See here more details:

PIANO 2.1 DAC:

PIANO HI-FI DAC (VERSION 2.1)
We are using 2 DAC ics PCM5142 with integrated DSP. The PurePath
software from TI is available for download (registration required) and can
be used to create specific filters and other audio functions.
The board will come pre-programed as a 2.1 output (but you can create your
own custom design and load it the board and can access the xover
frequency directly from linux (we made a small app).
Hardware wise, we have split the digital and analog side with LDOs and we
feed the analog side using an extremely capable (low noise ultrahigh psrr)
LT3042. Basically each board has 4 LDO (2 for each DAC ic) (note that
digital side uses cheaper LDOs).
Of course, on the analog side we used only thin film resistors and poly caps
in audiopath.
Key Features
Dedicated Two no’s of 384 kHz/32bit high-quality DAC PCM5142 for best sound
quality
Available with different output connectors: 4 x RCA
DAC SNR is 112dB
DAC THD+N @ - 1dBFS are –93dB
Full Scale Output of DAC is 2.1Vrms
Dynamic Range of DAC is 112dB
Sampling Frequency ranges from 8 kHz to 384 kHz
Ultra-low-noise voltage regulators for optimal audio performance
Integrated EEPROM for automatic configuration (with write-protection)
Technical Specifications
Operating Temperature Range is -25C to 85C
The Piano 2.1 board size: LWH = 68.7mm* 65 mm*22.2mm


VOLT + AMP :

VOLT+ AMP
The TPA3116/18 class D amplifier IC is a leap in terms of audio quality.
Our board is a high quality implementation of the stock design.
Ÿ Using TPA3118 (better grounding of main IC)
Ÿ Anti-Pop circuit
Ÿ Bootstrap snubber mod
Ÿ Brand name components as per picture
Ÿ Radio avoidance switch (to reduce interference)
Ÿ PCB with extra copper (since on transient’s current can spike to 5A)
Note that PCB comes in 2 flavors:
1. Volt is a shield and beneath it has connector that will plug into our DACs
(Piano 1.1 and Piano 2.1). It has no RCA inputs. (Capacitance Multiplier can
be added as a standalone board).
2. Volt+ is a standalone amplifier with RCA IN (stereo). In addition to
everything that the Volt has, we have added a circuit in the power supply
that will reject spikes and noise to about 60db. The name of the circuit is
"Capacitance Multiplier". Please note that Class D amplifier needs a quiet
PSU.
Volt+ can be used with our DACs through the RCA input, as a standalone
board.rrect crystal (there are 2), fixing the problems outlined in the
beginning.

Key Features
This class D amplifier goes up to 2 x 50W max
The components used are specifically designed for high end audio devices (Worth
Inductor, TI chipset, film capacitors and ± 1% thin film resistors)
VOLT AMP boasts 4 output filters, 4 EMI Snubbers, 4 bootstrap capacitors and
gain setting components
We are using CM filter circuits in power section to reduce maximum ripples in
power
We are using 10K logarithmic Potentiometer for Volume control. Available with
different Input connectors: 2 x RCA
Comes in two flavors
Technical Specifications
Chipset: TPA3118D2
Output: 2 x 30W into a 4 to 8-Ω BTL Load
Class D Operation: 90% POWER EFFICIENCY
SNR: 102dB
Supply Voltage: UP TO 24V DC
Board Size: LWH = 82.83mm* 125.5mm * 40.2mm
Temp Range: -40°C to 85°C Ambient

KALI reclocker:

Kali The Goddess of Time
Every SBC has a crystal that it used to send digital signals to your DACs.
The accuracy of this crystal is very important in how well the DAC will
transform the digital signal into analog sounds. Simply put: a better crystal
means a better sound! Most SBCs use a very cheap crystal with lots of jitter
in order to save costs.
Furthermore, there are 2 kinds of frequencies for digital files: 44.1Khz (wave
files) and 48khz (streamed music). Some SBCs (like RPIs) can output only
48Khz, so imagine the degradation of the sound that was recorded at a
different frequency.
Kali Will Solve Both of Those Problems
First, it has a very low jitter NDK crystal feed by LDOs in series for ultra quiet
power supply. Second, the FPGA will read the incoming stream, will buffer
the DATA 0.7s while discarding the incoming clocks. Using the NDKs it will
reclock the buffered data OUTSIDE the fpga (since fpgas introduce about
200ps of jitter) and provide a MCLK/BCLK that is direct from crystal,
providing a jitter-free (almost) to your DAC.
Meanwhile, it will clock the file using the correct crystal (there are 2), fixing
the problems outlined in the beginning.
The Million Dollar Question (actually $69):
How Does it Sound?
Well, the music will "open up". The stage will sound bigger, more tridimensional.
You will hear sounds, words, instruments that were drowned
before in a sea of digital mud.
Is it Worth it?
Do you enjoy a better wine/microbrewery beer, or anything will do? Do you
have some medium/good speakers or you are using the cheapest PC
speakers? Do you love music or just want to hear some beats?
We can’t answer the question for you. It’s your choice.
Kali Comes in 2 Flavors
The difference between the two is that RPI version will always buffer the
DATA at 0.7s. It will work with any SBC's including SPARKY.
Key Features
The basic design includes FPGA based FIFO board, Clock generation board and
additional board for connecting other types of inputs like SPDIF and USB along
with I2S streams of audio
I2S input: 44.1 KHz, 48 KHz, 88.2 KHz, 96 KHz, 176.4 KHz, 192 KHz - 16bit, 24bit or
32bit
I2S output: 44.1 KHz, 48 KHz, 88.2 KHz, 96 KHz, 176.4 KHz, 192 KHz - 16bit, 24bit
or 32bit
FIFO Memory: 4MB SRAM
Can be use with external Crystal Oscillators for MCLK or upgraded to a higher
quality, multi-frequency clock that comes with automatic Fs switching and better
performance
LED indicators (Power, Full, Lock, Empty, Sample Rate, Mclk)
DC power supply: (5V/3A) with Filter circuits
Multi-frequency output capability to support the full I2S working range from 44.1
KHz to 196 K
Automatically switching frequencies according to the input I2S signals
Extremely fast and very low propagation delay Flip-Flops are added on I2s signals
output from FPGA, for synchronization with MCLK before sending to DAC
Ultra-low-noise voltage regulators for optimal audio performance
Integrated EEPROM for automatic configuration (with write-protection)
Tech Specs
LED indicators (Power, Full, Lock, Empty, Sample Rate, Mclk)
DC power supply: (5V/3A) with Filter circuits
Operating Temperature Range is -25C to 85C
The Kali board size: LWH = 58mm * 77.54mm * 23.8mm

CM board:

Capacitance Multiplier (Stand Alone)
A Capacitance Multiplier is designed to make a small capacitor function like
a capacitor that is much, much larger.
This design reduces the output ripple/noise of any PSU to almost negligible
levels (less than 5mV up to 1Mhz).
Note this this is not a voltage regulator. The output voltage will track the
input voltage (- dropout voltage).
This circuit is very suitable for class A and class D amplifiers or even to feed
clean power to your SBCs.

Key Features
Designed to make a small capacitor function like a capacitor that is much, much
larger
Reduces the output ripple/noise of any PSU to almost negligible levels (less than
5mV up to 1Mhz)
The output voltage will track the input voltage (- dropout voltage)
Suitable for class A and class D amplifiers
Suitable to feed clean power to your SBCs
Dropout voltage is trim pot selectable