Our principal engineer has over 25 years of experience on very low noise mix signals (integrated digital and analog) systems design. He has been an audiophile since the mid 1970s. So, he knows well how an excellent audio amplifier should sound.

In the board level design of the Soundberry Audio’s amplifier boards, our engineer has implemented galvanic isolated ground plane for the analog circuits. This effectively keeps the high frequency noise from the noisy computer board getting into the analog audio amplifier’s ground plane. Furthermore, he uses switching mode power supply instead of bulky linear transformer to eliminate the hard-to-remove residue 50/60Hz a.c. line frequency hum. Yet, he has never worried about the high frequency noise getting into the audio signals simply because ripples with 50kHz and higher on the DC power supplies lines are easy to be filtered out.

On the component selection, our engineer has chosen the ultra-low-noise ultra-high PSRR LDO voltage regulator LT3042 made by Linear Technology for the extrememly quiet low voltage DC supply to the DAC integrated circuit chip. Please be informed that the ultra-high PSRR feature is the key to kill the high frequency noise and ripples effectively from the switching mode power supply. In addition, he also uses low thermal noise thin film resistors in the analog signal path and the superior sound quality ultra-low-noise ultra-low-distortion bi-polar input OpAmp OPA1602 to keep the playback music sound natural.

Our engineer is very creative to use a pair of audio grade transformers to drive high impedance headphones. Headphones with impedance range 250 to 600 Ohms will be good match. According to the transformer’s data sheet, the frequency response between 30Hz to 18kHz is surprisingly linear. In addition to producing warmer and richer sound, the balanced driven headphone transducers are completely isolated from each other. The use of NDIC 4.4mm balance stereo phone jack allows users easily find affordable aftermarket silver plated cables to upgrade their headphones. The volume control has a build-in switch. It is used to switch on/off the amplifier circuit. When the amplifier is powered off and the Raspberry Pi board is on, the music files stored in the SDCARD folder can be shared with other Soundberry Audio Network Streaming Players.

We have auditioned our HPA02A against a famous brand name Class-A headphone amplifier model HA-501, our HPA02A matches the sound quality, and sounds warmer and richer than the HA-501 when the transformer output phone jack is chosen.

HPA02A Balance Output Headphone Amplifier with Transformer Output

In the PA90 amplifier design, our engineer has chosen the very popular amplifier chip TPA3116D2. If the application circuits for the TPA3116D2 is well implemented, the Class-D amplifier can sound exceptional good. During the hardware development, we used our Art Audio Carissa SET 845 pure Class-A tube amplifier and a pair of Dynaudio Contour 1.3 SE for bench marking the sonic characteristic of our PA90 amplifier. While the DAC section design is shared with the HPA series amplifiers, its outputs are converted to balance signals by a quad OpAmp OPA1604 to drive the TPA3116D2 for maximum performance. At the output ends, each of the amplifier’s four outputs is connected to the terminal with short segment of copper track in series with ferrite bead instead of LCR filter. We also use conductive polymer hybrid aluminum electrolytic capacitors for its very low ESR and high reliability. This type of capacitor outperforms the traditional aluminum electrolytic capacitor for switching mode power supply ripple filtering application in Class-D amplifier. As a result, the PA90 produces detail trebles, warm mid-tone, clean and tight bass.

PA90 90W Output Inductor-less Class-D Power Amplifier