Grace Design Model 901
Reference Headphone Amplifier Review
ã 2002 By Eddie Ciletti
"Eliminating the Weakest Link"
There are times when only Headphones can reveal the fine detail and
nuance that engineers need when choosing preamps and microphones, listening
for background noises or doing quality control. That’s why the Grace
Design Model 901 Reference Headphone Amplifier is the answer, the type
of product my hardcore customers would buy in a heartbeat and I totally
get it. By eliminating an often overlooked weak link in the chain (see
the Sidebar "Bench Perspective"), the Model 901 encourages critical
listeners to match the quality of this device with better than average
This is the first Grace Design
I have ever reviewed. Its 1-RU height and half-rack width is deceptive
because at five-plus pounds, at first I suspected that a dummy weight had
been added to make the unit "feel" more substantial (and to keep it from
sliding around). I couldn’t have been more wrong. The Model 901’s considerable
"heft" is due to its thick steel chassis, toroidal transformer (no wall-wart,
yeah!!) and quarter-inch thick aluminum front panel construction. Inside,
the build quality and components are top notch.
As a converter alone, the Grace 901 can justify its $1495 List Price
because the foundation is high quality 24-bit / 96kHz Digital to Analog
conversion interfaced to the outside world via rear panel AES, SPDIF and
Toslink connectors. Most equipment does not have conversion of this quality
both in terms of components and execution, plus th converter sub-assembly
can be upgraded to a higher sample-rate module if and when it becomes available.
A front panel switch chooses between the Digital or Analog inputs (XLR
or RCA), the Level Control is a rotary switch with precision resistors
— to ensure long trouble-free life and channel-to-channel stability — followed
by a high quality, high power output amplifier. A front panel "Range" switch
ensures that the Model 901 can drive any impedance headphones via the two
front panel jacks. The unit could probably drive a pair of speakers though
I didn’t try that! It is recommended that the analog input of the Model
901 be driven from a low-impedance source (typically 100-ohms or less,
1k-ohms is too high).
THE CRITICAL LISTEN
Over the years, when customers with critical ears discussed headphones,
a few names have been repeated over and over. On the short list that also
includes Grado, Stax and Sony, I acquired a pair of Sennheiser HD600 headphones
to make this marriage complete. The first "test" was a Jazz Trio consisting
of Acoustic Bass, Drums and Piano in a live recording space with no control
room. (Click this Jazz
Link for full session details plus an mp3 sample.)
During the recording I worked exclusively in the headphones and it was
heavenly as there was no isolated control area. On playbacks we listened
on ProAc Studio 100 monitors while the headphones were passed around.
The session was recorded to a Fostex DV-40 4-channel DVD- RAM recorder.
Two channels came direct from the board plus another pair from an Audio
Technica Stereo Shotgun mic in the balcony — using either an AT815ST or
an AT835ST. From the Fostex, the main mix pair was digitally connected
to the Grace 901 while the shotgun pair was fed via analog connection.
After the session, The Grace 901 was connected to a Z-Systems digital detangler
using either an Alesis Masterlink (at 88.2kHz /24-bit) or a Technics CD
player as sound source.
Sony V-6 (7506)
TABLE-1: List of headphones tested with the Grace Model 901 Reference
Headphone Amplifier. (The spaces between the rows group the headphones
into similar sonic categories.) H and L refer to the Range Switch (for
high- and low gain) which more often than not corresponds with the level
required to drive high- and low-impedance headphones, respectively.
Table-1 is the list of headphones tested along with the Model
901 Headphone Amp. At left the list is in descending order of personal
preference, the spaces between the rows group the headphones into similar
sonic categories. The level settings are "clock-wise" and quite relative
although very in the ballpark in terms of Impedance. The "H" and "L" refer
to the Model 901’s "Range" switch, High and Low Gain optimizes the level
for high and low-impedance cans.
What is so impressive about the Grace Model 901 is the silence; there’s
not a hint of hiss, extraneous noise or hum. When partnered with the Sennheiser
HD-600 (about $299 "street"), the sound is open, effortless, extended and
spacious. The top is delicate and the bottom full. Nearly everyone knows
what the Sony cans sound like — not as nice as the HD-600 — but not so
far away as some of the other headphones on the list and about one-third
the street price. Considering the Impedance difference (300-ohms and 0-ohms),
the Model 901 had no difficulty driving either pair. For more info on the
headphone test, see the SIDEBAR: Can-Can.
Taking the time to audition various headphones, source material and
the Grace Model 901 Reference Headphone amplifier is an exercise I recommend
to everyone. Those who rely heavily on headphones have most likely done
the research enough to know the value of this product in the Classical
and Jazz environments. For everyone else, I highly recommend the Grace
901, especially when sonic comparisons make it difficult to distinguish
whether the gear or the source material is at fault.
Auditioning multiple headphones (listed in Table-1)
was a revelation if only because time is rarely taken except at the time
of purchase. I’ve used the Sony V-6 cans for years, they are also known
as the MDR-V7506, perhaps the most popular because of their price / performance
ratio. In between, the Sennheiser HD-280 pro cans are designed for isolation,
sonically similar to the Sony with perhaps a bit more bottom. The Fostex
T20 cans are warm and comfy, their midrange smooth but with significantly
less top. They are a similar vintage to the AKG-240 cans, which have less
low end and more top than the Fostex, not extended like the V6 and more
like the AT D40fs. Like the HD-280, the ATM40fs cans are designed for isolation
and level. Unlike the D40fs, the top end is almost odd and not nearly as
nice as the D40fs.
Whether listening with headphones or loudspeakers, the ear’s Loudness
Curve is quite the moving target. ( For
more info on the topic of Bass Management, click here .)
Just from this listening test I noticed how different a headphone’s midrange
can seem based on what the ear perceives as "louder." For example,
at the top of the list, the Sennheiser HD600 cans have such "extended"
top and bottom that their midrange never seems painful even when cranked
up. At the bottom of the chart, the more mid-rangey cans seemed capable
of more "pain" in that region because the lack of top and bottom made them
seem less loud than they actually were. A headphone’s spectral response
above 4kHz also effects the imaging quality substantially.