These boards are my newer projects, designed and assembled in 2016 or after. I consider these “better designs” and also more comprehensive test and measurement results are provided.


H-DAC – High performance 192 kHz / 24-bit DAC with addon options

  • Very high performance; measurement results with S/PDIF input:
    • Output level: 2.0 Vrms
    • Dynamic range / SNR: 122 dB (A-weighted)
    • THD+N ratio: -103 dB (0 dBFS/1 kHz signal, 48 kHz sample rate)
    • Crosstalk: -128 dB at 1 kHz, -112 dB at 10 kHz
  • Supports S/PDIF, Toslink, USB, and external I2S inputs
  • Unbalanced outputs (RCA) on board, balanced (XLR) addon available
  • Hardware-controlled – no need for microcontroller
  • Can be powered by AC or DC supply
  • Addon available to transform H-DAC into preamplifier/headphone amp
  • New output stage addons can be easily designed to experiment with components and circuits
  • CS8416 S/PDIF-receiver, PCM1794A DAC, LM4562 opamps (or any with the same pinout), LM2940/LM2990, TPS73633, TPS79133, and REG103 regulators

H-DAC is a hardware-controlled high-performance 192 kHz / 24-bit capable DAC board with TI PCM1794A DAC. The board has two coaxial S/PDIF, two Toslink, and one I2S input that can be either on-board 48 kHz / 16-bit USB receiver or an external I2S-device. Input selection and settings are controlled with jumper links that can be replaced by mechanical switches or microcontroller addon board.


Addon BalOut – Balanced output addon for H-DAC

  • Very high performance; does not become bottleneck of H-DAC system
    • Noise level: -117 dBV (A-weighted)
    • THD+N ratio at 2 Vrms output signal: better than 109 dB
    • Crosstalk at 10 kHz: 113 dB
  • Balanced output buffer with low-pass filter
  • Optional high-CMRR balanced drivers
  • Takes power and audio signals directly from H-DAC
  • 5×4 cm 4-layer PCB, LM49724 opamps (or any with the same pinout), optional THAT1606 balanced drivers

Addon BalOut is a small addon board to be stacked on H-DAC to add balanced XLR outputs. It works along with the unbalanced RCA outputs on H-DAC and audio performance is high enough not to be the limiting factor of the H-DAC system.


Addon H-PreAmp – Preamplifier/headphone amplifier addon for H-DAC

  • Very high performance preamplifier; measurement results with H-DAC and 2 Vrms output:
    • Dynamic range / SNR: 116 dB (A-weighted)
    • THD+N ratio: -102 dB (2.0 Vrms / 1 kHz, 48 kHz sample rate)
    • Crosstalk at 10 kHz: -113 dB
  • Very high performance headphone amplifier
    • Dynamic range / SNR: 115 dB (A-weighted)
    • Maximum output power / THD+N ratio:
      • 22 mW / -98 dB into 560 ohms
      • 230 mW / -85 dB into 33 ohms
      • More gain can be added for higher output power
  • Software controlled (Arduino compatible)
  • Balanced outputs (XLR) on-board and unbalanced connectors (RCA) on H-DAC board
  • Takes supplies and audio signals directly from H-DAC via pinheaders
  • 10×10 cm 4-layer PCB shaped to fit tall components on H-DAC board; PGA4311 volume control, LM49724 and LM4562 opamps (or any with the same pinouts), TPA6120A2 headphone amplifier, optional THAT1606 balanced drivers

H-PreAmp is an addon board for H-DAC, transforming the fixed-output DAC into a very high quality preamplifier with integrated headphone amplifier. H-DAC and H-PreAmp together provide single-ended (RCA) and balanced (XLR) outputs as well as headphone amplifier.


Addon H-Filter – Simple through-hole balanced preamplifier addon for H-DAC

  • High performance; H-DAC + H-Filter system performance measured with fixed resistors:
    • SNR: 119 dB (A-weighted)
    • THD+N ratio (1 kHz / 2 Vrms): -100 dB
    • Crosstalk: -112 dB at 1 kHz, -100 dB at 10 kHz
  • I/V-stage, filters, output stage, and opamps implemented with through-hole components for easy experimentations
  • Balanced outputs (XLR) on-board, uses unbalanced connectors (RCA) on H-DAC board
  • Potentiometer for volume control to transform H-DAC into preamplifier, or resistors for fixed output level
  • Takes voltage supplies and audio signals directly from H-DAC via pinheaders
  • 5×10 cm 2-layer PCB, through hole resistors and capacitors, placeholders for DIP8 sockets for opamps

Addon H-Filter is a simple filter and output addon for H-DAC with a possibility for a potentiometer to transform it H-DAC into a preamplifier. In contrast with other designs of mine, it has been designed with through-hole components to allow easy experimentations with opamps and passive components. It offers high performance with low BOM cost and easy solderability.


Addon H-MCU – Microcontroller addon for H-DAC

  • Provides microcontroller interface to H-DAC jumper-link pinheader
  • Can be made Arduino-compatible with external USB-serial interface board

Addon H-MCU is designed to be able to use H-DAC in Quad DAC in place of my old DAC boards. It makes it possible to switch input and DAC filter via external remote signals.


Dual Trafo Board – Small dual transformer board

  • Placeholders for two small, approximately 10 VA, dual-secondary PCB transformers
    • One transformer in series configuration for dual (analog) supply
    • One transformer in parallel configuration for single (digital) supply
    • Independent circuits, no common ground
    • Supports the most common transformer pinouts
  • Fuses, rectifier bridges, and filtering capacitors

Dual Trafo provides three unregulated low power voltage rails for mixed signal devices, such as DACs. The board can be followed by a regulator board such as SmartPSU3 or SimplePSU3 (without filter capacitors) or it can be used to feed application board’s regulators. This 10 by 10 cm PCB can accommodate two approximately 10 VA dual winding transformers, one in series and the other in parallel secondary configuration. Therefore, it can provide at least 200 mA in +15/-15 V range for analog components and few times that in 5 V range for digital supplies.


Simple PSU 3 – 3-channel linear DC power supply

  • Three linearly regulated voltage outputs
    • One dual supply for analog voltage supply
    • One single supply for digital voltage supply
    • Separate grounds
  • Fuses, rectifier bridges, filter capacitors, and regulator circuits
  • 2x LM317, LM337 (or any pin-compatible)

SimplePSU3 contains three simple 3-pin adjustable regulator circuits. Its one dual (analog) supply and one single (digital) supply suits especially well mixed signal audio circuits. Regulators are placed on the edge of the board for mounting on heatsink or chassis.


Smart PSU 3 – 3-channel linear DC power supply with monitors

  • Three linearly regulated outputs
    • One dual supply intended as analog supply
    • One single supply intended as digital supply
    • Common ground
  • Undervoltage, overcurrent, and overtemperature monitor and protection
  • Maximum 1.5 A per channel, depending on the design and cooling
  • Output relays
  • Software controlled (Arduino compatible)
  • 2x LT3081, LT3091, ATmega328P

SmartPSU3 provides three relay-switched regulated and monitored low power voltage outputs. As it has one individual positive and one dual positive/negative supply, it fits well for mixed signal audio applications, such as DACs, where dual analog supply and single digital supply are required. All channels use linear regulators for low-noise output.

The regulators have hardware current limits and on-board microcontroller adds undervoltage and temperature limits. Therefore, hardware-based current limits reacts fast while software isolates the load with relays in case of overcurrent, undervoltage, or overtemperature. Microcontroller circuit is Arduino compatible.


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