Over the past few years, many types of microphone preamplifiers have been introduced, ranging from el cheapo under-$100 units to expensive high-end pieces. The workstation revolution made it easy to convert an acoustic instrument or voice to hard disk with the addition of only a mic preamplifier, allowing subsequent processing in the digital domain within the computer.
|Applications: Studio, live sound, test and measurement
Key Features: Quad ZDT solid-state microphone preamp; differential circuitry throughout; balanced XLR and unbalanced 1/4-inch outputs; internal power supply
Contact: Earthworks Audio Products at 603-654-6427 Web Site
It should be no surprise that the sonic quality of these microphone-amplifying devices varies, with circuit topologies built around either vacuum tubes or solid-state devices. Recently, use of high-quality op-amps (not 5534s) has made it possible to rival - and in some cases surpass - the sonic capabilities of discrete transistor designs. One such product is the Earthworks 1024.
David Blackmer's new differential design is called Zero Distortion Technology (ZDT). The Earthworks 1024 ($3,500) is referred to in the preliminary owner's manual as the "perfect preamplifier times four channels." Perfect is a pretty strong word, especially for a piece of pro audio gear. No equipment is perfect, but when it comes to accuracy, the 1024 comes closer than just about anything I have heard.
The primary signal path is differential, or balanced, from input to output. Many designs have balanced inputs and outputs, but are single ended or unbalanced internally. This is done to save money while still claiming to be professional by sporting XLR connectors. Staying balanced all the way has several advantages, not the least of which is the ability to cancel out even-order distortion, hum and noise.
The 1024 has four channels, an internal power supply, and is packaged in a one-RU-high box. More often than not, a super low noise and distortion preamp like this has an external supply, so it is quite an achievement to get super specs with a hum-producing power transformer in such close proximity.
The front panel is well laid out. A large control labeled Decibels Gain switches from 5 to 60 dB of gain in 5 dB steps. This signal feeds the rear panel XLR output labeled ZDT Balanced Stepped Out. A smaller variable output control feeds a 1/4-inch unbalanced rear panel connector. This control provides 20 dB of gain reduction after the stepped gain control and is 6 dB below the balanced output when fully open.
Earthworks highly recommends using this unbalanced output when feeding unbalanced inputs. The first time I used the 1024 I mistakenly used the XLR output to feed the XLR input of a Millennia EQ, which happens to be unbalanced, only to hear some of the most unusual and unpleasant distortion I have ever heard. Bottom line - the Earthworks 1024 sounds best when you use the XLR outputs feeding balanced inputs.
Miniature toggles are used to switch 48V phantom power and signal polarity. A "Standby" toggle is handy when changing microphone cables to avoid sending speaker cones into orbit. LEDs indicate phantom power status and clipping. The clip LED flashes when the signal at the stepped output reaches a maximum level of 28V, which is 3V below the 1024's actual clipping point of 31V max, which in dBu-land is equivalent to just over +32.
Tons of headroom, in addition to an incredibly low noise floor, equates to some serious dynamic range. Specifications include an equivalent input noise of -143 dBV at 60 dB gain (A-weighted). Frequency response is rated from 1 Hz to 200 kHz +/- 0.5 dB, while THD is said to be less than 1 ppm or 0.0001 percent.
Because these specs seemed extraordinary I asked a colleague of mine to perform bench test with his Audio Precision System Two Cascade. His measurements confirmed that the 1024 either met or came very close to the claimed specs of Earthworks. At these extremely low levels of distortion and noise, the location on this planet where you do your measurements can make a difference.
I used the Earthworks 1024 on several sessions with a number of mics and with many different musical instruments. It is about as transparent as anything I have heard. The sound is completely uncolored and noise is just about as low as it gets.
After the first blunder of trying to drive an unbalanced input with the 1024's balanced output, then using the unbalanced output to drive an unbalanced input, it becomes perfectly clear that the real beauty of this pre-amp is to use it in the balanced mode whenever possible.
If you are looking for quality recording mic preamplifiers to feed unbalanced inputs, you may find ones that do better and cost less. But if you are looking for the ultimate in transparency, low noise, high headroom, low distortion and coloration (and use it to feed a balanced input), the Earthworks 1024 is a perfect match. It is a fine piece of precision audio equipment.