Liquid Crimson --> Liquid Platinum II
If you haven't seen this, please go here:
https://www.head-fi.org/threads/mon...-by-alex-cavalli.876406/page-28#post-14575341
To squeeze a balanced Crimson into the Platinum sized box at 1/4 the price requires several engineering changes.
1.
Power output - Today's headphones are, in general, more efficient than when the Crimson was designed. While back then 4-5W might have been a necessity, today it is not. Most (but not all) headphones will run happily to ear-splitting levels at much less power. Thus, the first engineering change is to reduce the power output. Not by than much, but by enough to be practical. This includes going to a balanced topology which reduces the rail voltages considerably.
2.
Power supplies - there simply isn't enough room for a big transformer and linear supplies in the box and on the board. The only possible solution is an outboard supply, in this case for efficiency an SMPS. Then, this SMPS is used to create all of the needed supplies - LV rails, Housekeeping, HV and Heater.
The HV and Heater supplies are made with small DC-DC converters. These are efficient, small, and perfectly suitable for the constant low current requirements of the tube portion of the circuit. Some would claim that linear supplies would be better here even if they provided less voltage. I would disagree. The Platinum HV supply makes over 100V to place the 6922 at a very good operating point. The CTH, to note, also has a 100V HV supply instead of a lower voltage linear one.
Thus, the very big Crimson linear supplies are replaced with very small and/or outboard supplies which are all super efficient. This reduces the power demands of the amp a lot and the power dissipated by the non-audio components.
3.
Power Dissipation - the confines of the new box and lack of external heatsinks demands much lower power dissipation. This is partly accomplished with the new supplies. It is also accomplished by reducing the idle currents in the output devices significantly. Whereas the Crimson's output devices burnt almost 5W each at idle the Platinum's output devices burn less than 1/2 per device. The Platinum's outputs are cooled through the board making it possible to get it all in this small enclosure.
4.
SMD vs Through Hole - the Crimson was nearly entirely hand-assembled through hole components (expensive). The biggest change in the footprint of the Platinum is its use of SMD components. They are vastly smaller, don't compromise the performance, and are auto assembled dramatically reducing the manufacturing cost.
All of these 4 engineering changes working together are what makes it possible to offer the Platinum in its small box at the current price point.