Best Buys Audio & AV 2019-#279
keep!) This VU meter shows the level of the
incoming signal, rather than the level going to the
headphones, which is what you might expect.
The DAC Stax is using inside the SRM-D50
to convert digital signals to analogue is one of
ESS’s earlier-generation DACs (ES9018) but it can
handle all 16-bit or 24-bit PCM file formats up to
384kHz as well as DSD 2.8/5.6MHz (using DoP),
and its performance is excellent, as it uses ESS’s
patented 32-bit Hyperstream DAC architecture
and Time Domain Jitter Eliminator, which ESS
claims delivers a signal-to-noise ratio of 135dB
and THD+N of just 0.0001%. It also has a filter
that can be programmed for any type of roll-off,
though Stax doesn’t give any indication of what
type of filter it is using.
Given the high quality of the DAC and the
dual JFET operational amplifier which follows it,
it’s perhaps a surprise that Stax has not fitted a
line output to the SRM-D50 to enable owners
to use it both as a headphone DAC and as a
conventional DAC. This would have been a great
‘value-add’ as without this, the box becomes a
‘dead-end’ for inputs, when many might like to
chain it through to their main hi-fi when
not listening to headphones.
To evaluate the SRM-D50, Stax’s Australian
distributor Audio Marketing also loaned us
the latest SR-L500 earspeakers, new in their
MkII status, with detachable cables and head-
band upgraded to aluminium. You could,
however, use the SRM-D50 to drive any
‘PRO-Bias’ Stax earspeakers.
The SR-L500 design has fixed perforated
stainless steel electrodes between which is a high-
polymer 45×90mm thin-film diaphragm that’s less
than two microns thick. The four stainless steel
electrodes (two per ear-piece) mean that these Stax
SR-L500s are rather weighty on the head, tipping
the scales at close to half a kilo. Thankfully,
the headband has been made wide enough and
comfortable enough to distribute
this weight over a larger surface area of your
head, so the weight isn’t as noticeable as it might
otherwise have been. There’s plenty of room for
even the largest ears to fit inside the rectangular
enclosures, which also means that the sound is
arriving at the ear from above and below the
external ear (pinna), which gives a more natural
sound than if the sound waves are only fired
directly into the ear canal, as happens with
conventional dynamic drivers whether they’re
around-ear, on-ear or in-ear types.
The headphone cable is also completely
different from that of conventional dynamic
drivers, due to the need for the additional
electrical conductors required to provide the bias
voltage to the electrodes. The six cables are arrayed
alongside each other in a flat configuration in
order to reduce the capacitance between them, so
the cord looks for all the world like a long strip of
liquorice in terms of shape, colour, even texture!
The conductors inside the cable are made from
high-purity copper purified to 99.99999%-pure
using a technique patented by Hitachi.
PERFORMANCE
The purity of the
sound issuing from the
SRM-D50/SR-L500 MkII
combo was simply jaw-
dropping, and at times
we were literally open-mouthed in
wonderment. The reproduction of the
sound of the flapamba that introduces
Rikki Don’t Lose That Number, from
Steely Dan’s ‘Pretzel Logic’, is absolutely
perfect. If you listen to this track on
ordinary headphones (or loudspeakers)
you’d be forgiven for thinking you were
hearing a marimba, but if you listen
using this Stax combo, you’ll immediately
know it’s not a marimba at all, but
some other similar-sounding percussion
instrument (even if you’ve never heard
the sound of a flapamba).
It isn’t only the tonal nature of the
flapamba’s sound, but the spatial quality
of it, where the sound starts high up and
to the left, then partially pans down and
across for a brief foray to the right, all
the while not quite maintaining focus,
before returning right and disappearing
totally... which means that when the
piano riff (famous, but actually knocked
off from jazz composer and pianist
Horace Silver’s Song For My Father) kicks
in totally focused at stage centre, the
dramatic effect is stunning.
The clarity and ‘open-ness’ of the
sound from the SRM-D50/SR-L500
combo is so amazing that it’s easily
possible to completely forget you’re
wearing headphones, so complete is the
illusion of space and depth. The ‘sound from
the centre of your head’ feeling that you often
get when listening to headphones, particularly
when there’s a strong central stage presence, was
completely absent. A part of this is no doubt
due to the design, because sound is issuing from
both sides of the diaphragm, so anyone in the
same room as you is going to hear a rather tinny,
low-volume version of whatever you’re listening to.
Given the lack of distortion and the spatial
clarity of the Stax SRM-D50/SR-L500 you might
well imagine that they’d be perfect for listening to
complex full-scale orchestral works... and you’d
be perfectly right: they are ideal for this purpose.
But in fact the Stax SRM-D50/SR-L500 combo
will deliver the sound of any musical genre to an
exceptionally high standard... the very highest
standard, in fact.CONCLUSION
So it does seem to be true — once you have
listened to your favourite music through a pair of
electrostatic headphones — sorry... earspeakers!
— you will be spoiled for anything else. And by
integrating DACs into its drivers, Stax is making it
ever-easier and ever-more convenient to make the
switch to electrostatic listening.Stax SRM-D50 Driver/DAC &
SR-L500 MkII Earspeakers- Sound quality!
- No line output
- Single output only
Stax SR-L500 MkII earspeakers
Price: $1200
Type: Push-pull open-back oval electrostatic
Frequency response: 7Hz–41kHz
Impedance: 145kΩ inc. cable, at 10kHz
Sensitivity @ 1kHz: 101dBSPL/100VRMS
Maximum SPL: 118dB/400Hz
Bias Voltage: 580V DC
Weight: 479g (inc. cable)Stax SRM-D50 Driver/DAC
Price: $2100
Inputs: 1 x RCA analogue, 1 x USB-B,
1× optical, 1 × coaxial
Gain: 59dB
THD: >0.025%
Input impedance: 20kΩ (RCA)
Bias voltage: 580V DC
Dimensions (whd): 192 × 67 × 268mm
Weight: 4.5kgContact: Audio Marketing Pty Ltd
Telephone: 02 9882 3877
Website: http://www.audiomarketing.com.au“The purity of the sound was simply
jaw-dropping, and at times we were
literally open-mouthed in wonderment.”