Dev AMP in other words means development amplifier. It is the project which i nowhere seen even close to be similar to this. It is really unique. It is not because i wanted unique, but because i needed proper way to evaluating how amplifiers with different output impedances sound. Super short background:
Usually all amplifiers are voltage drive. Vin -> Vout. It is old school approach. Easy and simple.
Next step current drive amplifiers which are with very high output impedance Vin -> I out. Voltage in - current out. Many people would tell this is very complicated to build, but in reality it is easy.
Next step is mixed mode amplifiers where at low frequencies they are voltage drive and at high frequencies they are current drive. These are a little more complicated, but not that hard.
Next step is negative output impedance at resonant frequency and high impedance at high frequencies. And probably any other configuration where different output impedances start and stop according to frequency. This becomes quite difficult if frequencies need to be adjusted.
Next step do all that like adjusting frequencies for output impedances and possibility to switch between modes on the go by the one touch on my phone. Voltage, current drive, mixed mode with negative impedance or without. Any configuration. Plus all that should support different drivers from sub to tweeter to fullranges. Plus stability margins should be safe. And output impedances variation pretty high. This is a very hard task. Plus considering circuit minimalistic as possible and cheap as possible. Plus noise floor to go under 20dbA uVrms. Which translates to to around >120dBA dynamic range amp with on board DAC.
So really it is a challenging task. Good thing that simulations are done and it should work i hope. Now there are two possible circuits simulated to achieve that. I am going to build this amp in order to compare the sound. I tried to compare sound of negative output impedance amp and current drive amp. They provide very interesting differences when equalised to identical response. So different that Dev AMP need to be made in order to test and explore all possible output impedance configurations on the go. Sure all types equalised to the same response. In theory negative output impedance at resonance and high impedance at high frequencies should be best. But who knows, need to test in practise before to go with more simple amp solution if that exist for all possible drivers. Dev AMP is not ment to be technology for products, just to decide what technology to build.
Pic.1 Phase margin of Dev APM with one of working modes
Pic.2 Example output impedance with one of working modes