< Picture: output pcb replaces stock DCX2496 output board
Design details
To keep the interchannel crosstalk at a premium, each channel has it's own input- and output ground connections (called references) brought out of the chip. These need to be connected to a low impedance ground (plane).
The power supply voltages are a bit odd, around +/- 9VDC. The reason that it's not the expected +/-5VDC is because that would not give enough output level for pro use. With +/-9V, output can be as high as 5VRMS with vanishingly low distortion. The recommended supply connection takes the feed to a total of 8 pins, with decoupling between the voltages. I followed this recommendation in my prototype. The power comes from the DCX2496 +/-15V analog supplies, followed by a 3-pin 7809 & 7909 regulator. My unit is absolutely silent.
The digital ladder switches operate from 3.3VDC. Again, digital power comes from the DCX (+5V digital in this case) followed by a 7803.3 regulator. The same 3.3V also supplies the micro-controller.
This is all static stuff so once you have done your setting of the levels, there is no more digital activity in the chip and no digital noise.
The block diagram
The overall block diagram is shown below. There are two analog signal paths: one is from each of the three balanced output DACs (AK4393) to a balanced-to-single ended converter to the level control chip. From the level control chip, the signal goes to the output XLR connectors. So, there are 6 outputs, for stereo 3-way crossover. Just like a standard DCX. The other analog path is from the analog RCA inputs A and B to the level chip, and from there to single-ended to balanced converters and then on to the DCX internal A/D converters (AK5393). So, you can use this unit with analog inputs as well as digital inputs. You can also use this unit with unbalanced (RCA) power amp inputs unchanged.
Then there is the control stuff. There is a micro-controller in the system, which is just a little chip that looks like a normal opamp with a couple of additional pins (2*7 instead of 2*4).
The block diagram seems huge, but there's only two small PCB's to stuff. The output board can be seen in the above picture. NOTE: The pic is from the first prototype with RCA outputs; the final version has XLR outputs for either balanced or unbalanced operation.
[Construction Guide] [Spec sheet]
[User Guide] [XXL Stuffing Guide]
![[XXL Stuffing Guide]](images/DCX%20XXL%20stuffing%20guide.bmp){kind=link}
The board that holds the IR receiver, microcontroller and display is even smaller and fits just on the front panel. The important thing is that I program this chip do do the following:
- receiving the codes from the IR receiver when you press a button on the remote;
- depending on the button you pressed, send commands to the level chip to change the attenuator settings to increase or decrease the level in a channel as commanded;
- send commands to the display to show the levels as they are set.
Of course, we need a power supply for the whole thing, and this is derived from the existing DCX power, again just using the existing flat cable connectors on the DSP board. There is no change to the DCX supply unit.
