn't heard his headphones. I'd heard so many in my career that I thought I had a pretty good grasp on the breadth and depth of how they could sound. But this was completely unlike anything I'd ever heard before and completely different from what I expected. Even on the loud-ass show floor, the Raal/Requisite were the most dynamic, transparent headphones I'd ever heard. Furthermore, they didn't sound anemic or thin from being an open-baffle design. They had bass. Maybe not a ton of sub bass but it sounded shockingly realistic. Eventually I took them off. 'We need a pair of these.' That's what started it all."
Weldenheim stage 3
Jason next explains how Danny subsequently visited Schiit to look for a complete SR1a system and happily settled on a DAC/pre combo with one or two Vidar. Jason simply thought that particularly for recording engineers, these plus Raal's impedance adapter were still more boxes than ideal. Enter the direct-drive notion. He remembered that Sumo amps used to do 50-200A into 0.1Ω on a burst basis. He knew that Danny said the SR1a needed 7 amps of current into 0.2Ω before clipping. He opened his mouth and said he thought he could do it.
Jotunheim R prototype board
For exactly how Jason slew his impulsive dragon, read the full post. It explains how R-rated Jotunheim is a completely different beast than PG13 Jotunheim. There's a different transformer and overrated 15A output devices. There are smaller emitter resistors and far lower internal resistance. There's a more complex 4-layer PCB and Nexus output stage with Zobel filter to avoid oscillation. There's active baffle step compensation (not Raal's passive approach with resistors and inductors). There are Hall effect current sensors with thermostat to enforce 'mute' should the deck try to source more than 31 amperes from both channels or exceed 95°C. Finally Jason explains what he got out of this project.
"OG tech is a direct result of Jotunheim R's development and already a working proof-of-concept prototype. With more refinement, it could end up being foundational tech for entirely new classes of products. But that's only one piece of new technology. While developing Jotunheim R, I was so excited by the possibilities that I came up with other new ideas. I still have to prove some of them but they are things we'll be working on this year. So while the Jotunheim R project may have seemed like a distraction, it led to entirely new vistas. Sometimes you have to get weird, chase the bizarre and have some fun because you don't know where it might go." That's not trickle down but up and sideways, way sideways. Blame Aleksander Radisavljevic and Danny McKinney for what their SR1a made Schiit do.