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George 47

Chord Electronics Qutest

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Teams or individuals?

Designing audio is unusual in that some products are designed by gifted individuals and others by a large team who pool their skills. Examples of the gifted individuals include Naim Audio started by Julian Vereker who designed their amplifiers, Nelson Pass who designs Pass Labs amplifiers, Bill Z Johnson who designed Audio Research’s valve (tube) amplifiers and Dave Wilson (and now Daryl) who designed Wilson Audio speakers.

This review is also about a one-man design team but what he designs is very rare, a designer of Digital Audio Converters (DACs). Those made by Chord Electronics.

By design I mean right back to the bare bones of a DAC. A lot, if not most DACs, are no more than a selection of an already designed DAC chip. The audio company builds the supporting circuit that brings the DAC to life. All the decisions about how the DAC process works have already been made by one of the main DAC chip builders such as ESS, AKM and Cirrus Logic. It should not be too much of a surprise to find a lot of DACs sound the same or very similar as the opportunity for individual companies to change the product is limited.

However, some companies do not do that and Chord Electronics is one of them. They should not be confused with Chord cables as they are separate companies. Chord Electronics’ DAC technology is designed by Rob Watts. Rob has a long and illustrious career in chip design for major chip manufacturers. He relates sad tales of the audio quality of these chips being very much second fiddle to the chip costs. He, therefore, enjoyed doing DAC design work for Chord electronics. Rob has been designing DAC chips for over 30 years and he is still refining them. Not only that but his approach to DAC design and his way of working is different from other designers. He listens and changes designs if it improves the sound quality of the audio. His approach to filter design, noise and measurements are also very different.

However, it is not a one-man show and praise should also go to John Franks and his engineers. They have consistently produced a high-quality audio product, which is solid, has great character and is superbly packaged. That takes some doing and they have mastered it. The fact it is done for £1195 and it is made in Kent at that price is some achievement.   

Rob Watt’s experience has shown him that there are three significant requirements for excellent sounding DACs. These are low noise floor modulation, excellent timing accuracy and small-signal accuracy. If those three are not done correctly then the audio will suffer and artefacts like a digital edge appears, accompanied by a flat and boring sound with little depth perception. I like his overall approach. If he hears a problem, he measures it, resolves it and then continues. He has been surprised many times about how sensitive human hearing is even when the measurements do not show a problem. Excellent design.

Picking on one issue, small-signal accuracy. Rob comments that if you go to a large hall with an organ and an orchestra in front of it, you get fantastic depth perception. The organ can be perceived even if it is 100m away. Now listen with an audio system and that huge depth perception, even with brilliant equipment, is significantly reduced and you may only be able to perceive the organ being 10m or 20m away. Why?  The small-signal accuracy of the DAC. Rob maintains other DACs are not very accurate with small signal accuracy. Small signal non-linearity is when the amplitude of a small signal varies from a larger signal. Rob uses Pulse Array DAC, a technique he invented some years ago. The Pulse array has noise-shapers that are claimed to be one billion times better at resolving small signals than conventional DACs, hence better depth perception.

 Of course, he has measurements to back that up.  You do not get to be a top chip designer without essential measurements.

However, the issue where he has spent a huge amount of time is with digital filters. According to the Shannon-Nyquist theory if an audio signal is frequency limited then all the information can be digitised by sampling at 2x the highest frequency needed.  The digital information then needs conversion back to analogue and filtered to remove the sampling frequencies, whilst leaving the audio data intact. These filters have had many years of study. They can reconstruct the original data perfectly if they follow a specific mathematical shape (sinc(x)). Unfortunately, that shape needs to have an infinite number of coefficients or ‘taps’ to perfectly reconstruct the audio.  Most DAC companies design DAC chips with just a few 10s of taps. But Rob Watts believes that is insufficient and a much larger number of taps are needed. To do that he has to write his computer code on, in effect, a blank computer chip. His DACs have a large Field Programmable Gate Array (FPGA) loaded with many thousands of lines of codes. These lines of code contain thousands of taps. The Qutest DAC has 49,000 taps.  The top DAC, the Dave, has 164,000 taps and there is an accessory box (M-Scaler) that has 1 million taps!! A lot of audio companies believe that a few 10s of taps are sufficient but Rob Watts and Chord Electronics do not.

There are many vids of his talks where he explains his approach in detail and I can recommend them, especially if you like measurements as he backs up all his comments with measurements.

Anyway, enough theory how about the Qutest.

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The Qutest comes in a very neat black box with two drawers with the DAC in one drawer and the accessories including the power supply in the other. The instructions are on a printed black, shiny, thick card. The instructions are well thought out and easy to read. The Qutest is a cuddly, small aluminium box which is machined from a solid billet of aluminium and then black anodised. On the front are two buttons that change colour depending on which filter you chose or which input you select. On the top of the box, there is a porthole that allows you to see inside the box and see the main processing chip (FPGA) with an acknowledgement to the designer Rob Watts. If you look through the porthole there are different coloured LEDs lit with their colour depending on the sampling rate that the DAC has locked onto. The Qutest processes the lot including high rate DSD; see the specifications for details.

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Round the back are the inputs/outputs including a USB, an optical input and 2xBNCs that support SPDIF. The two SPDIFs also support Chord Electronics' Dual Data protocol, so can accept/decode an upscaled 768kHz signal (16x that of CD) from the M Scaler, for example. The outputs are limited to 2 RCAs and it is therefore single-ended. And finally, a micro USB connection for the power supplied by a switched-mode power supply. The output can be changed to 1,2 or 3 V. and the Qutest has 4 different filter settings.  

I had no problem connecting the DAC and it locked onto all the sampling rates I sent from my dCS Bridge. I had to use a Melco digital library to provide the USB data as the dCS does not support USB.

So how does the Qutest sound?

I slotted the DAC in place of my AN DAC4.1x. So, I had my NAS drive feeding the Melco and PLiXiR PSU. They fed the digital signal into the dCS Bridge streamer and on to the Chord Electronics Qutest.  I used a variety of amplifiers with my AudioNote Es Signatures and their external crossovers. I started with my Cut Loose silver ribbon cables including a Cut Loose digital cable. 

The first amplifier was a Pass Labs XP22 and a Pass Labs XA 30.8. And a surprise. The little Qutest was really good, no I mean REALLY good.  

My biases were shattered.

I have heard Chord Electronics DACs at many shows and demos and the sound was always detailed, bright, aggressive and not very easy to listen to for anything beyond 15 minutes. That is not what I was hearing at home. It was detailed but very natural. There was a little bit of forwardness but no aggression or any sharp ‘digital’ sound. The soundstage was huge, layered and very 3D. Wow! I checked, it was a Chord Electronics DAC but it did not sound like what I was expecting or I had heard before.

OK, I switched to Qobuz and dialled up my new test list to see what this DAC could do with some more challenging music.

Leonard Cohen: You Want It Darker: This track starts with a choir of male voices. With the Qutest it was easy to hear the different tones of the singers, how they were laid out and the drama they were putting into the song, starting very quietly and building up until Mr Cohen starts singing/talking. Closely miked, he was close and intimate and different from the choir. As you go through the song you realise here was a man who knew he did not have a lot of time left on this mortal coil and was talking to his God and us.

Onto something a bit more cheerful, Wind of Change (MTV Unplugged) from the Scorpions with a favourite Norwegian guest singer; a live track in front of a large adoring audience. The contrast in voices, the rawness of a live recording, and a rock band was superbly rendered. The live feel of this track was easily heard with the instruments well separated but without much of a 3D soundstage, as you would expect from a live rock recording. There was a small edge to the sound but that could be the recording or possibly the DAC.

OK let’s try some bass. I played Flight of the Cosmic Hippo by Bela Flack with Victor Wootan on bass guitar; Jennifer Warnes, Way Down Deep and Coldplay: Everyday Life, Trouble in Town. On all of the tracks, the bass was tight and it was easy to hear the tone of the bass instruments (synthesised or otherwise) and dare I say it, follow the tune. Fast bass was fast bass, not fat bass.

As well as all these audiophile tunes, I tried some AC/DC. It’s a Long Way to the Top (If You Want to Rock ‘N’ Roll) starts with some raw guitars and then it picks up with another guitar and the bass. And then of all things some bagpipes. Yes, bagpipes on a rock track! This less than audiophile track tests whether the system can rock with some raw music and the bagpipes can turn into a screeching mess with highly detailed forward DACs. Not here. Nice, it was not, but screeching it did not.

This was turning out to be real fun.

I then wheeled in the big comparo, the Audionote DAC2.1. This box of tricks has had a few super-duper signal tubes added. So far, I have taken this DAC to many bake-offs, used it as a reference point for reviews and it has never been seen off by any other DAC. Yes, certain aspects in other DACs were better but not to the extent that I would seriously question its music-making abilities. So off I went with my music lists using a real mixture of music including the real decider, the live recording from St Martins in the Field of Beethoven’s Fifth Piano Concerto recorded by Mike Valentine (and yes, I was there).

And these two DACs highlighted the current differences in good DAC design. The Audionote was very musical and had the real heart of the music but was a little soft in transients, drums had less ‘crack’, the image was a little soft focus and it was not always easy to identify all the words the singer was singing. The Qutest was detailed, natural, very atmospheric with great 3D imaging. It showed the detail in the singer’s voices but did not quite capture the emotion as well as the Audionote. The Qutest was more honest and truthful with less than good recordings. No, it did not go into digitalis but it did not cover its tracks as well. So, one was an accurate transcription of the music whilst the other had lightly tinted glasses. I could easily imagine people hearing either and preferring one over the other.

For me, the Qutest had it. It had just so much extra detail that was musically important and integrated. It worked better with the Pass Labs. Never thought I would say that after all these years.

When I used the Allnic Integrated with its KT150 valves my preference moved more towards the Audionote but not by enough to displace the Qutest. With the Allegri passive/Nord 500 Class D the Qutest had the better sound quality as the DAC and amplifier complemented each other. (Never got a chance with the 211 Transcription amps due to the mini heatwave).

And the AN DAC4.1X? Come on guys. That combined the best of both the AN 2.1X and the Qutest and then added greater realism. But let’s not decry the Qutest as the AN DAC 4.1x is close to £14K.

I managed to squeeze a bit more from the Qutest by isolating it more effectively with footers so you need to take care with its positioning. And cables made a difference but that needs another review. Coming soon.  

In conclusion, colour me surprised, shocked even that this little lovely looking box has a sound quality well above most DACs at its small price of £1195 and certainly a lot of others that cost more, much more. It seriously challenged (and beat) my reference which has seen off a large number of other DACs and is itself more than twice the price of the Qutest.   I preferred the Qutest to my reference AN DAC2.1X. The King has lost its crown.

And there are rumours that it is possible/desirable/essential to change the Switched Mode Power Supply and then the Qutest can show what it can do. And there are many Linear PSUs out there to try……so I…….did… NOT. I promised Chord Electronics I would not do this and as it is not my product, I did not try it out.

Their official view is: The problem is audiophile linear PSUs have no RF filters at all; the designers are not cognisant of the RF noise problems. The supplied Chord Electronics PSU, on the other hand, has RF filters built into the output and the mains input. So, if connecting a linear PSU, it will most likely sound worse due to the increased RF noise, but the extra brightness can deceive the listener into thinking it is ‘better’. Note: using anything other than the supplied Chord Electronics PSU will also invalidate any warranty.

But many have tried using high-quality linear PSUs including my audio buddy Martin V using his Chord Electronics Qutest and an SBooster PSU + extras. His review follows. And you will be interested in what he found.

Over to Martin V.

Specifications

Materials: Precision machined aluminium casing with polycarbonate buttons and glass viewing portal. Available only in Jett Black.

Device power supply: 5v 2amp Micro USB

Tap length filter: 49,152 – 10 element Pulse Array design

Connectivity (input): USB Type B (White): 44.1kHz to 768kHz – 16bit to 32bit

2x BNC Coax (Red): 44.1kHz – 384kHz – 16bit to 32bit

1x Dual data mode input (using both BNC coax inputs together): 44.1kHz to 768kHz – 16bit to 32bit

Optical (Green): 44.1kHz to 96kHz – 16bit to 24bit

Connectivity (output): 1x stereo pair of RCA (Left and Right)

PCM support: 44.1kHz, 48kHz, 88.2kHz, 96kHz, 176.4kHz, 192kHz, 358.8kHz, 384kHz, 717.6kHz, and 768kHz.

DSD support: Native playback supported. DSD64 (Single) to DSD512 (Octa-DSD)

Variable output: Fixed, but selectable between 3v (blue), 2v (green), and 1v (red) via dual press of ‘Filter’ + ‘Input’ upon startup

Digital designer: Rob Watts

Mechanical designer: John Franks

Country of manufacture: England

Chipset: Chord Electronics custom coded Xilinx Artix 7 (XC7A15T) FPGA

Tap-length: 49,152

Pulse array: 10 element pulse array design

Frequency response: 20Hz – 20kHz +/- 0.2dB

Output stage: Class A

THD: <0.0001% 1kHz 3v RMS 300Ω

THD and noise at 3v RMS: 117dB at 1kHz 300ohms ‘A’ weighted (reference 2.5v)

Noise 2.6 uV ‘A’ weighted: No measurable noise floor modulation

Channel separation: 138dB at 1kHz 300Ω

Weight: 770g

Dimensions: 4.5cm (H) 16cm (W) 8.8cm (D)

Boxed Weight: 1500g

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