Legacy Monobloc Power Amplifier and High-current Preamplifier

Known primarily for its factory-direct sales of high-end loudspeakers, Legacy has been delivering a line of equally impressive electronics.
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Known primarily for its factory-direct sales of high-end loudspeakers, Legacy has been delivering a line of equally impressive electronics.
Product PointsApplications: Recording studio; mastering

Key Features: Monobloc: high current and high voltage output capabilities, balanced differential; Legacy preamp: remote line-level amplifier, precision level operation control

Price: Monobloc: $2,400 each; Legacy preamp: $1,595

Contact: Legacy Audio at 800-283-4644
The monobloc amp

The Monobloc is Legacy's flagship power amplifier, producing 800 W continuous into 4 ohms and 450 W continuous into 8 ohms. The design is a collaboration between Legacy's Bill Dudleston and Eric Lauchli of Coda, a well-respected, high-end electronics company. One of the primary design goals was to build an amp that can deal with the range of impedances found in many of today's speakers.

Legacy designers believe that to deliver power consistently into a wide range of impedances, an amplifier needs to have both high-voltage and high-current output capabilities. High current alone is not enough.

The Monobloc has 20 pairs of matched output devices running on 90 V rails, which, coupled with current capability of over 50 amps, makes it possible to deliver peaks of over 1,800 W (with 4 ohm loads)! All this power originates in a supply that has a 940 VA 60 Hz toroidal power transformer with 100,000 µF of capacitance. Other design highlights include balanced differential operation, direct coupling without servo circuitry, no global negative feedback and a slew rate of 50 V/µs without entering Class B operation.

The Monobloc is 17" wide, 6" high and weighs in at 55 lbs. The attractive black-anodized front panel has a large rocker power switch and a nicely sized lighted meter. The rear panel has only an IEC power receptacle, XLR and RCA connectors for balanced and unbalanced inputs respectively.

I listened to the Monobloc's in two different settings with different speakers. First was at Ambient Recording on Dunlavy SC-IV/As fed by a Sony SCD-1 SACD player feeding a Meitner Switchman preamp.

The most immediate and obvious characteristic was the great bottom-end control that this amplifier had over the twin 10" woofers of the Dunlavy speakers. The bass was tight, yet extended down to what seemed like an additional half octave over most amplifiers I had listened to on these speakers. Extended low end, more often than not, results in looseness of the bottom end, but here the Monobloc did a great job of bass extension and control. The Monobloc has the ability to resolve the great detail of space and acoustics, which are redeeming qualities of SACD.

High current preamp

The other listening session was in my studio with the Legacy preamplifier and Westlake Lc-8.1 speakers. SACD again was the source (if you think I'm hooked on SACD for a source, you're right). Different speakers, different rooms the impressions were almost the same: good bass extension with great control of low frequencies; smooth, ear-friendly upper midrange without harshness; remarkable high frequency detail and openness. Without a doubt, this was the best I've heard the Westlakes sound.

The new Legacy remote-control line-level stereo preamplifier also boasts some innovative ideas, which make it stand out against preamps costing lots more. The preamplifier is a high-current design using FETs on the input with zero-feedback Class A complementary followers to drive the outputs.

Like the power amp, the front panel of the preamp is black anodized with simple, well-laid-out controls. Four nice-feeling pushbuttons on the left select inputs, each with a blue LED indicating which input is selected. The center has an illuminated display showing the numeric level of each channel -- more on that later. Three additional pushbuttons activate mono as well as monitor and processing loops.

To the far right is a large rotary encoder, which uniquely doubles as level control and with a slight push turns into a balance control. This is way cool since the numeric readout displays the level of each channel, making it easy to see the offset. The back panel has one set of balanced XLR inputs with three sets of unbalanced RCA input connectors.

Two sets of RCA connectors make it possible to insert both a monitor and a processor loop. This seems a bit redundant to me, but hey. Both XLR-balanced and RCA-unbalanced outputs are available. For pro work it would be nice to have more balanced ins and outs and less unbalanced, but since this is not a dedicated pro piece, I'll stop complaining.

Level control is accomplished with a Crystal Semiconductor CS3310 potentiometer, which is a digitally controlled analog part. A front panel digital display has 100 steps with 1-dB resolution -- nice. The numbers in the default setup indicate dB of attenuation from 00 to 99, but can be reversed to make the larger numbers louder. Kind of a pro/consumer thing, respectively. With this type of digitally controlled analog pot it is possible to have more precise tracking between channels than with a multigang analog pot.

Another great feature is the remote control capability. A small, six-button infrared wireless remote allows you to change level, balance, switch inputs, insert monitor or processor loops, and mute. For pro applications, this is really cool since the actual preamp does not have to be taking up space near the workstation where space is at a premium.

Summary

A preamp should not impose any sonic signature of its own on the sound. It's just line in, line out with some level control and input switching, yet almost all of the preamps I have come across have some sort of coloration. The Legacy stereo preamp and monobloc amp are about as transparent as they come, look good, and are well built with quality parts, nicely laid out and priced fairly.