A modular approach for hifi audio projects powered by the new Teensy 3.6
The CORE module is the central part of the project, so it has to be as functional as possible in order to mantain a wide range of use-cases spectrum even when used as a standalone module.
This will be achieved by using high quality and versatile components.
The CORE will be designed with a bias towards the Teensy 3.6, but retrocompatibility with the smaller Teensy 3.2 is an option. One of the downsides of using the Teensy 3.2 in this context is the lack of multiple SPI ports. MATT will have at least 4 devices on SPI busses, including but not limited to:
Plus, a lot of the SPI0 hardware CS pins, which are mandatory for the use with at least the display and the IOAPEX module, are taken by other functionalities (like I2S pins).
The Teensy might need to be permanently attached to the CORE module since some backside pins may be used (such as the D+/D- line for the USB connector), but a breakout of the Teensy pins will be available, as well as a USB type B plug for power and data transfer. The use of the USB EHCI in the Teensy 3.6 is an option, maybe in the form of a second USB type B plug, or maybe leaving bare PTHs on the board.
The USB 5V supply will power a 5 V to 5 V dc-dc converter for a clean, stable, reliable 5 V supply. This clean 5V will then power a SMPS that generates a +15 V rail and a -15 V rail. These rails will be used to supply all analog-only circuitry (such as ADC input filters, DAC output filters, ADC buffers and DAC buffers, etc.) in the CORE module. Using these supplies on the IOAPEX module may be an option. Also, an option for a +48 Phantom power supply is considered. Finally, battery powered operation may also be an option.
The CODEC on the CORE module will be an AK4621EF, with differential inputs, differential outputs, support for up to 192 KHz @ 24 bit resolution, and very high SNR and THD ratings. It needs to be connected via SPI to the Teensy for its control interface. You can check its datasheet for further details.
Using a powerful dual supply allows the design of a flexible analog section, which sports 4 Neutrik combo XLR+TRS connectors and optional amplification modules connectors. Every channel will have a balanced/unbalanced switch, a XLR/TRS switch, and a onboard/addon module selector.
The on board ADC filter and buffer accepts balanced signals up to 40 Vpp / 14.14 Vrms and unbalanced signals up to 20 Vpp / 7.07 Vrms, it then scales the signals down to its full scale input of 5.658 Vpp / 2 Vrms.
The on board DAC filter and buffer outputs a full scale balanced 5.658 Vpp / 2 Vrms signal, it then scales it to balanced 40 Vpp / 14.14 Vrms or unbalanced 20 Vpp / 7.07 Vrms. The CODEC serial interface allows for a digital output attenuator with 256+16 levels, for attenuation range from 0dB to -72 dB to mute.
The presence of a dual supply on the addon amplifcation modules connectors allows users and designers to implement custom preamp or final modules tailored to their needs. Sub-modules including but not limited to mic preamps, guitar or bass preamps, phono preamps, headphones amplifiers, speaker amplifiers could be easily implemented. Also, the presence of an high voltage supply on the POWER module will enable users to design more demanding solutions, such as loudspeaker or tube preamps.
In the next logs we will discuss the specs of the POWER and IOAPEX modules.
We will also discuss the sub-modules that will contribute to specific functionalities of MATT, such as analog submodules for the CORE, io modules for the IOAPEX, etc.