I finished HW implementation and testing for the precise & tiny DAC+HPA based on ES9038Q2M+AD8397 fully differential current mode bridge, USB-C input, 2.5mm jack 4 wires outputs, over 300mW@32ohm, 24/192, 46x20mm PCB. The DAC IC offers some THD manipulation options and I wish to let users choose 3 modes: a) normal mode with instant PLL locking THD@1kHz@-3dbfs .0005% THD@1kHz@-10dbfs .0003%(measured on the real HFM HE400i load), S/N looks close to -126dbA but to be sure I need to arrange AP 555 and remeasure b) performance mode with excellent THD@1kHz@-3dbfs .0003% THD@1kHz@-10dbfs .00017%, however PLL not fast enough to lock data without loses at starting(up to half of second at the begin of the track is muted) c) SE emulation mode, the same as normal mode but 2nd harmonic domination at level .01% I think or any value up to .5% or so So far I want to use follow scenario to switch between modes but I opened for any opinions and ideas regarding that: 1) Device powered On, MCU started and send initialization dump to the ES9038 for the mode determined variable MODE, which is = 0 that corresponds to the normal mode 2) during the first 0..1000mS the MCU flashing by "Power" LED 4 times, if power will be interrupted that period, next power-up the MCU will start with MODE = 1 i.e. performance mode 3) during next 1000..2000mS the MCU flashing by "Power" LED 8 times, and if power will be interrupted that period, next power-up the MCU will start with MODE = 2 i.e. SE mode 4) if during first 4S power wasn't Off the device operating in normal mode, and generally looks like USB DAC+HPA with 4S blinking LED after turning it On. I understand that such an interface is kinda weird but I want to let try users all features available with no extra complexity with buttons. Any high-res players like Neutron, has a volume knob, so I believe dongle like DAC doesn't need any buttons at all. Any opinion?