Audio-GD R28 Review by Currawong
HIGHLIGHTS
- Sample rate display indication
- USB with fully integrated with internal FPGA deriving clocks from Accusilicon’s (similar to DI20 architecture)
- Dual 32 bit parallel signal processing (FPGA) on I2S / USB inputs
- Dual 24 bit parallel signal processing (FPGA) on SPDIF inputs
- DSD asynchronous clock technology (significant sound improvement)
- Dual transformers power supply separately.
- Full new configuration clock manage design built in, improved on the clock timing.
- DSD asynchronous clock technology has apply that improves the sound quality obviously.
- DoP support from coaxial input .
- The unit has two gain modes, the 12DB on low gain for drive the headphone which has over 95DB sensitivity, and 22DB on high gain cooperate with the strong power ability, enough to drive the HE6 which has around 85DB sensitivity headphones.
| SPECIFICATIONS | |
|---|---|
| Type | Pre-amplifier / Headphone amplifier with integrated R-2R DAC |
| Inputs |
|
| Outputs | RCA / XLR / ACSS |
| SNR | >120dB |
| Gain | L : +7dB H : +17dB F : +17dB |
| Volume | 100 steps super exponential control |
| Channel Imbalance | <0.05dB |
| Frequency Response | 20Hz-20kHz 1Hz – 140kHz (-3DB analogue) |
| Output Level | Headphone 19v RMS Variable Output : 10V RMS Fixed DAC Output : 5V RMS |
| Headphone Output | 9500mW / 25 Ohm 8000mW / 40 Ohm 3500mW / 100 Ohm 1200mW / 300 Ohm 600mW / 600 Ohm |
| Output Impedance | ACSS : 1 Ohm DAC / Preamp : 5 Ohm |
| Input Sensitivity | 0.5Vp-p (75 Ohms, Coaxial) 19dBm (Optical) |
| Support OS | Windows (driver), OSX, Linux, ISO |
| Sample Rates | USB : 44.1kHz, 48kHz, 88.2kHz, 96kHz, 176.4kHz , 192kHz, 352.8kHz,384kHz COAX : 44.1kHz, 48kHz, 88.2kHz, 96kHz, 176.4kHz ,192kHz Optical : 44.1kHz, 48kHz, 88.2kHz, 96kHz, 192kHz |
| Power | 220-240V AC50/60Hz |
| Power Consumption | 33W |
| Weigth | 7.5Kg |
| Dimensions | 360 x 360 x 85 mm |
| Accessoires | IEC Power Cord x1 USB Cable x1 Remote Control (plastic) |
THE R-2R LADDER STORY
The R-2R DAC has become popular and was originally designed long time ago by MSB, and did not include the wonderful correction design of the modern MSB technology. In the High-End of the shelf (finished products) market, the R2R design is usually much more complex when outstanding performance is offered. Some manufacturers are using shift registers design to realize ladder compensation. A less complex, unfortunately also a less performing.
A far better design switches resistors in parallel mode; an ultra-fast FPGA chip controls and corrects the R2R ladder. The parallel design mode controls every bit respectively and therefore achieve unprecedented performance. (In parallel mode only 1 clock cycle is needed to output all data; serial design mode needs at minimum 8 up to 24 clock cycles) The parallel design is particularly complex, however when it is done properly it can correct every bit of the ladder. (Photo below shows a FPGA design with R2R ladder). With incredible speed and accuracy the R-28 will correct the unavoidable imperfections of the basic R2R ladder caused by tolerance of resistors; avoid glitches at ultra-high speed to deliver unrivaled musical performance.
TOLERANCE OF RESISTORS IN LADDER
Some manufactures claim to achieve good performance becuase they use lowest tolerance ladder resistors. The following calculation example will cover this. At 16 bit the tolerance of 1/66536, 0.1% (1/1000) it is by far not enough to achieve decent performance. Even using resistors with 0.01% (1/10000) tolerance, lowest tolerance available today,cannot deliver the desired performance This is just 16 bit, imagine a 24 calculation! To process 24 bit resolution it would require resistors with a tolerance of 0.00001%. This is purely theoretical; if this tolerance would exist the discreteness of the switch logic chips will already have too much internal impedance and will shake-up such design.The tolerance of the resistor will never solve Imperfections of a ladder.
The solution lies in the correction the ladder and not only depend on the tolerance of resistors. It’s a combination of both: Ultra-low tolerance resistors controlled by a correction technology using very high speed with parallel FPGA processing.
ULTRA FAST SIGNAL PROCESSING
FPGA stands for Programmable Array Logic. Nowadays the FPGA is widely adopted in audio devices. The internal hardware design is fully controlled by complex software. A huge advantage is the fact the software in the FPGA can easily be upgraded offering new capabilities or improve the performance of the device without replacing any hardware. Versatile and future proof design.
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- High performance SPDIF interface, replacing traditional less good performing SPDIF interface chips like DIR9001, WM8805 or AK411X,etc.
- Full re-clocking process with FIFO design applicable on all inputs. This way the output data keeps fully synchronized with the clock signal to reject any jitter.
- Built in 2X, 4X and 8X oversampling and digital filters and on top of this 4 different true NOS (only analog 6dB filtering) modes. To completely configure the sound according to your taste.
DIAMOND ANALOGUE OUTPUT STAGES
The analog output stages are as important, they have a tremendous influence on the final sound quality. After d/a conversion by the R2R D/A modules the analogue signal is transported by fully discrete matched-transistor output stages; DC-coupled design with first class through-hole components. No SMD compon ents are applied in the analogue section. The high speed unique ACSS ((Audio-gd Current Signal System) output stages are non-feedback and current driven. Unique performance because almost all other designs need to convert the signal multiple times from and to current and/or voltage, resulting in less detailed and less transparent sound-stage The output buffers are single ended FET; two stages in parallel to reach very low output impedance. All output stages are in pure class A without (negative) feedback to achieve purest and a real live sound reproduction. The 4 OPA op-amp’s are DC servos, this way no coupling-capacitors are needed and DC output is automatically biased. The listener will be presented a strikingly transparent and neutral sound.
HIGH PRECISION VOLUME CONTROL
Volume control consist of relay-controlled attenuators. Fully-independent, fully-balanced stereo volume controls. The volume controls feature consist of high-precision 0.05% tolerance film resistors and golden contact relays. Buffered inputs and outputs.There 4 channels volume boards are built in the unit to achieve ultimate balanced volume control. They are controlled by a digital signal controlling the high quality relays switching the precision resistors in analog area.
Quality of volume control is very important in balanced applications . It have to effectuate the four channels to work as synchronous as possible to keep the balanced signal in perfect shape. In traditional volume controls the balanced output will introduce distortion which will negatively influence sound quality and performance and might even get worse than a single ended setup and waste the advantages of balanced designed solution.
CLEAN POWER
The DAC consist of 2 tuned low noise, low flux leakage, R-cores transformers. In total 130W power to supply all digital parts and the left and right analog boards. The DC power is distributed over several separate power regulators. Analogue stages are pure class A low noise shunts; fed by 3 groups linear power supplies. Resulting in ultra-high speed and clean power for all individual parts.
Andrea (verified owner) –
Bought the R28 2022 version: what a purchase! I regrettably no longer have the HE6SEv2 and I bet this beast would drive those as a charm. The DAC portion of the device is also very satifying and it took me a bit to get uesed to it (brain or hardware burn-in? I will never know…). Coming from a Violectric V200 I thought I was akready enjoying a warmer than average sound delivery but this takes it to another level.
I have yet to decide if I prefer NOS or OS. The effect of the vynil record simulation, which is suppposed to provide the smoothest setting, isn’t yet clear to me and I don’t hear much of a difference. Using it mostly with HD800S and Arya Sealth Edition. It also proved an outstanding match for my Beyerdynamic T90 whos high register is less extreme with this amplifier than it is also with a (modest) tube amp such as the Little dot mk III, which I am now selling. Indeed it seems that the same sonic results of OTL tube amplification can be obtained by the R28: not sure if it is just due to the R2R decoding or if also the amplifier plays a role.
Great service from Magnahifi is the icing on the cake.
Valeri V. (verified owner) –
It is outstanding DAC. Sound quality is amazing. I use model of 2022 as DAC/preamp with Nelson Pass’s amplifier Aleph J connected via XLR output.
I also satisfied with service of Magna Hifi.
Leon (verified owner) –
After few days of listening I have to say that I am very satisfied . It sounds very musical and relaxed in a good way with a good soundstage. I tested with my lumin streamer via coax and usb. Both sound really nice.
Frank –
I already had good experiences with this brand, especially with R2R DAC’s, but I did not expect this upgrade. Really great sound through my headphones. I also use the preamp output. This works best with XLR, with RCA I suffered from slight hum. I am very pleased with my musical friend!
Steve –
My R28 arrived back to me this morning, thank you. Straight out of the box my system sounds very much improved, I have the R28 hooked up to a GRAAF GM 50B MK2 Integrated. So many thanks for you help and expertise, I look forward to doing business in the future.
Steve P. –
Hello Magna Hifi!,
I am very much enjoying the Audio GD R28 DAC/Pre I purchased from you.
Thank you very much for your excellent service.
Steve P.
Peter S –
Today I received the device and seriously, my hands are shaking while I am writing this letter to you. I know that you said that the burn-in period is 2-3 weeks but we just couldn’t hold trying it with my girlfriend.
I played classical music and brass music mostly for 15 years to the point that I can’t listen to classical music anymore but today we picked up some old favourites, set up the device and played them while sitting in the sweet spot. We just kept listening to the music without talking and we both felt that we start to cry if we don’t hold it back.
I read a lot about Audio GD in the last few days and I found those bad reviews and measurements that I am sure you also know. I graduated as an electrical engineer and I can read those measurements and I admit I even thought about canceling the order but so good that I did not! Even if the measurements are not good as other devices on the market, it is beyond dispute that the sound is fantastic!
It is already fantastic without burn-in, the sound of the instruments are so real, it is unbelievable! Thanks again for the fantastic device and the discount! You got a fan! If it helps your business, I am more than happy to write a review anywhere and I am going to recommend you to my audio friends!