Review:

Currently they sell amplifiers only, although from talking with them, they may branch out into other areas in the future. The subject of this review is the 7 channel Blue Diamond series amplifier. The Blue Diamond is rated to deliver 200 watts per channel ( with all channels being driven simultaneously ) into 8 ohm speaker loads, and 400 watts per channel into 4 ohm loads. It features gold plated speaker binding posts, unbalanced RCA line level inputs, balanced XLR inputs, a 12 volt DC trigger assembly and a grounded IEC power input. Gemstone makes a 5 channel version which is identical. The 7 channel Blue Diamond and the 5 channel Blue Diamond retail for $2499 and $1999 respectively and come with a 5 year warranty.

The Blue Diamond arrived at my door packaged well from Gemstone. It’s funny but I never seem to get used to just how incredibly heavy amps like the Blue Diamond can be. This is one beast of an amp weighing in at 90 plus pounds. Upon removing it from it’s carton I was impressed with it’s build quality and looks. The front panel is made of black brushed aluminum with the Gemstone Audio logo spotted centrally above a rounded blue power LED and a single power button.



The sides are adorned with large aluminum fins which run the length of the chassis. I assume that these help to dissipate any heat build up. Around the back there are 7 rows of gold plated speaker binding posts which accept banana plugs, spade lugs, or bare wire.



There are both RCA line level inputs and XLR inputs, numbered 1 through 7, as well as a 12 volt DC trigger input for automatic turn on via a corresponding output on a pre/pro. Lastly the IEC power cord input is centrally located near the units bottom on the back panel. Over all the I found the back panel to be uncluttered and well laid out.

I connected the Blue Diamond to my B&K Reference 50 A/V Controller via the RCA inputs. I also made use of the 12 volt DC trigger to allow the amp to be turned on when I powered up the Reference 50. Once all the connections were made I powered things up. I noticed that there was a low level hum coming through the three front channels, and the two rear center surround channels. There are no ground loop problems in my room so I decided to try connecting the Gemstone to my Reference 50 via it’s XLR inputs. Upon doing so and powering up, the hum was gone. The unit ran dead quiet in all channels. I calibrated the setup via my trusty Radio Shack SPL meter and jumped in for a quick listen to some two channel music. I popped Nora Jones’ Come away with me SACD into my Denon 2900 universal player. I almost always listen to this disc in stereo as I feel it has more depth than the surround sound version. I was immediately floored by the Gemstone’s airy and detailed presence on Nora’s vocals. I have never heard this recording sound so good. I noticed layers within it that were obviously there but never brought this close to the surface. I was intrigued and decided to go a bit further. I listened to Diana Krall’s WhenI look in your eyes SACD next. This is one of my favorite DK discs and a staple for two channel demo. “Let’s face the music and dance” was superbly rendered, with no hint of grain, and a richness which seemed to give it more room to breath. At this point I stopped any further critical listening and broke the Gemstone in for 70 hours. I was really curious to see if the Blue Diamond’s sound would change after a brief break in period. I once again listened to the two aforementioned SACD’s to see if I could detect any differences in the sound of the amp. Once again all I heard was sound that was totally relaxed yet completely controlled. The Gemstone did not get in the way of the music but let it come through. I had heard hints during the DK and NJ SACD’s of what appeared to be strong low end impact from the Gemstone. I wanted to see just what it could do with a recording that had some low end kick. The Yellow Jackets “Blue Hats” is one of my favorite progressive jazz recordings. Bassist Jimmy Haslip’s 6 and 7 string fretless MTD basses can supercharge the room with an amp which is willing to keep up. The Gemstone did not disappoint on tracks like “With these hands” and “Coal Minor Blues”. The Blue Diamond had excellent bass control which revealed itself where appropriate. Bass was tight, powerful, and had a richness that flowed into the room rather than boomed it’s way in. The Blue Diamond reminded me of the Outlaw Model 770 in that it had similar qualities in bass response. The Gemstone however exercised a bit more restraint in the mid bass where appropriate and reached down deeper when called upon. The same was true with classical recordings. Jerry Goldsmith’s “The Generals” from his SACD of The film music of Jerry Goldsmith was truly awesome. This multi-channel SACD when played to higher sound pressure levels can bring lesser amps to their knees. The Gemstone never broke a sweat and deliver the goods with dynamics, clarity, and total control. I felt that this amp really performed extremely well with music, especially with female vocals. This is an area where some amps tend to run into trouble. This trouble can be described as harshness, noticeable treble grain, and reticence. The Blue Diamond did not suffer from any of these and in fact rendered symbols, brass, and acoustic guitar with smoothness and textures which never became fatiguing. I would have to say that the Gemstone Blue Diamond was the most musical amp I have auditioned.

After my experience with the Gemstone’s musical chops I was pretty certain that it would have no trouble satisfying my home theater expectations. Right off of the bat I set my 7 channel Paradigm speaker suite for full range without the subwoofer. I wanted to see not only if the Blue Diamond could handle supplying the deep bass associated with digital movie soundtracks but all of the nuances that go along with bringing a soundtrack to life. I started things off with Tears of the Sun starring Bruce Willis. This films contains some excellent surround sound material. Early in the film there is a scene where Bruce, his group of commandos, and about 40 refugees are attempting to evade a group of Military in the jungle. This scene contains a wide variety of subtle sounds from heavy breathing, background animal sounds, the voices of the oncoming Military, to the click of the safety on an assault rifle. The Gemstone conveyed these details with clarity and definition. During the explosive climax the Blue Diamond opened things up quite nicely. As planes flew overhead, rocket propelled grenades exploded, and assault rifles unleashed their fury, the Gemstone pulled you into that jungle. It delivered superb dynamics, room shaking bass and plenty of headroom to spare even at extreme sound pressure levels. Moving on to the Lord of the Rings, The Return of the King DVD yielded similar results during the huge battle sequence near the City of Gondor. The Gemstone kept it’s composure as swords clashed, hooves drove hard into the ground, boulders smashed into buildings, and the Nasghoul circled overhead. Subtle details could heard while explosive bass transients thundered through the soundstage. Dialog remained crystal clear and intelligible throughout. Reinserting my subwoofer into the equation only made the Blue Diamond better. With the sub handling the LFE the Gemstone didn’t breath a sigh of relief but decided to open up a bit more. I detected a bit more of an open sonic presentation with maybe a tad more detail. This is not to suggest that the Blue Diamond needs any help, however I think it enjoyed the freedom all the more. The Gemstone never became anything more than slightly warm to the touch even under continuous operation at high volume levels.

Conclusion:

Evaluation system:

• Number of Channels 5 or 7 channels
• Mode of Operation Class A/AB
• True Balanced Differential Design Inputs (also with RCA)
• Thick, very Low impedance pure copper tracing
  
  
• Generous Power Supply
• 1.55kVA High Efficiency Toroidal using a 129,000uF for 7 Channels (with 3000uF On-Board Capacitance per channel)
• Input Sensitivity 1000mV
• Output Device Type High Power 250 Watt Bipolars - 6 per channel and hand precision matched
• Input Impedance Nominally at 23,000 Ohms
• Power Output at 8 Ohms 200 Watts
• Power Output at 4 Ohms 400 Watts (Doubles Down)
• Frequency Response 10Hz - 90kHz +0/-3dB
• Output Impedance 0.006 Ohms
• Signal-to-Noise Ratio >100dB @ full power
• Maximum Output Voltage 42 Volts
• Damping Factor (static 8 Ohms) >900
• Gain 29dB via XLR, 35db via RCA
• Slew Rate 75V/µs
• Maximum Peak-Peek Current – 75 amperes
• Crosstalk @ 1kHz > -96dB
• Intermodulation Distortion (IDM) .03%
• Design Methodology True Balanced Differential Design Utilizing DC Servo Direct Coupled Inputs (No capacitors in-line)
• THD (1KHZ) < 0.0015 %
• THD (20Hz - 20kHz @ 200 watts) < 0.05 %
• Power Consumption @ idle 40 Watts
• AC Power Requirements 120V / 60Hz (Single voltage Supply)
• Fuse Replacement Long fast blow - 10A / 15A
• Dimensions (W x H x D, inches) 19 x 8.9 x 21.5 (body width is 16.5 while the face plate is 19” Standard)
• Weight 88 Pounds with 7 channels, 100 pounds shipped.
• Balanced Input Pin Assignment:
• Pin 1 Ground
• Pin 2 Positive
• Pin 3 Negative