Chord Dac 64 - Chord Electronics

Retro
Retro
Out of this world
David Price tells the stellar story of one of the world’s most innovative
DACs thus far designed, Chord Electronics’ DAC64
O
ne of the finest-sounding
digital-to-analogue
converters ever made
was born after a chance
meeting that is the dictionary
definition of happenstance. The story
starts when our key protagonists meet
at the Las Vegas Consumer Electronics
Show in the early nineties. The first
is Rob Watts, the digital electronics
whizkid who gave the world some of
the finest-sounding DACs of the early
nineties when he was designing for
his company, Deltec Precision Audio.
The second is John Franks of Chord
Electronics, a company that was
beginning to make inroads into the
hi-fi world.
A casual conversation turned into
something that created the DAC64,
and no, it wasn’t about hi-fi! Rob
takes up the story: “DPA and Chord
shared the same US distributor, and
I met John in Vegas one year. We
started chatting, and I asked him
where Chord were based. He said
‘Maidstone’. ‘Oh, that’s interesting’,
I replied, ‘because my parents have
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just bought a house in Maidstone’.
John asked whereabouts and I
replied, ‘a place in Allington”. ‘That’s
interesting,’ he says, ‘I have just
sold a house there’.” And yes, you’ve
guessed it, Rob’s parents had just
bought John’s house! “We were
fated to work together”, he adds.
This led Rob to demonstrate his
own Pulse Array DAC technology
using Field Programmable Gate
It remains one of
the nicest digital
converters to listen
to and to look at
Arrays to John. Rob was already
making a name for himself in the
wider hi-fi world by then.
At this time, the mainstream CD
player market – which was now
booming – was dominated by
variations on the theme of Philips’
newish Bitstream technology. CD
player makers either bought the
SAA7350 chips off the shelf, or
stuffed the older ones such as Philips
TDA1541s in. But Rob was doing
something radically different,
wanting to completely remake
the DAC and digital filter in
reprogrammable memory chips that
he could code himself. At the time,
only dCS was doing anything like
this; everyone else was buying in
someone else’s chip and then putting
it in a fancy box.
“Around that time, the capabilities
of FPGAs started to get very serious”,
remembers Rob. “I realised that I
could do the interpolation filter
function as well as the DAC. Ever
since the early eighties, when I
studied electronics at university, I
realised that the interpolation filters
in use then and today, were
fundamentally limited and had severe
timing problems. This was based
on studying sampling theory, which
clearly states that to perfectly
reproduce a sampled bandwidth
limited signal you need an infinite tap
length filter. Using conventional filters
(about 100 taps max.) would have
severe timing problems. I also knew,
by studying hearing, that the ear/
brain could resolve 4µs of timing,
but CD is only accurate to 22µs –
the missing timing is reconstructed
by the interpolation filter.”
Rob put this idea to John and
after “a lot of time and effort”, he
demonstrated the prototype DAC64
complete with the first 1k tap Watts
Transient Aligned filter, “and it
knocked our socks off”. Rob did all
the electronics, and Chord duly
encased it in one of the company’s
gorgeous aluminium housings.
It wasn’t just Rob’s unique,
custom-made digital filter that made
it sound the way it did, though.
Another other key aspect was the
buffer, which meant that Rob “could
hear a jitter-free source, so this was a
big advantage. Today, I have digital
phase lock loops DPLL that matches
the sound of buffers, which is great
as buffers can’t be used with video.
Without the DAC64 buffer, it would
not have led to the DPLL
development, which has solved
other problems too”, Rob adds.
When I’m 64
Finally, as its name suggests, the new
Chord DAC sported ground-breaking
64-bit architecture. This was
remarkable in its day, especially when
you consider that 15 years later
we were only beginning to see the
ubiquity of 32-bit DAC chips from
the likes of ESS, for example. Rob
takes up the story: “This core was
as a result of being worried about
coefficient truncation issues, signal
truncation, and other problems.
So the best solution was to use a
sledgehammer and run with 64-bits
as I had plenty of gate capacity.
Today, I have completely solved the
truncation issues, by employing dither
and noise shaping techniques, and
the multiple DSP cores are now
48-bit. But today I am working
with much more parallel cores
at much higher speeds.”
Lesser companies might have been
content to dump Rob’s brilliant,
bespoke circuitry in a black box,
possibly with an extra thick slice of
brushed aluminium for a fascia, for
good measure, but not Chord. Rather,
the aesthetics of the DAC64 were
almost as radical as its electronics.
The 7kg casing felt like a hollowed
out billet of aluminium, and an
inspired touch was the top-mounted
‘magnifying lens’ that showed off the
electronic crown jewels – so to speak
– inside. But the internal illumination
didn’t just flood the circuitboard
with light, it also provided status
indication. At switch on it was blue,
and when locked onto a digital signal
red LEDs lit up to give a purple hue.
Yellow LEDs lit to show that either
of the RAM buffers were switched in.
It was about as tactile and visually
interesting as you could make a DAC.
Round the back, there was a choice
of Toslink optical, coaxial S/PDIF via
a BNC jack, and AES/EBU via XLR –
all selected by a toggle switch.
Another toggled between the two
RAM buffer settings, and there was a
choice between balanced XLR and
RCA phono audio outputs. Designed
at the turn of the millennium, no USB
input was fitted, but it was able to
accept a 24/96 signal via its coaxial
input – ideal for the DVD players of
the day. It wasn’t capable of the full
64-bits that its name alluded to;
rather it referred to the 64-bit DSP
core used to do number crunching –
the seventh-order noise-shaping for
the Pulse Array DAC was done with
64-bit precision. Inside, you can see
the Xilinx FPGA chips that do the
maths, and because it was pretty
high-powered stuff back then, the
unit runs surprisingly hot.
Any fan of high-end digital back in
2002 would have been amazed to
hear the DAC64. Fed by a serious
high-end CD transport, and goodquality coaxial digital interconnect
and given an hour or so to warm
through, the results were startling. In
the pre-DAC64 world, there was only
a handful of high-end designs that
gave anything close to an analogue
sound. Most were stark, mechanicalsounding devices that resolved detail
well and impressed with their power
and punch, but few were able to
provide a rounded, smooth, open and
natural sound – something that vinyl,
Dac’s entertainment
The DAC64 was one of the most exciting
moments in Rob Watts’ career he tells me,
but right now he is rediscovering the feeling
with his latest DAC design, the Chord Hugo.
This is no less innovative than the DAC64,
and is basically a refinement of all the
technologies he brought to market with it,
adding more interesting and bold ideas. “I
am very, very, excited about Hugo. This is the
result of six years of digital design work,
looking at lots of key aspects, lots of listening
and new developments,” he tells me.
”I believe it is more groundbreaking than
the DAC64 was. The reason is that the
Hugo has changed my appetite for music.
I am listening much more now, and get
far more pleasure from music with Hugo.
The change in musicality was completely
unexpected. I knew it was going to be
better than the Qute DAC, but it was
devastatingly better, and in ways I had not
expected. Not only that, I knew the sound
of the individual parts before it was all put
together – but it is performing much more
than the sum of all the improvements I’d
put into it. Indeed, this still puzzles me!”
Watch out for a full review of the new
Hugo in next month’s issue.
John Franks
introduces his
latest: Hugo
despite its other faults, does very well.
The new Chord DAC was different.
Tonally it was smoother than most,
almost as if there was a slight roll off
in the higher frequencies, although
you’d never call it dull. At the same
time, the bass was warm. Across the
midband, it was expansive, spacious
and above all natural, so the result
was a sound that had all the
superficial appeal of analogue. But
more than this, it timed brilliantly.
The 64 was able to piece together the
musical information in a way that
made rivals sound frigid, as if they
were playing by rote, robotically
recreating the sound without passion.
The Chord on the other hand served
up beautifully syncopated music, with
all the rhythmic snap and dynamic
drama of a live performance.
Somehow, it just didn’t sound
processed, as others did – and still do.
The combination of this lovely,
fulsome tonality allied to its ability to
faithfully render the natural rhythm
of the music in all its glory, made for a
unique listening experience. It simply
didn’t sound like anything else.
The legend lives on
In today’s digital world, it lacks a little
inner detail and is disadvantaged by
its lack of USB connectivity and
24/192 functionality. Yet it remains
one of the nicest digital converters
to listen to and to look at, and that’s
why it’s become a legend. Every now
and then, you’ll see one for sale
secondhand for around £800.
Meanwhile, Chord Electronics’
modern DACs continue to wow us l
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