What is it?

High resolution audio (24bit/96kHz) capable USB bus-powered Nutube headphone amplifier

Why did you make it?

I have made my first high-resolution capable USB-DAC embedded Nutube amplifier but after finishing the one, I got to know Asahi Kasei's high-end audio DAC has a good reputation. Naturally I improved my circuit with this DAC!

What makes it special?

• High resolution DAC (Asahi Kasei AK4493) with USB-I2S receiver (SA9023). This nice combination provides maximum 24 bit resolution with 96 kHz sampling rate.

• The AK4493EQ is a new generation Premium 32-bit 2ch DAC with VELVET SOUND™ technology, achieving industry’s leading level low distortion characteristics and wide dynamic range with six types of 32-bit digital filters, realizing simple and flexible sound tuning.

• The function of AK4493 can be controlled through Arduino sketch, together with on-board Arduino boot loader loaded Atmel ATMega88PA. The default firmware sketch is uploaded to my Github. Detailed function implemented in AK4493 is explained in the datsheet. In order to upload your own audio setting written by Arduino sketch, USB-UART interface (CP2102) is included in this item. Yes we have a joy to tune sound!!

• Full USB bus power. Just connecting the USB cable (mini USB) is enough to drive everything. Careful PCB layout design with several DC line filter, no annoying noise related with USB line. On-board 1.6 MHz (no audio interfere) voltage booster creates high voltage for Tube and Op-amp operation.

• Wonderful Nutube sound. It looks like VFD but really double triode, provides mellow and marvelous vacuum tube sound.

• MUSES8920 , the high-end audio op-amp also works as the impedance converter.

• Texas Instruments's SoundPlus™ High Common-Mode Rejection, Low Distortion Differential Line Receiver INA1650 is applied between AK4493's differential output to Nutube amplifier part for minimize noise and maximize AK4493's sound.

• No need to install driver for Windows/OSX. Just connect cable and set the sampling rate/bit resolution to 96 kHz/24bit is enough to enjoy High-resolution sound!

• The fully completed and tested PCB board is fit in the fully drilled metal enclosure. USB-UART interface (CP2102) is included for uploading your own customized Arduino firmware.

iPhone (or any smartphone and iPad) operation is NOT supported with this amplifier due to power draw increase. Only PC/Mac operation is supported.