Tube Preamp Reviews

As I was talking with an audio-retailer friend recently, he reached for a Rolls-Royce metaphor to describe the McIntosh brand. Expensive? Sure, but not as expensive as some boutique high-end products. Fast? Sure, but there are faster things—also bigger things, smaller things, wackier things, and cheaper things.

But when you look at a Rolls or a Bentley, you immediately recognize it for what it is, and you want to sit down in it. And so it is with McIntosh, except you don't want to sit down in it; you want to sit down in front of it, between the speakers of the hi-fi system it occupies.

History matters. When a new model from Bentley appears, there is a connection to what came before it, a long tradition. There is no pretense of reinventing wheels; instead, it's about rolling those wheels a little farther on down the road. That heritage results in a comforting familiarity. From the first audio products McIntosh offered, in 1949, down to the present lineup, any knowledgeable consumer can look at it and immediately know what it's for and recognize its value. In particular, people value a legacy of quality, especially when so many older, vintage products are out there and still working. It feels good knowing that the thing you're buying is likely to last and be enjoyable and satisfying to use for a long time.

The C12000 is McIntosh's current flagship preamplifier. It's part of McIntosh's Hybrid Drive series of products that combine tubes and transistors in interesting ways. The first McIntosh product to incorporate such a mix—although it preceded the marketing term by several years—was the MA252 stereo integrated amplifier, released in 2017. It was "hybrid" in the familiar sense, pairing a tubed preamplifier stage with a 100W solid state amplifier. The range has since expanded to include amplifiers, preamps—even a CD/SACD player.

Currently, McIntosh offers eight preamplifiers, but only the C12000 is Hybrid Drive. This prime-cut, all-analog, dual-chassis model, with separate boxes for the power controller unit and the signal-path circuitry, continues a line started with the solid state C100, McIntosh's first two-chassis preamp, which was introduced in 1997. The C100 was followed eight years later by the C1000, a hybrid device: You could choose either the solid state chassis (C1000P) or the tubed chassis (C1000T), or you could get both preamp chassis and the C1000C controller for $26,000. The C1000 was succeeded in 2015 by the C1100, but, though also a dual-chassis preamp, the C1100 was all-tube.

The C12000, which is now McIntosh's flagship stereo preamp, returns to the C1000's hybrid approach, but now both sets of electronics, tubed and solid state, occupy a single chassis—two chassis altogether including the controller. With the C12000, the price for a flagship McIntosh dual-mode preamplifier has fallen by a lot, to $16,000.

Separation of powers
The first thing to note about the two-box C12000 (after noting that there are two boxes) is that although they are freestanding, the two chassis must be joined by a pair of 3'-long cables terminating in proprietary 23-conductor connectors. Three feet isn't long, so the two preamp boxes need to sit side by side or perhaps vertically with suitable separation; McIntosh says don't stack them. (In fact, in the owner's manual, McIntosh suggests cutting a hole in the shelf above to ensure adequate ventilation.)

Fit'n'finish is superb. Both chassis feature the same load-bearing handles found on other premium McIntosh models; the handles are both functional and aesthetic. Aesthetics are further enhanced by the traditional, backlit McIntosh logos against black glass and, on the preamplifier module, a pair of meters that glow blue and windows that display green-illuminated 12AX7 tubes. Captain Nemo would dig it.

I asked McIntosh whether this two-box approach improved the preamp's specifications. Joe Guelzow, McIntosh Labs' electronic design engineer, responded: "Yes, when compared to other tube preamplifiers we produce at McIntosh, reduction in noise can be [lower] by at least 4dB and even 10dB, depending on the input. The dual-chassis design completely separates all power supply, microprocessor, and control circuits from the pure audio circuits for total noise isolation." The specified S/N ratio of the high-level output is rated at an impressive –107dB (A-weighted), measured at 2.5V. If that's accurate, this is an exceptionally quiet preamplifier (footnote 1).

Unusually for a two-channel preamp, the rear panels of both chassis are relatively full. The controller's back panel is dominated by trigger inputs and outputs on 3.5mm mini–stereo jacks, intended to control other attached McIntosh components, sending remote-control signals and turning the lights on and off. The only other connectors on the controller's rear panel are a USB port for factory updates and the left- and right-channel connectors for the custom, 23-pin umbilical cables that connect the control module to the preamp module. An AC power cord socket completes the picture.

A glance at the preamp module's back panel gives an idea of what the C12000 designers were aiming for. It's what you don't see: There aren't any digital inputs. There's no DAC on board, just lots of old-school analog RCA and XLR jacks: six pairs of balanced line inputs and four pairs of single-ended line inputs plus two pairs of single-ended inputs for the phono stage. For outputs, there are two pairs of balanced, a pair of unbalanced labeled "Main," and another pair of unbalanced labeled "Rec/Fixed out." The two pairs of balanced outputs are labeled "1-SS" for solid state, "2-T" for tubed. To switch from solid state to tube, you switch from output 1 to output 2. The unbalanced Main outputs can be set to either tube or solid state via internal settings.

Here's another thing you won't see on the C12000, even behind the scenes in setup mode: tone controls. Other McIntosh preamplifiers have tone controls, whether accessed via internal menus or maybe staring you in the face as on the C53 preamp and its eight-knob front-panel equalizer. The C12000 is obviously intended as a minimalist, high-performance preamp. Joe Guelzow again: "Integrating analog tone controls into a system such as this one would also introduce noise, due to the amount of components needed to be able to integrate analog tone controls. Alternatively, digital tone controls could also introduce their own high-frequency noise while also taking away from the 'pure analog' many enthusiasts desire." Include me out. I don't want tone controls and wouldn't use them.

The phono stage is tube-based; there is no solid state option. For this reviewer, that is totally cool, as it allows for trying different combinations of tube and solid state amplification. You can use a tubed phono stage into a solid state line stage. You can run a solid state output to a subwoofer and send the tubed output to the loudspeaker amplifiers.

Moving on to front panels: The preamplifier module's front panel is simple. Beyond the aforementioned logo, meters, and tubes, the only front-panel element is a ¼" headphone jack, about which more later.

The controller's front panel is where the operational action takes place. Two large knobs control Input and Volume. Two small knobs operate various setup controls. Four push switches are labeled Setup, HXD, Mute, and Standby/On. In the middle is an information window.

Operating in tandem with the controller unit is a large, multi-purpose remote control—almost a wand, really—measuring 9½" long. It's what you'd call "Universal," able to control other components in your system, McIntosh components in particular.

Internal affairs
What's inside? Ron Cornelius, McIntosh product specialist, gave me an overview: "The most important difference between the C12000 and all other McIntosh preamps is, it is both dual mono and fully balanced. ... In the C12000 control module, each channel's power supply has its own R-core power transformer, and in the C12000 preamp module, each channel has its own circuit boards. The C12000 has twice the parts installed in twice the chassis to achieve the highest possible performance as compared [for example] to the C2700 preamplifier. Balanced circuits, like balanced cables, will cancel induced noise." Design engineer Guelzow piled on: "The tube circuitry is specifically tuned for the 12AX7As and 12AT7 vacuum tubes utilized in the C12000's circuits, while the solid state channels utilize a discrete, high-fidelity, fully differential audio operational amplifier to drive their outputs."

For some time, I have pondered the relationship between performance specifications published by manufacturers and the actual, audible results. How do measurable factors such as distortion and signal-to-noise ratio relate to subjective soundstage and timbral quality? I asked Ron Cornelius to share his/McIntosh's opinion: "McIntosh designs for the lowest possible distortion and highest signal to noise. These two are often related. As to sound quality, image size, and dynamic range, the total gain of the preamp and the maximum voltage output are important. The C12000's maximum output voltage range is higher than our other models, at 10V RMS unbalanced and 20V RMS balanced."

The C12000's 12AX7A-based tubed phono stage achieves outstanding specifications; 0.05% THD, S/N ratio of 83dB (A-weighted). There are two single-ended phono inputs. Instead of one being dedicated to moving magnet, the other to moving coil, as is often the case, each input can be adjusted as desired. Resistive and capacitive loading and gain settings can be set independently for each. Two MC cartridges? No problem. Users who run two tonearms or turntables are provided for.

You may not get a DAC with this C12000 meatball, but you do get a high-power, class-A headphone amplifier, output from that ¼" jack on the preamplifier module front panel. You can choose from three gain/ impedance settings for optimal headphone matching. And there is one unique, defeatable headphone setting, which McIntosh has trademarked with the acronym HXD: Headphone Crossfeed Director. When engaged, this circuitry crossfeeds portions of the left- and right-channel signals to more closely match the experience of loudspeaker listening—to liberate the stereo image from inside your skull.

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Footnote 1: As I was editing, it occurred to me that S/N ratio would be different for the tubed and solid state sections—wouldn't it? I sent a note to Guelzow, who was kind enough to measure the S/N ratio for the sections separately. His results, via the balanced outputs: 109.1dB at the solid state outputs, 108.8dB at the tubed outputs. Why are these numbers so much higher than JA's? Guelzow's measurements were made at 2.5V; John's were made at 1V. That's a difference of 8dB. Assuming a fixed noise level, this brings the two sets of measurements precisely into line.—Jim Austin