Simaudio Moon Evolution P-7 line preamplifier
Simaudio's Moon Evolution series of products, released in 2005, represents the company's assault on what is possible without constraints imposed by price. All Evolution products feature fully balanced operation and dual-mono circuits; Kalman Rubinson reviewed the Moon Evolution P-8 dual-chassis preamplifier ($13,500) in November 2006. Its power supply and control circuitry are isolated in one chassis, and its audio circuitry in a separate "clean" chassis, an arrangement first seen in 1999, in the Mark Levinson No.32 preamplifier. "From first power-up, the Evolution P-8 performed faultlessly and impressively," Kal wrote. "It was, by far, the quietest preamp I have ever (not) heard. Even with my ear to a tweeter and the volume full up, I could hear absolutely no difference between Standby and Operate. . . . For this time and in this place," he concluded, "the P-8especially when paired with the W-8 [250Wpc power amplifier]is as good as it gets."
I will eventually give a listen to the P-8 for myself, but thought it would be best to prepare for that experience by reviewing Simaudio's more affordable Evolution P-7 preamplifier ($6900).
The Evolution P-7 offers the same basic circuitry as the P-8, but houses it in a single chassis along with the control circuitry and power supply. Even so, the P-7 still qualifies as a dual-mono design: each channel is powered by its own 10VA-rated toroidal transformer. (A third 10VA transformer powers the control and other housekeeping circuits.) Total power-supply capacitance is a whopping 44,000µF divided between the two channels, and Simaudio says there are five stages of DC voltage regulation, as well as extensive use of choke (inductor) filtering of the supply rails.
Other than the single-ended input and output jacks and the control and display circuits, all of the P-7's circuits, including the three power-supply transformers, are carried on a single, large, four-layer printed circuit board. This runs the full width of the chassis and extends about three-quarters of the way toward the front panel from the back, and features thick copper traces, with extra-wide traces used for the grounds. The bottom layer is used for power-supply connection, the second layer for the ground plane, and the other two layers for the audio signal traces. The audio circuitry is fully balanced and implemented with high-quality op-amps. No global negative feedback is used, and there are said to be no capacitors anywhere in the signal path.
Signal paths are kept as short as possiblejust 8" from input to output, per Simaudio's product descriptionthis made possible by the use of an electronically controlled volume control. (The knob on the right-hand side of the front panel operates a continuous-action rotary encoder rather than a conventional potentiometer.) Called by Simaudio the M-eVOL, this control comprises a pair for each channel of R-2R resistor ladders similar to those in DAC chips, one ladder to handle the signal's "hot" phase, the other its "cold" phase. The resistorslaster-trimmed in IC arraysare arranged to give 1dB steps between settings of "0" and "30," and 0.5dB steps between "30" and the maximum setting of "80." (There is also a full Mute, selectable from both the remote control and a front-panel button.) Switching between the resistors is said to be via a discrete relay network, but I could hear no mechanical relay noise coming from the chassis while I was operating the volume control.
The use of an electronically controlled volume control means that each input can have its gain offset by up to ±10dB, and its maximum volume set individually. Each line input can also be configured to be "home-theater ready," with the P-7's volume control bypassed.
The P-7's rigid, solid-feeling chassis offers the same combination of black-anodized and natural aluminum surfaces seen in all Moon Evolution models, and sits on conical metal feet. The center of the front panel is occupied by a large, eight-character, dot-matrix display of red LEDs, beneath which are four discrete pushbuttons for controlling source selection and setup. Two more pushbuttons to the display's right control Mute and Tape Monitor; two more to its left put the P-7 in and out of Standby and adjust the brightness of the display. (At its brightest, the display is legible not only from across the room, but from the next county.)
The input and output jacks are arranged as mirror images for the two channels across the rear panel, with, from outside edge to center: four unbalanced input RCAs above, two balanced input XLRs below; two unbalanced output RCAs and tape-loop RCAs above, a single balanced output XLR below. At top center are the RS-232 and SimLink ports; at bottom center are the 12V trigger jacks, an RJ45 Comms port, two 4-pin XLRs enigmatically labeled "DC Output L" and "R," the IEC AC receptacle, and the power switch.
The lacquered aluminum remote control is hefty enough to serve for personal defense. Apart from the Set-Up and Display buttons, it duplicates the P-7's front-panel controls and adds Channel Balance buttons. It also has controls to operate a Simaudio disc player.
Fly Me to the Moon
Like other Simaudio products I've auditioned, the P-7 took a long time to break in. There was a slight upper-midrange glare to its sound when first plugged in that took a couple of weeks to dissipate. But dissipate that glare indeed didnor did it reappear, even when I left the preamp turned off for a day or so.