The Digital Controlled Speaker System "DiCoSS" started with the Inrush Current Control (ICC) unit that performs the following functions controlled by a MSP430F2011 microcontroller.

- Switch the auxilliary and power amplifier Torroid transformers sequentially at the mains zero crossings, taking relais latency into consideration.
- Control the Torroids inrush currents.
- Monitor the audio input to switch on the system and switch the system off upon a system error or after a time out period when no audio is present.
- Monitor a push button to manually switch the system on and off

The second project was the design of the power amplifiers, six in total to drive the left and right channel bass- and mid speakers and tweeters.
All speakers are directly connected to their respective amplifiers.
The power amplifier design is flexible in that you can choose for a 2+2 parallel output stage to drive a 3 Ohm minimum speaker and a single output stage to drive 8 Ohm speakers.
The bass speaker power amplifier can deliver 250 Watts at 4Ohms up to 330 Watts at 3Ohms reactive, supplied from a dual 56V supply.
The mid and high power amplifiers can deliver 100 Watts at 8Ohms from a dual 48V supply.
The power amplifiers are power limit protected in that the current limit kicks in at lower levels when the voltage over the power transistors is higher.
This prevents the power transistors to operate outside their Safe Operating Area.
The output of the amplifiers is switched by a special audio power relay (Amplimo) that is activated by the Inrush Current Controller (ICC) unit.
A DC detection circuit on the power amplifier PCB monitors the presence of a DC voltage on the power amplifiers output, switches off the relay and signals the error condition to the Amplifier Fan Controller (AFC) unit, that in its turn signals to the ICC unit to turn off power.
The design had to be compact to fit into a slim line loudspeaker enclosure.
The Amplifier PCB is 10x8CM with the power transistors mounted directly under the PCB on a heatsink.
The power amplifier for the bass speaker has its own heatsink, the mid and high power amplifiers share a single heatsink.
At high power levels the heatsinks need some form of airflow to stay at a moderate temperature.

That lead to the third project, the Amplifier Fan Controller (AFC) that controls the speed of two fans in series dependent on the heatsink temperature.
Small 14mm x26mm PCB's with a temp sensor were mounted, one on the heatsink for the bass power amp and two on the heatsink for the mid and high poweramps.
Their outputs are taken in by a MSP430F2012 micro controller on the AFC board to determine heatsink temperature and control the fan rotation speed.
The MSP430 also takes in the power amplifiers DC level detection and signals to the ICC if an emergency powerdown is required.
This can be either a DC level on one of the poweramps or a heatsink reaching a critical temperature in which case the power amplifier  torroids are switched off but the auxilliary powersupply remains active to allow the fans to cool the heatsinks down to an acceptable level.
Once this low temperature is reached the auxilliare powersupply is switched off as well and the system goes into standby mode, waiting for an active audio input signal.

The PAAS (Power Amp Auxilliary Supply) generates the dual voltage of +/-12V for the power amplifiers output relais drive circuits, the ADDA signal chain board that contains the audio converters plus a 5.5V output for the lower (logic) voltages in the system.

One passive PCB, the Power Amp Power Supply (PAPS) was designed to connect the Power Amplifier bridge rectifier and 10.000uF bulkcaps and provide connectors that can carry the high currents involved in such Power Amplifier designs.
One PAPS supplies the low Power Amp and another PAPS provides power to the mid and high Power Amps.

The ADDA audio I/O board was by far the most complex project.
Over 300 components are placed on a PCB area of 10x8cm to fit the area above the heatsink next to the bass power amplifier.
Input signal filtering, phase splitter and biasing to drive the ADC, an I2S link into the TAS3208 audio DSP board and two I2S links back from the TAS3208 audio DSP board into two DAC's with their I-V converters, differential to single conversion and output filters.
Clocking for the TAS3208 that operates in slave mode driven by a low jitter TENTLABS oscillator and circuitry to derive the back EMF signal from the bass speaker and feed it back into the bass power amplifier.
There is also a connector added for a piggy back PCB to support an optical digital audio input.

I decided to use the TAS3208_LC Evaluation module.The advantage of that EVM (Evaluation Module) is that it comes with a USB connection and a Graphical User Interface that allows you to create filters and all sorts of basic DSP functions by a mouse click.

Once you have the system running you can change parameters on the fly which made the tuning of the frequency curve quite easy. The DSP program is loaded in on board EEPROM and starts execution when powered up even when the USB cable is not connected.
The USB connector is also used to power the TAS3208 EVM
One disadvantage of the software (Pure Path Studio) is that the GUI only works under Windows XP, there is no support for Win7,8 or higher.

The last step was the input board that takes in the audio signal, the USB interface, the (optional) optical audio input and the manual On/OFF pushbutton.
The PCB was split in half where the other half located a small circuit to take in the clip signals from the ADC and the three power amplifiers driving the CLIP LED on the front of the loudspeaker.
There are in total four LEDs on the front of the loudspeaker, one LED indicating the system is either in sleep or active, driven from the ICC unit. Two LEDs from the AFC unit, a DC error LED and a TEMP LED, indicating a critical heatsink temperature and the fourth LED indicates a clipping condition. This LED takes the OR function of the ADC clip signal on the ADDA unit and the three clip signals from the low, mid and high Power Amplifiers. 

You can also find pictures of the electronics shassis metal work and the woodwork of the loudspeaker enclosures which were fun projects to do as well.