Unbelievable value, arguably the best bang for buck all in one unit. Incredible "NOS tubelike sound." Basically this is a more cost effective integration of the R1NOS DAC + M19 headphone amp- sound is beautiful and powerful enough to drive anything.

I bought to drive Hifiman HE1000v2 but sold that as it was triggering TMJ, fatigue and Tinnitus. Now I have no need for this beast and could use the cash.

Condition is basically brand new, other than recommended manufacturer burn-in ~350 hours. Includes transferable warranty for US service through mid-February 2026.

Sold as-is. Buyer pays shipping.
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Summary

R-28 NOS from Audio-GD is an all-in-one device. A high-quality R-2R Non Oversampling (NOS) DAC , discrete, dc-coupled and balanced design, can be used as a DAC and as a pre- and/or headphone amplifier.

• Discrete & DC-Coupled balanced design
• 8x discrete R-2R DA Converter circuits
• 4x Discrete native DSD decoders circuits
• Amanero USB interface up to 384 kHz PCM / 512x DSD native
• Isolated digital inputs
• Discrete dc-coupled current signal transmission design without opamps
• True balanced headphone amplifier 9.5 Watt max output power, can drive any heaphone
• Eas firmware update to support future improvements and features

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Details

The R28 NOS is a Fully Balanced solid state preamp with 9.5 watts per channel headphone amp and a resistor ladder DAC.

The R28 features 8 fully discrete R2R DAC modules to combine into a real balanced push/pull digital decoder as well as 4 fully discrete real balanced DSD native decoders. The DAC uses two 90/98 MHz Accusilicon 318B femto clocks to provide ultra low jitter.

The Amanero USB input supports 32bit / PCM384K PCM and up to DSD 512 asynchronous transfer. Clocking is done by a custom programmed FPGA. The whole digital circuit is built around one custom programmed FPGA and 5 CPLD programmable chip sets to separate the different circuits for avoid any interference in the data process in parallel mode.

The R28 headphone amp has two gain modes, 12DB in the low gain position to drive higher efficiency headphones at over 95dB sensitivity, and 22DB on high gain with the full 9.5 watts to drive any lower efficiency phones such as the HifiMan HE6 at 85dB efficiency.

The custom internal software that runs the unit is upgradable to improve sound quality in the future. All digital process mode settings are accessible by buttons on the front.

An upgraded metal remote is included ($45.00 value) with purchase. The analog output stage is superb and has a tremendous effect on any DAC’s sound quality. After the D/A conversion by the R2R D/A modules the analog signal is run by fully discrete matched-transistor output stages. These high speed special ACSS output stages are zero-feedback and a current driven design as opposed to the voltage design of most other DAC’s. They are Special because almost all other designs need to convert the signal multiple times from and to current or voltage, resulting in less detail and a less defined sound stage.

The Output stage in the R28 has 4 pairs of 15W transistors to offer tremendous output capability. This Diamond Differential design avoids switch distortion. It works in full Class A mode but doesn’t draw large idle current. This balanced drive design lowers noise and distortion and improves the sound stage presentation and transparency.