Ember 2.0 board rev:
1: Supercharger now built in so tubes with heaters >500mA can be used. To use >500mA in Ember (and Horizon) the 'supercharger' had to be installed.
2: The way the input capacitor bypass is done is different. The functionality is the same but when you remove the jumper in Ember-II the sound cuts out where in the Ember 1 this doesn't happen.
3: When a headphone is inserted the line-outs are disconnected in Ember-II, in Ember I the line-outs are always 'on'.
This functionality in Ember-II can be changed to Ember-I alike behaviour by adding solder drops on specified spots BUT when a headphone is plugged in that has a varying impedance AND the output R is set to 'M' or 'H' the tonal balance is altered by the (impedance of that) headphone.
4: An 'anti-volpot-scratch' modification is implemented which counters the 'scratchy sound' you hear when the input capacitors are bypassed and sometimes even (faintly) with input cap in line.
Of course this has a disadvantage too and with some specific tubes
Tubes that run under starved plate conditions (the ones intended to be run on plate voltages of 200V etc.) and/or have high grid current leakage may cause a noise current over the used resistor and this may become audible on sensitive headphones.
5: The Ember-II has an attenuation module which can easily be changed to get another amount of attenuation (if needed)
The Ember-I has an attenuation jumper but you can only choose between no attenuation and a fixed amount of attenuation where in Ember-II you can alter the attenuation by plugging in another module.
6: In Ember-I there was a circuit that switched off the output relay when the output stage over heated (added in the design stage).
Because in reality the output stage never even got warm this functionality is left out (was pointless) in Ember-II.
7: For sort-off the same reason (protecting the output stage) a resistor that was added in the design stage of Ember-I has been removed in Ember-II.
This results in slightly measurable (but not audibly) more output power in Ember-II for low impedance headphones only.
8: 2 power supply capacitors are used in Ember-II where 4 were used in Ember-I. The total capacitance remained the same though.
9: The extra 'power LED' that was present on Ember-I is left out in Ember-II.
10: The opamp used for heater voltage detecting is now SMD sized, in Ember-I it was DIP-8 sized and mounted in a socket.
11: Ember-II is using different heatsinks (smaller ones) because they were severe overkill.
These are all minor changes that do not affect the sound quality aspects.
Sound and measurement wise the Ember-I and Ember-II are the same.
Ember-I can be 'converted' to Ember-II functionality with a few changes to the boards + addition of the Supercharger.
This involves cutting traces, running some extra wires on the bottom and adding resistors, removing attenuation resistors and soldering 'sockets' in its place etc.
The only reasons why one may want to 'convert' an Ember-I to Ember-II functionality (or want to upgrade to Ember-II) are:
Wanting to use >500mA heater tubes.
Or are bothered by the scratchy pot (ONLY during volumne adjustment, NOT when stationary)
Or when you want the RCA out to disconnect when a headphone is inserted (when doubling as a pre-amp for instance).
Soundwise they are completely tube dependent and with Supercharger or Ember-II you simply have more tube choices (those with higher heater currents).
