Thursday, May 21, 2020

Topping D90 MQA DAC


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 premium 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 RCA plugs. 

Easy access to the voltage selector at the bottom of the unit.
Looking at Topping’s internal pictures, a single power transformer is used in the linear power supply (the mains 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. USB decoding is handled by an XMOS XU216 chip, which 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. The remaining functions can be accessed by pressing the left button and switching on the unit. 

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. The brightness of the display can be controlled, but not switched off entirely - take note if you are an audiophile bat.

Build quality is impressive and the look and feel of the Topping far exceeds my expectations, especially at its price level.  

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 then 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 apply file and DAC specific compensation to achieve the highest possible sound quality. To be clear, no software decoder is required for full MQA decoders, and MQA encoded files can be played from any source. In my case, the files were streamed from my Melco N1/ZH2 NAS and TIDAL. For users that do not own a DAC with MQA decoding, a software decoder upstream will at least allow them to enjoy high-resolution audio, but without the final unfolding to either 172.4 kHz or 196 kHz sampling, nor DAC compensation.    
I high recommend watching this video on "The Hans Beekhuyzen Channel" which explains how MQA works. 

Sound Quality

In comparison to their upmarket relatives, my experience is that budget to mid-range DACs generally lag behind in microdetail retrieval, low frequency authority and dimensionality. They do deliver most of the goods, but that fraction left on the table is what motivates audiophiles to open their wallets.

Serious listening was done after a week of burn-in and experimenting with the different inputs (I'll come back to that later).

The Topping delivers very good sound quality with excellent detail retrieval. It has tight bass which is delivered with punch when required. Midrange reproduction is good with a sweet tonality that is comfortable to listen to. High frequencies are extended too, with a sparkle and decay that is able to recreate a spacious and convincing portrayal of the acoustic space of the recording. Its star quality to me is staging and imaging, which is done with very good depth, width, and space around voices and instruments.

I would describe the Topping as tonally close to neutral with a touch of warmth. The staging and vocals have a laidback character to it, while transients are clear but with a soft edge to it. If you like your music to have a crisp snap and edge, you are probably not going to like the Topping. 

The Topping likes to play nice, and the softer presentation does flatter poor recordings, especially bright and harsh ones. I actually find this to be a desirable character, considering that the Topping will most likely be used with other affordable equipment, which may have weaknesses and flaws best not laid bare for all to see.    

I also did some listening tests to sample MQA files available from 2L. I preferred the MQA encoded files of both the original high-resolution recording, and the CD quality file. I was not sure about the merits of MQA prior to this, but consider me sold.   

As good as the Topping may be, it is not going to dent the sales of high-end DACs. While it does embarrass a lot of the competition, as well as many mid-range DACs, the Topping is unable to match the best out there in detail retrieval, dynamics and other audiophile niceties that the enthusiast seeks. To be clear, I am very comfortable recommending the Topping for the price, and even if your budget is a multiple or two of that. However, don't rush out to sell your flagship DAC in favour of the Topping !

A Word About Inputs

I have a general preference for using SPDIF over USB inputs, relying on an outboard USB / SPDIF bridge as I find it delivers better sound quality. In the case of the Topping, the USB input was superior, with SPDIF sounding a bit more gray and vague. I use a Weiss INT204 bridge, powered with an Uptone JS-2 power supply. It was a surprise then that the much simpler (and cheaper) route sounded better.

I also tried connecting my Melco N1/ZH2 NAS to the I2S input of the Topping using a Singxer SU-1 USB / SPDIF bridge. Despite careful study of the pinouts of the Topping, and appropriate setting of the DIP switches on the Singxer, I was unable to get any sound although the appropriate sampling rate was displayed on the Topping. 

The Bluetooth connection actually works quite well, and I was very comfortable using my Samsung Galaxy S10+ phone to stream music from Tidal to the Topping. The quality is more than decent and the slight loss in quality is more than acceptable. 

Most of my listening was done using the USB input.


While switching from non-MQA to MQA encoded files, there was a brief, but loud burst of static through my system. The Topping locked-up on the two occasions that it happened, and the unit had to be powered down and restarted before everything was back to normal. I was not able to recreate this again, and I am unsure whether the problem lies with the Topping, or the rest of the equipment in the chain. Do leave a comment on this post if you have had similar experiences with your Topping.


The Topping D90 MQA is an excellent way to get your feet wet in the MQA pool for a modest outlay. I am pleasantly surprised at the very high quality delivered for the price and this is definitely an outstanding value-for-money product - Best Buy

P.S. The Topping was a personal purchase by me at full retail price. 

Second Opinion (From TC)


I was pleasantly surprised when i received the package from Eric. It comes in a large black cardboard box with the words "TOPPING" on top. The DAC is snuggly fit in between the thick foam compartments and it would survive any kind of rough handling during shipment. The DAC is the most light weight and smallest that i have come across in this hobby with the Calyx 24/192 coming in second place in terms of size but on the other hand very heavy due to the casing.

Being conditioned that bigger and heavier equipment means more good stuff are packed inside, frankly when i lifted the Topping i thought "is it really as good as what all the reviews say ?" With the D90 placed on top of the Oppo 205, i hooked it up and started playing songs using the Cambridge Audio CXC as a CD transport. I sent a photo to Eric and promptly got a reply back that the DAC looks like it's floating! I looked closely and realised that it's front is being lifted up due to the heavy power cord it's connected to. I removed the Oppo 205 from the rack and placed the DAC back on the rack space this time ensuring that the DAC is fully resting on the rack shelf and powered it on. Wow! the sound is lifted up by a few notches right away! Important tip to note. Though the Dac is small and lightweight, it's still sensitive to placement and deserves a good spot in your rack and try not to stack it on top of other equipment to get the maximum potential out of it.


True to the AKM "Velvet Sound", the DAC does sound very refined and smooth without any rough edges. Music flows like a water stream and you can just sit back and let the DAC perform its magic. 

Be patient and let the DAC warm up at least 30 minutes and you will be rewarded with spades of details and layering. Bass is tight, in control and not excessive. It's not a forward sounding and grips you in the seat type of sound but i would say the character is an even handed with a deep soundstage. As i keep listening to the DAC, fluidity, naturalness and musical comes to my mind.  

Just for the fun of it, I have tried to tweak the sound with the cloned Ceraball footers but find that it tipped the high frequencies too much and wasn't to my liking. Overall, the presentation is still neutral with just a tinge of warmth.

Other comments- despite its small size and light weight, resist the temptation to stack it on top of other equipment to save space. It's sensitive to placement and deserves a proper spot on your rack. Warm up is critical and give it at least 30 mins to let the music soar!RCA cable users might face problem with the tight spacing between the connectors

At this price point, it's a very good performance DAC with a myriad of connectivity options and is even able to handle MQA.

The D90 is highly sensitive to the source equipment that it pairs up with. Compared to the Cambridge Audio CXC, the sound quality coming out from the Mac mini is still very good but just a tad softer and rounded. Layering and micro details are not as transparent but overall
it's still highly enjoyable if you are not out to "dissect" the music. The bass attack is strong and big. I think a dedicated streamer will do more justice to the D90.

I was unable to to turn on the Bluetooth until i sought help from Eric who informed me of the magic menu that will appear when you press the standby button together with the power switch behind the DAC. So for anxious users like me who just like to jump headon to test the DAC without reading the instruction manual, please take note. The Bluetooth function is highly interesting and all you need is your mobile phone. Detecting the D90 on the mobile phone is a breeze and it brings with it a myriad of music sources at your disposal. You could
stream Tidal, Spotify, music files on your mobile and even local radio stations. 

Music quality is slightly below using mac mini but it ups the fun and convenience factor. All you need is a mobile phone, D90, a power amp and you are good to go. Just think of the space that can be saved with a simple setup like this. I have tried out the connectivity distance and i could achieve about 10 metres before I experienced sound dropouts streaming FLAC files. That's quite good already if you like to move around your house multi-tasking doing chores while you listen to music to keep the boredom away.

Final words

The D90 impressed me greatly with its small form factor, multi-functionality and very good sound quality for its price. It banished the common thinking that for good sound quality, the equipment must be big and chock full of components inside. If i could reverse my audiophile
journey a few years back and not be "burdened" with so much equipment, I would get this in a heartbeat. 

Just maybe, if your girlfriends and spouses (Note from Eric - I advise only having one girlfriend or spouse at a time please !) can see how small this D90 is, they will surely "approve" the indulgence in this hobby right away !

Sunday, May 3, 2020

Bottlehead Crack and Bottlehead S.E.X. Headphone Amplifiers


COVID-19 and the lockdown making you sing the blues? Maybe it's time to get out your soldering iron, and start building a kit that you had your eyes on? That's exactly what I did - my poor Bottlehead S.E.X. kit has been collecting dust since I ordered it sometime last year. 

Bottlehead is an established company that has been offering vacuum tube kits to audiophiles since 1995. Their product range covers a wide variety of tube equipment, as well as a speaker kit. 

While kits are not for everyone, I encourage every audiophile to at least try assembling a kit at least once. A lot can be learnt from the experience, including soldering, basic circuit design, patience, and the ability to use swear words in ways that you never thought possible. 

On a more serious note, immense satisfaction can be obtained from building something that you can truly call your own masterpiece. Photos of builds around the world show that audiophiles are a pretty talented lot, with some builds exhibiting build techniques and wood / metalworking quality that can put even professional companies to shame.

As an educational process, I probably learnt more from DIY work than anything else. Mistakes in assembly or poor construction technique will teach you many things, including the importance of good grounding practice, and the importance of proper wire routing.

Bottlehead kits are far from being the cheapest on the market, but their builds are guided by very clear instructions with lots of pictures. They also have a very supportive online forum where you can find a lot of tips and suggestions for modifications. If you encounter problems, the folks there are helpful and willing to go the extra mile to ensure your build is successful.

Introduction to Crack 

This type of Crack is legal around the world and no need to risk your liberty or health to enjoy this. 

The Bottlehead Crack 1.1. OTL Headphone Amplifier kit is described as a Level 1 kit, perfect for first time builders, involving an evening or two of build time. The cheeky name is a common trait across Bottlehead products - they believe that their products involve feelings of euphoria!

The circuit of the Crack is simple, with a low parts count. The power supply is a C-R-C-R-C design, so no chokes to complicate your life (and more importantly, bump up the cost of a starter kit). A lone 12AU7 tube is directly coupled to a similarly lonely 6080 tube used as a cathode follower. As both tubes are dual triodes, each triode section handles one channel. 

There is no output transformer (OTL means Output Transformer Less). Tube designs typically need an output transformer to match the high resistance of the tube output stage, to the low impedance load being driven, e.g. a loudspeaker or headphone. The choice of the 6080 tube (which has a relatively low plate resistance), allows the omission of an output transformer provided that the matching headphone has a high impedance. The Crack has an output impedance of 150 ohms, and is recommended to be paired with headphones of 200 ohms or higher. Parts quality is decent with nothing fancy save for the ultrafast rectifiers. The two most obvious cost-saving measures are the electrolytic output coupling capacitors and the cheap carbon potentiometer.

The Crack can also be upgraded with the Speedball upgrade kit, which is a constant current source supply for the plate of the 12AU7 tube, and the cathode load of the 6080 tube. A similar upgrade kit is also available for the S.E.X.   

Introduction to S.E.X.

This is a family-friendly blog, and this is one three-letter word that can be legally enjoyed with the whole family. Like Crack, S.E.X. is a two-stage circuit. Version 3.0 of the S.E.X. uses a 6FJ7 tube. If you have never heard of the 6FJ7, that makes two of us. The 6FJ7 is a dual triode with dissimilar sections fitted in a Compactron envelope. Described as a TV oscillator tube, this is not a tube that you will be fighting over with other audiophiles.     
The S.E.X. is a substantially more complicated build compared to the Crack. I took more than four evenings to complete the kit, taking my time to carefully check the instructions, and building the kit at a leisurely pace. The S.E.X. has five transformers, consisting of one power transformer, two output transformers, and two plate chokes. Unlike the Crack, the S.E.X. is able to power sensitive speakers, with 2W on tap. 

After completing the kit, I admired my extremely skillful soldering, powered up everything, and music flowed forth like voices from Heaven. The truth of the matter is that I could not pass the resistance tests as set out in the instruction manual and had to go to the Bottlehead Forum for help. Bottlehead's Paul Birkeland noticed almost immediately that one of my ground wires was not connected and all resistance tests passed after I fixed that. Interestingly, I had no plate voltage on one channel. Checking all connections carefully with a magnifier and torchlight showed that one of my connections had not yet been soldered. Some of my sloppier solder joints were re-flowed and everything was good after that, or so I thought.

I switched on the S.E.X. only to be greeted by loud popping and static from one channel. This was puzzling since I was pretty sure that all issues had by now been addressed. After swapping interconnects, I realised that the sound would stop when I gently tapped the chassis near the left tube. I removed the left tube and after a few sharp taps to the envelope (please do not do this to a hot tube), it was quiet - time to look for a replacement tube.      

Build Experience

I bought the Crack pre-owned, and it came with the Speedball upgrade already installed. So, my experience relates to my build of the S.E.X. kit.

Thanks to the excellent instructions and well-thought-out kit, assembly of either kit should be achievable, even for the novice who cannot read a circuit diagram. However, understanding the circuit makes things a lot easier, as well as good soldering techniques. Neither of these kits is in my opinion suitable for a person with no soldering experience, nor a basic understanding of electronics. My suggestion is for the inexperienced to do some basic reading, and practice stripping wires, trimming parts and soldering some waste or spare components on a practice board.

The instructions are also catered for the world of Imperial measurements. I had absolutely no idea what a number #4, #6 or #8 screw size is, although to give Bottlehead credit, some of these parts are listed in the instructions with metric dimensions.

It also pays to be very attentive when reading the instructions. As multiple connections may be made to a single terminal hole, you have to make sure that you only solder the point when asked to do so. Despite taking my time, I made this mistake a few times. Thankfully the terminal strips have plenty of space for fixing these mistakes.

Due to a mistake made in stripping the supplied ethernet cable (used for signal hook-up), I had to use some spare Canare star-quad microphone cable to run from the RCA sockets to the potentiometer. Otherwise, I used all the parts as supplied. The carbon potentiometers could have better tracking, and show noticeable channel mismatch at very low volume levels. At practical listening volumes, the channel tracking was acceptable.  

Sound Quality

In today's episode of Spy vs. Spy, will White Spy (S.E.X.) or Black Spy (Crack) emerge triumphant? 

To give both spies a level playing field, only two high impedance headphones were used - a Sennheiser HD6xx (300 ohms) and a Beyer DT-880 (250 ohms). Both spies were sent on physical training camps and a few simple missions to ensure that they were in tip-top condition. 

Black Spy by virtue of its creamy and wet midbass will win over a lot of fans. I thought it would make the Sennheiser sound too dark, but it actually worked quite well. For the brighter sounding Beyer, it added fullness and heft to the sound. Black Spy was not the most meticulous or detailed of spies and glossed over some details. However, if you have an aversion to thin, bright and etched recordings, Black Spy will be your best friend.

The Crack is not tonally neutral. It adds a pleasing warmth to your recordings and takes an edge off all the nasties. Bass control is a bit loose and if you favour fast-paced rock or EDM tracks, this is probably not the best choice for you. 

White Spy, on the other hand, is leaner, faster, and a lot more detailed. The immediate thought that strikes you is, "Where did the bass go?". The bass is taut, tuneful, and very controlled with no flab. I actually appreciated the detailed and articulate bass lines of the S.E.X. 

In similar fashion, vocals are more open and textured, with a deeper insight into the recording. The neutral approach also means that your enjoyment will be dependent on the quality of your recording. My only criticism of the S.E.X. is that I did find myself missing the bass impact of the Crack. A half-way house between the two would have been perfect. I will revisit how the S.E.X. performs after installation of the CCS upgrade kit. 


Which kit is best for you ? My thoughts on this :-


  • First-time builder
  • Preference for a warm and forgiving sound
  • To be paired suitable headphones (>200 ohm impedance)

  • Second-time or advanced builder
  • Preference for a faster and more neutral sound
  • To be paired with a variety of headphones, including low impedance models
  • To be paired with sensitive speakers 

A select few listeners would prefer the Crack over the S.E.X. I personally think the S.E.X. is worth the extra cost for a more sophisticated sound, better transparency, and more flexibility with partnering equipment. 

Bottlehead Crack
USD 315 or 430 with Speedball Upgrade

Bottlehead S.E.X.
USD 539 or 574 with C4S Upgrade

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