Solid State Preamp Reviews

As editor, I love it when Stereophile reviews new equipment. "New" attracts readers. But there are good reasons to review stuff that's not totally new (though usually it is still shiny). The best reason is experience, first-hand: You hear a component at a show or in your own system. You're impressed and decide it deserves a closer look.

That's why I'm reviewing the CH Precision L1 line preamplifier ($34,500 in silver), which has been on the market for several years; meanwhile the company has launched a new, even higher-end preamp, the L10 (footnote 1). But when, recently, I wrote a follow-up review of the CH Precision M1.1 power amplifier, CH Precision loaned me an L1 so that I could experience the pair together. I admired the L1's performance. I really thought we had reviewed it before—we have reviewed most other CH Precision 1-series products—but when I looked I found that we hadn't. I set out to rectify the oversight.

CH Precision products are expensive. This is true for the 1 series, which long seemed cost-no-object; the recently introduced 10 series costs more. But in line with the impressive price, CH Precision products are sophisticated and well-made, with unusual, well-considered features—features that aim not to expand functionality so much as to optimize basic performance. The L1 is very much a purist line stage, if not, perhaps, a minimalist one.

First the circuits
The L1 is fully discrete (no op-amps or other integrated circuits in the signal path), fully balanced, pure class-A, DC-coupled (except when it isn't, about which more later), fully symmetrical, and complementary (which in this context means that NPN transistors are paired with PNP transistors). The designers endeavored to keep signal paths short and the parts count small, especially in the signal path.

The L1, though, goes beyond minimizing self-noise; it monitors and counters DC offset at various points in the circuit and measures and compensates for DC offset on each input.

Input switching is achieved with relays. After that comes a diamond-buffer circuit, which takes the L1's high input impedance and produces a low impedance for the volume-control stage, with no feedback, local or global. "The noise and distortion of such a stage is almost unmeasurable," CH Precision told me (footnote 2).

The L1 is modular and configurable. The configuration I received is dual-monaural (footnote 3), a single chassis with separate boards for the L and R channels. It can also be configured as true monaural, with two chassis, in which case each channel is 100% independent of the other. You can even put two boards in each chassis to expand the number of inputs from eight to 16.

The volume control utilizes a 20-bit R-2R network with precision metal-film resistors, each channel with 236 half-decibel volume steps, covering a 118dB volume range. The volume control circuit operates in current mode and so is followed by an I/V conversion stage.

During a visit to CH Precision's Swiss factory, I got to see the insides of some of the products. They're beautifully made, very clean. A technician was measuring just-finished products on a benchtop; each component the factory sends out has passed an analysis much like the one JA performs. One preamplifier I saw had a power supply with honkin' big capacitors, each big as a water bottle—that would look impressive in a power amplifier. That turned out to be the more expensive L10, but CH takes a similar approach with the L1; they just don't take it as far.

The L1 power supply is shunt-regulated. I asked what the advantages are. "The typical rejection ratio in the audio band for a series linear regulator is 70–80dB; very good ones reject up to 100dB," CH told me. "Our shunt-regulated supplies reject typically 115–120dB in the audioband." The downside to shunt regulation is that it's not efficient. Efficiency doesn't matter in a preamplifier. Noise does.

"Because we rely so heavily on discrete components and circuitry, the power supply takes on special importance and could be considered the foundation of every product we build."

If you think CH didn't go far enough with the built-in power supply, you can add an external power supply, the X1 ($21,500 in silver). CH describes it as "an ultralow noise, discrete, and fully regulated linear power supply, delivering an ultrastable and super clean DC feed to other CH Precision products"—to the L1 preamp, the P1 phono preamp, or various source components, but not the power amps or clock. CH says the X1 has "massive amounts" of powerline filtering and an additional regulation stage.

The L1 power supply has two transformers, the main one, which comes on when the unit is activated, and a smaller one that's on during standby and controls the microprocessor and relays. "When you add the X1, the larger, on-board transformer is taken out of circuit, although the on-board regulation remains in use. The power transformer and regulation in the X1 are used to supply regulated power to the L1." The L1's on-board regulation, then, supplements the regulation in the X1, "creating a cascaded topology to further reduce noise and ripple."

What does that accomplish sonically? CH says it lowers the system noisefloor and increases "dynamic range, resolution and speed of response, transparency, detail, and above all, musicality. Adding X1s to your system will bring intimacy, presence, tonal color and an unmistakable sense of life to your recordings." Each X1 chassis can be configured with either one or two power supplies.

I expressed in an email to CH Precision that their amplification products (including preamps) look like "power supplies with electronics hanging off them." That observation was mainly based on seeing the insides of an L10, not the L1, plus power amplifiers. CH replied, "The power supply is of the utmost importance in all of our designs. Yes, it might well be instructive (if not entirely accurate) to describe the CH products as 'power supplies with a bit of circuitry hanging off them.'"

It must be granted that the electronics hanging off those power supplies are hardly an afterthought.

Next, the features
As I've already said, the L1 has eight line-level stereo inputs; four balanced (XLR) and four single-ended (two on RCA and two on BNC). The L1 has four stereo outputs, two balanced (on XLR) and two single-ended (one each on RCA and BNC). Each input can be disabled or used as a pass-through, and each has gain that's adjustable by ±6dB in 0.5dB steps, to match input levels. As mentioned, the L1 is direct-coupled, but using the menu system and relay switching you can set the inputs one by one to be capacitor-coupled. That's useful if the DC offset for the connected component is above 50mV or so. Similarly, for flexibility, the input impedance of each channel can be set individually, high or low. Each input can be assigned a simple name, which is displayed on the front-panel AMOLED display in big, readable letters and on the app. More on the app in a bit.

The display can be configured for color, brightness, and what information is displayed, via the menu system or the app. You can select mono mode, which sums the L and R channels, and you can invert absolute phase, each with the push of a button. A balance control lets you adjust the L and R channels separately in 0.5dB steps, from +6dB to –6dB. You can set a startup volume, or you can set the L1 to start up at the volume it was playing at when you turned it off. You can set shortcuts in the menu system for frequently used adjustments.

One feature, called "Input Calibration," deserves special mention. It is a process you run during setup, input by input, that detects DC offset at the chosen input and, using "a mix of analog and digital technics," compensates. "Once you start it, it continues until it achieves stability, then it preserves those values," CH told me. The process takes a few minutes.

"In practice, we monitor the 0–10Hz frequency band at 12 specific points in the circuit (six per channel, at the input to the buffer, I/V and output stages), convert the measured values in the digital domain with precise A/D converters, process the signal in a DSP, and apply the bias-mismatch current via small R-2R D/A converters. Obviously, this is way more complex than a pure analog solution, but it allows us to keep the propagation delay of the audio signals constant over time, especially in the bass, and it avoids having to have any capacitors in the signal path." Those digital devices, of course, are also not in the circuit path.

"There are two main benefits to removing the DC offset in the line preamp: It avoids clicks when changing the volume control or switching inputs." The whole time I used the L1, I never heard a click. "It also avoids polarizing the dielectric of the interconnect cables between the L1 and the power amplifier. We feel that this latter effect makes the most significant sonic and musical difference." Which is interesting when you consider that some interconnects have dielectrics that are polarized intentionally.

The L1 has an Ethernet port, but it's only for setup and for app access; the app connects to the network by Wi-Fi and is intended for setup and for music playback. (Firmware updates are carried out with a USB stick.) I found the app intuitive, stable, and easy to use. The only downsides are that, as of this writing, it's available only for Android, and it's a power hog. Unless you shut the app down after every use, you're likely to find your Android tablet out of power when you pick it up the next day. CH Precision is, I understand, in the process of porting the app to iOS.

Day to day I found the L1 simple, intuitive, and a pleasure to use.

The only obvious controls on the front of the L1 chassis are a center knob with a concentric outer ring. Just turn the ring to select a source and turn the inside, smaller knob to adjust volume. The volume knob can also be depressed—that's the On/Standby switch—and the two knobs together with this "button" operate the L1's menu system. And don't forget about the small, chunky, simple remote control, which covers the most important features (source selection, volume, muting) and attaches magnetically to the side of the chassis so it won't get lost.

Setup
I put the L1 on my double-width, four-shelf Butcher Block Acoustics Rigidrack alongside the CH Precision C1.2 DAC and the X1 power supply on the shelf below. The C1.2 (set to fixed volume) was sourced by a Roon Nucleus+ and, sometimes, an Innuos Statement NewGen server/streamer. From Roon, the C1.2 was connected via Ethernet; the Innuos was connected by USB. On the analog side, I used an SME 30/12 turntable (not the Mk.II) with its supplied tonearm and Ortofon Windfeld Ti, Ortofon Verismo, and Lyra Etna λ Lambda cartridges. For phono preamplification and RIAA correction, I used either the Pass Labs XP-27 or the Sutherland Big Loco. Each CH Precision component (including the L1) was on its own shelf—none were stacked—and all used the supplied footers. Amplification was provided by the CH Precision M1.1 stereo amplifier (while it was in for a follow-up review) and later by the Pass Labs XA60.8 class-A monoblocks. These amps drove Wilson Audio Specialties Alexx V loudspeakers.

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Footnote 1: Look for a review of at least one CH Precision 10-series component in the coming months.

Footnote 2: I asked the company how quotes should be credited. PR rep Louise Ford said they should be attributed to CH Precision.

Footnote 3: JA1 points out that "dual-monophonic" is a better description of such topologies than "dual-monaural," which literally translates as something like " two single ears."