model 901 in Pro Audio Review by Tom Jung - Grace Design

The Industry’s Equipment AuthorityREPRINTED FROM SEPTEMBER 2002WWW.PROAUDIOREVIEW.COMGrace Design 901Headphone Amplifierby Tom JungGrace Design has earned a reputationfor quality products over the pastfew years with a line of high-endmicrophone preamplifiers. Ireviewed the 801 eight-channel preamplifierin the March/April 1996 issue of PAR andhave since used it on many projects.Michael Grace has come up with a headphoneamplifier employing the same passionfor quality as he has for his microphonepreamp designs.FeaturesThe 901 has the same quality look and feelof the Grace mic preamps, complete with aprecision gold contact 24-position level controlswitch. Most headphone amplifiers usedual gang potentiometers with tracking errorsof several dB, especially at lower gain settings.Interchannel tracking error can be areal problem affecting both stereo image andinternal balances with the potential of throwingoff a mix. With the 901 precision attenuator,channel-to-channel accuracy is maintainedwithin 1/20th of a dB at all gain settings!Try that with a pot.The 901 has both balanced XLR andunbalanced RCA analog inputs as well asPCM digital inputs in both AES/EBU andS/PDIF formats, the latter available in RCAand TOSlink optical. A back panel miniaturetoggle switch selects between the pro andconsumer formats.The front panel has two centered 1/4-inchstereo headphone jacks wired in parallel anda large power switch to starboard, gain rangecontrol to the left. The digital/analog pushbuttonsare sealed gold contact relays and areilluminated. Nice. A low distortion 24-bitDAC accepts sample rates up to 96 kHz withfour LEDs indicating from 32kHz to 96 kHz. The DAC also employs anautomatic digital de-emphasis filter.Like the Grace mic preamps, the levelFast FactsApplications:StudioKey Features:24-position gain control;onboard D/A converter; 96kHz performance; XLR, RCAinputs; digital inputs; consumerand pro operationPrice:$1,495Contact:Grace Design at 303-443-7454, www.gracedesign.com.control is adjusted with a custom knobmachined out of solid aluminum and isshaped so that from across the room you cantell by the angle of the knob where the gain isset. The 24-position gain control is just right,making it easy to get back precisely to yourreference settings while providing justenough resolution. In addition, the taper layoutis well thought out. Here is the breakdownof level control taper: fully counterclockwiseis off, the next two steps go from–60 to –50, the next four steps are 4 dB eachand the remaining to full up are in 2 dB steps.Perfect. The Gain Range switch provides anextra 10 dB of gain for monitoring –10 dBVor consumer level signals. This is also usefulfor low sensitivity headphones.The 3 dB down points for frequencyresponse are at 4 Hz and 600 kHz . Of coursethis is in the analog mode, which is where Igenerally listen to the 901. You can be sureDSD signals are not going to be compromisedby this kind of bandwidth.Copyright 2002 IMAS Publishing (USA), Inc. Reprinted with permission.

In UseThe 901 uses a high-current output amplifierwith an output impedance of 1 ohm andis capable of driving 8 ohm loads. Perhapsbecause of its low output impedance, the 901has the best low-frequency control of anyheadphone amp I have heard. Most headphoneamplifiers have output impedances of100 ohms or more, making them potentiallymore bulletproof at the expense of low-frequencycontrol.The internal high-current linear power supplyuses a high-current, low-noise, toroidalpower transformer, giving the 901 just enoughweight so that when you plug and unplugyour headphones you do not have to hold onto the amplifier with your other hand.The signal path is about as pure as youcan get using high-grade instrumentationinput amplifiers, high-quality metal filmresistors and no electrolytic capacitors in thesignal path.I really liked the sound of the Grace 901.About five seconds after I plugged in myGrado HP-1 reference headphones (PAR9/96) I knew this amp was going to takethese phones to places they had never beenbefore sonically. The first and most obviousarea was the low end. Much of my workincludes acoustic bass, which is traditionallydifficult to reproduce accurately, especiallywith headphones. This is the one area wherereference monitoring on headphones fallsapart due to the fact that most amplifiers donot have good control of the headphonedrivers, causing low-end boom. This boomcreates a masking effect that clouds theentire bottom end, making it difficult to mixor make tonal adjustments in those low-frequencyareas. The 901 has the best bottomendcontrol I have heard. It also seems likemy Grado headphones have another octaveof bass extension.Good bass is not all; the top end has opennessand extension as well with incredible harmonicdetail and air. With a DSD signal connectedto the analog inputs, the depth andwidth of the soundstage was about as good asI have heard on headphones. The PCM inputsare very good as well, with proper analog circuitryfollowing the DAC chip. This makes the901 an excellent D-to-A reference monitoringdevice. The Grado headphones are about 40ohms and are fairly easy to drive, but the 901has plenty of power and can drive much lowerimpedances and more difficult loads.SummaryI know of no other headphone amplifierthat performs as well as the Grace 901. At$1,495 the 901 is not cheap, but this kind ofexcellence represents a good investment ifyou really care about audio quality.Tom Jung, founder of DMP Records, isPro Audio Review’s technical consultant anda regular contributor.REVIEW SETUPPhilips SACD-10 PE CD player; EMMLabs DAC8 D/A converter.Product PointsGrace Design 901Headphone AmplifierPlus• High-end performance• Quality construction• Useful I/O choicesMinus• PriceThe ScoreI know of no other headphoneamplifier that performs as wellas the Grace 901.Copyright 2002 IMAS Publishing (USA), Inc. Reprinted with permission.Reprinted from Pro Audio Review