The DÆ v3.0 Battery Charger/Power Supply is used to power DÆ subsystems including various combinations of stepped attenuator, phono preamp, differential input board and filter/output board. Power for the analog subsystems comes from a 36 volt battery pack made up of six, 6-volt valve regulated lead acid batteries. The battery pack can power the analog electronics for more than six hours. If the battery is depleted after a really really long listening session, the charger automatically kicks-in to recharge the battery and power the audio electronics. While charging, the noise level of the analog electronics is typically a little bit noisier than under battery power. Often the difference between battery mode and recharge mode is difficult to measure.
The schematic for the DÆ v3.0 Battery Charger/Power Supply is available here.
DÆ v3.0 Battery Charger/Power Supply Top
The DÆ v3.0 Battery Charger/Power Supply has many improvements over the previous versions.
Here is a list of the key features:
The +/-17 volt supply rails that power the analog electronics is provided from a virtual ground. The alternative is to divide the 36 volt battery pack into two 18 volt sections. The advantage of the virtual ground is that the battery capacity is better utilized allowing a longer run time;
A microcontroller is used to control the Battery Charger/Power Supply. The cold start and switching between battery mode and recharge mode is managed by the microcontroller. The microcontroller also implements many safety precautions like avoiding trying to charge a completely dead battery;
The switching of the battery charger, battery pack, battery voltage measurement and battery voltage balancing is implemented using solid state relays to avoid the clicking noise of electomechanical relays used in previous versions;
All power is provided by a single 48 volt desktop AC/DC adapter. Previous versions required two adapters; one for 48 volt and another for 12 volts;
A hot-swap/soft start circuit is used on the 48 volt input plug to avoid the spark that would result from charging the large 1000 uF filter capacitor that is part of the battery charger circuit;
All connections to the battery pack are opened when the 48 volt power is removed. This minimizes the battery pack discharge rate during extended periods of non-use. Previous versions had a manual disconnect switch that the owner needed to remember to use;
The battery pack has a voltage balancing circuit to balance the charge on the six 6-volt batteries to maximize the battery pack capacity and listening time;
An linear optoisolator is used to isolate the battery pack from the digital measurement/monitoring circuitry. This results in very low noise on the power supply rails for the analog electronics.
I have also recently completed the design and construction of a triple differential input board and a filter/output board. These will be the subjects for future blog posts.
