Topping is well known for their low-cost audio electronics, ranging from amplifiers to DACs and headamps. They have become increasingly upmarket and their top-of-the-line DAC, the D90 was released last year.
The buzz around the D90 was centered around the decoding chip used, the Asahi Kasei AK4499. The DAC chip alone does not maketh the final output. The quality of the power supplies and the output stage play a part too, not to mention the implementation of the digital receiver, clocks etc.
The AK4499 is Asahi Kasei’s premium offering in their Velvet Sound range. It is described as a 4 channel switched resistor DAC with top-notch measurements like a dynamic range of 137 db (stereo) and THD+N of -124 db.
The D90 MQA DAC is an update of the D90 DAC with MQA decoding and a change of the USB chip from the XMOS XU208 to the XU216. The rest of the features list of the D90 MQA reads like any top-shelf DAC, including fully balanced outputs, DSD 512 decoding, I2S input and dual Accusilicon Femto clocks. The best feature is left for last - a retail price comfortably below USD 1,000 (USD 799.99) !
In a nod to modern conveniences, the D90 MQA includes a Bluetooth receiver, with support for Bluetooth 5.0 and LDAC/AAC/S-BC/APTX/APTX LL/APTXHD protocol. In other words, you can stream 24 bit / 96 kHz music with the right source. If you believe that a receiver and antenna is the work of the hi-fi devil, you can disable the function from the front panel.
The rear panel has all the usual inputs, including Toslink and AES. I2S input is in the form of a HDMI socket, and the pin settings can be configured to maximise compatibility with your source.
Both single ended and balanced outputs are provided. The RCA jacks are spaced quite close, so be careful if you have cables with very large connectors.
Looking at Topping’s internal pictures, a single power transformer is used in the linear power supply (voltage is easily switchable by the user), with lots of goodies like Nichicon FW power supply capacitors, TI OPA1612 chips for I/V conversion, and healthy voltage regulation (including 6 independent regulated power supplies). Bear in mind that all this is packed in an enclosure that is small and light enough to be held in the palm of your hand. The Topping's external dimensions are 22.2 cm x 16 cm x 4.5 cm (W x D x H), and the unit weighs 1.4 kg.
The Topping is a fully balanced design, with two outputs from the AKM4499 DAC chip paralleled to achieve better performance. The AK4118 receiver chip supports up to 24 bit / 192 kHz sampling rates through the Optical, Coaxial and AES digital inputs. USB and I2S inputs support up to 768 kHz sampling rate, as well as DSD 64 - DSD512. The XMOS XU216 chip contains two xCORE tiles with up to 2000 MIPS processing power (double that of the XU208). You may also choose to have simultaneous output from both the RCA and XLR analog outputs, or only have one output active.
The digital volume control can be operated in 0.5 db steps, which permits you to skip a separate pre-amplifier if required. The Topping also has a choice of six FIR digital filters for PCM and two settings for DSD. A plastic remote control is also provided with close to full functionality.
I liked the front OLED panel, which uses large fonts that can be seen across the room. All necessary information is displayed, including the active input and output(s), sampling rate, volume and whether the stream decoded is PCM, DSD and MQA processed.
MQA - A Primer
MQA, or Master Quality Authenticated is a process that was established by Meridian Audio, the well-known British hi-fi company. MQA allows high-resolution audio to be packed into a compact data stream. It also digitally fingerprints files so that you can be assured that your file has not been tampered with in any way.
MQA files are backward compatible with any equipment capable of playing back red-book CDs or digital files, and can be encoded on popular files formats like WAV, FLAC or ALAC. In a process that is termed as "Audio-Origami", the high-resolution signal is folded into either a 44.1 kHz or 48 kHz sampled format depending on the sampling rate of the original file. Lossy compression is applied to the ultra-sonic frequency range (which has little amounts of energy). The most practical benefit to this is reduced data bandwith required if you are streaming (e.g. from Tidal), and much smaller file size.
MQA is also able to do digital compensation to the encoded signal based on the recording equipment. If your DAC has a full MQA decoder, there is also further compensation for the playback device.
The first level decoding (MQA Core Decoder) of the signal enables the signal to be unfolded into a high resolution stream (MQA Core Stream) of either 88.2 kHz or 96 kHz. You may use Roon, or any other compatible software decoder to extract the MQA Core Stream.
The Topping is a full MQA decoder which will perform the full unfolding, authentication of the stream and do file and DAC specific compensation to achieve the highest possible sound quality.
I high recommend watching this video on "The Hans Beekhuyzen Channel" which explains how MQA works.
(To be continued ....)