Audio-gd R28 DAC/amp

When I first joined Head-Fi in search of new headphones, it was rare to find a combined DAC/amp. The ones I recall, made by HeadRoom (which has recently been bought out by Headphones.com) was a magnificent balanced amp with a tiny, very basic DAC card inside. When a local shop came up with their old premium portable DAC amp, I bought it out of curiosity and was disappointed with the sound quality. 

How far we’ve come!  Audio-gd’s combined DAC/amps have long been popular, with the NFB-11 and NFB-28 being something of a standard in their offerings. Some of it is my fault, as they were my suggestion in the first place — a result of both frustration and ignorance. But if my innocent suggestion back in 2008 or 2009 or so ended up resulting in products such as the R28, I have no regrets. 

With the desire to keep producing R2R-based DACs, despite the end of manufacture of R2R chips, Kingwa moved his products towards pure resistor-ladder DACs and all the challenges that come with them. Despite making the R2R 7 flagship DAC, a lot of people wanted a mid-range combined R2R DAC amp — something equivalent to the NFB-28, but with the R1 ladder DAC inside. However with the ladder DAC boards being large, that wasn’t possible using the existing case. 

That is where the new case comes in. Larger than the cases used for the mid-range products, such as the NFB-1AMP, yet smaller and much lighter than the cases used for flagship products such as the R2R 7 and Master 9, the R28 feel neater and less bulky than the other components in my rack, yet still substantial. 

If I were to say that it’s an R1 and NFB-1AMP in a single case, minus one transformer, you could pretty much stop there. But if you’re not familiar, let me delve in with my experience of it. 

Design

Audio-gd R28

The design of the R28, similar to the NFB-28 has both analog and digital inputs and pre-amp outputs that can be hard-switched to a fixed output mode via a button on the back.  This allows use as all of a DAC, headphone amp, DAC/headphone-amp, pre-amp and DAC/pre-amp. 

Balanced and single-ended inputs and outputs are included, though the design itself is balanced (differential) internally, so at least the balanced outputs should be used most ideally, the single-ended analog inputs being converted to balanced inside before amplification.

On the input side, along with 192k-capable optical and coaxial S/PDIF, the included USB and 12S support up to 384k input, handy for those people who like to use or experiment with either very-high-res files or up-sampling. The USB is powered by the input and lacks isolation, making it affected by whatever it is connected to and, as I found, benefits from a good USB or I2S transport. 

While both balanced and single-ended headphone outputs are included, the balanced output is recommended. As a lot of headphones come with a 4-pin XLR-terminated cable these days, it’s fair to say that the R28 is aimed at these headphones.

Audio-gd R28
The relay-controlled volume to the right of a DAC module.

The Sound

Audio-gd remoteThe R28 uses an exponential, relay-controlled volume with three gain levels, which switch through the relay-controlled resistors at different rates. Low, High, and Full allow a good range for everything from IEMs to highly-insensitive headphones like the HiFiMan HE6-SE and Susvara. 

Input control, gain, and the pre-amp/headphone-amp switch can all be remote-controlled via the universal remote included by Audio-gd, which works on many of their products. The “Dig1” through “Dig6” buttons control the inputs of the R28, included the last two analog options. Unfortunately volume control, while possible via the remote, requires a press of the button for each step and will not repeat when the buttons are held down.

While not the main target of the design, one of the areas where the Audio-gd amps shine is their performance with IEMs. Primarily as a noise test I plugged in the very sensitive Campfire Audio Andromedas. Despite a small amount of hum (which may have been a result of the balanced adaptor I was using, as it has a known issue) the R28 drove them with fantastic precision, way more than enough to keep me listening and enjoying the music. 

On the other end of the scale, the inbuilt amp drove my high-end cans, such as the Focal Utopias and HiFiMan Susvaras very competently, if not with quite the spaciousness and ease of detail retrieval that the bigger Master 9 is capable of. Like the NFB-1AMP, the R28 eschews any colouration, driving headphones with a get-out-of-the-way-of-the-music and presenting it as it is. That ability to accurately drive even tricky IEMs means that even the treble of bright headphones comes through with a clean, but not artificial smoothness.

Audio-gd R28
A DA-8 R2R DAC module

On the DAC side, just after I received the R28, Kingwa contacted me about the firmware, to tell he had a new version he’d created. I gathered that there were similar versions for the R2R 7 and reports about that suggested it was a significant improvement. Prior to that one had a choice of “smooth” (the default) which sacrificed a bit of detail for musicality.

The other was “Accurate” which improved the accuracy of the output of the DSP to the DAC modules, but introduced some 3rd-order harmonic distortion making the sound more lively, but too aggressive for some. Other firmware either increased soundstage but lacked depth, or increased depth dramatically, while the soundstage narrowed. The new firmware seems to solve the issue of keeping resolution yet also sounding musical.

The way the DAC in the R28, like the R2R 7 which I reviewed before it presents music, is what makes it a delight to use either as a DAC, or a DAC/amp. There is a great sense of both musicality and detail, either of which are often sacrificed in competing designs. The Yggdrasil (Analog 2) in comparison, while ultimately more detailed, sounds a little dry, whereas the R28’s musicality made me want to listen more and more.

In non-oversampling mode, engaged by putting a jumper on a set of pins under the lid (visible just below the DAC module in the above picture) the sound tilts towards that of class “NOS” DACs — a more syrupy presentation that sacrifices detail and soundstage for musicality. Given the already “warm” presentation of the unit in oversampling mode I felt that this was unnecessary. However for those who wish to tweak, the unit can also set to 2x and 4x oversampling, alongside the default 8x. 

In my case, I took advantage of the 384k-capable USB input and could increase the precision of the sound without sacrificing musicality by up-sampling with Audirvana Plus, bringing the R28 a bit closer to the detail of my main DACs.

For people who want even more warm, there is a set of jumpers on the analog output stage that tilt the sound even further from neutral, though I didn’t try them.

The difference in sound quality between using the R28 as a straight DAC (which can be done in pre-amp mode with loss of clarity thanks to the volume system) was only behind the top-end DACs I have here (Yggdrasil Analog 2, Hugo 2 and iFi Pro iDSD) to the degree that my Power Plant Premier, iFi iUSB 3 and Audirvana could push the R28 up to the point that I couldn’t tell them apart using the Master 9 amp for output.

In other words, the jump from the R28 up to an Yggdrasil/Master 9 system was not that great at all, especially with most of the music I listen to, which doesn’t always contain that much detail to begin with.

Likewise, as a DAC/amp it cannot compete with the magic that the Hugo 2 can give directly to headphones, not surprising with the advanced design behind it. However, given the $3700 cost of the Yggdrasil/Master 9 combo (excluding extras), or even the $3000 cost if the R8 DAC is used instead of the Yggdrasil, the $1038 cost of the R28 makes it a heck of a bargain.

A poster on Head-Fi stated that the R28 was his “end-game” device and I am not surprised. The R28 is a very musical and enjoyable device with a great feature set. Future iterations will likely include the ability to switch filters and modes on the front panel which will increase the convenience of its versatility.

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