Two problem areas were separation and THD. Diamond rates separation at 80dB. With the amplifier unloaded, this spec was easily met. But, the separation fell to 50dB at 1kHz with four 4-ohm loads connected. This indicates an internal layout problem. I'd like to take this time to clarify what this really means in terms of sound quality. The properties of an amplifier such as separation and damping are often misunderstood and as a result are often given more importance than they deserve. What does 50dB of separation really mean? Let's say that you have 100 watts of music coming out of the right channel. With 50 dB separation you would have just 1/1000th of a watt leaking into the left. Take an audiophile's $1000 phono cartridge: 50 dB would be quite respectable. The same phono cartridge's separation would fall to only 25-30 dB at 20kHz! So, don't let this spec throw you off. For an amplifier, peak output current capability, slew rate, and ability to drive reactive loads are far more important parameters.
Another area where the amplifier fell short is THD. The D7054 was close to Diamond's spec with only one channel loaded, but rose to .09% @ 1kHz with all four channels loaded into four ohms. This indicates the same internal grounding problem discussed earlier.
Damping Factor measured greater than 300. Anything over 50 is gravy. I'd like to take this time to dispel another myth, that super high damping factors make an audible improvement. A damping factor of 50 means that the amplifier's actual output impedance divided into the load impedance is 50. In this example the amplifier's internal impedance is .08 ohms. A typical four ohm speaker typically has 3.2 ohms of internal DC resistance. So, the actual damping factor could not be better than 4/3.2 = 1.25! That is why emphasis on ultra high damping means nothing sonically.
The amplifier passed our reactive load test, working flawlessly into all of our reactive loads. Efficiency at full power into 2 ohms was 54%. At 1/3 power the efficiency fell to 36%, which is typical for class A/B amplifiers.
Listening TestWe tested the Diamond with Morel Duets and the Altec Lansing Voice of the Theater speakers. These old Voice of the Theater speakers are extremely efficient and help to reveal distortion at low power. The amplifier was completely neutral; we could not detect any coloration of the music. The amplifier was silent when turned on, but made a very slight tick when turned off.
ConclusionThis is a great sounding amp; it looks fantastic, and has very versatile crossovers. The cosmetic and build quality of this amp is quite substantial. A bit pricey, but beautiful nonetheless.
Brand: Diamond AudioModel: D7054MSRP: $849.99
| Output power @1% THD 1kHz 14.4 volts |
| Stereo @ 4 ohms | 4 channels x 53 watts |
| Stereo @ 2 ohms | 4 channels x 97 watts |
| Bridged @ 4 ohms | 2 channels x 195 watts |
| Output power @1% THD 1kHz 12.5 volts |
| Stereo @ 4 ohms | 4 channels x 53 watts |
| Stereo @ 2 ohms | 4 channels x 96 watts |
| Bridged @ 4 ohms | 2 channels x 193 watts |