Zesto Audio Andros Téssera phono preamplifier

Maybe you've seen the widely circulated New Yorker cartoon: Two guys stand in front of a nicely drawn, tubed audio system, under which are shelves full of LPs. One guy says, "The two things that really drew me to vinyl were the expense and the inconvenience."

If you can't laugh at that, you've lost your sense of humor—even acknowledging that, oddly, convenience is the raison d'etre of some recent phono preamplifiers—including Dan D'Agostino Audio's Momentum and the CH Precision P1, both of which offer multiple, switchable, configurable inputs saved in memory. Today's well-heeled vinyl enthusiast might have two or more tonearms mounted on a single turntable—or even two turntables, each with two arms. Zesto Audio's new Andros Téssera tubed phono preamplifier takes aim at that market segment.

Zesto Audio's new two-box Andros Téssera tubed phono preamplifier measures 17" wide by 5.5" high by 15" deep, weighs 25 lbs, and costs $12,000. The case is made of 16-gauge steel.

The Téssera is actually conjoined-twin phono preamps, each twin referred to by Zesto as a channel. (The terminology is confusing at first, seeing as how each of those channels also includes left and right stereo channels.) A front-mounted switch lets you choose between Channel A and Channel B. That done, within both channels you can then select between moving-magnet and moving-coil inputs. So the Téssera can handle up to four different tonearms, as long as two of those arms are fitted with MC cartridges and the other two with MM cartridges. (Of course, all those arms could have MC cartridges if the outputs of two of them are directed to their own outboard step-up devices.) In both Channel A and Channel B you can also select one of three gain settings (Low, Medium, High) and, in MC mode, one of 12 loading options: 1000, 800, 700, 500, 400, 350, 300, 250, 200, 150, 100, or 50 ohms. The MM capacitance is fixed at 220pF, and the gain settings are 40, 45, and 50dB. In MC mode, the gain settings are 60, 65, and 70dB.

There are also two MM load options: the standard 47k ohms as well as 68k ohms. Of course, that "standard" is totally arbitrary, because the actual load required for flat response depends on various factors best dealt with in another column. But given the 220pF capacitive load, if you're running an MM cartridge, you should try to use a phono cable of very low capacitance. I've seen the measurements of a Shure M97xe MM cartridge loaded at 47k ohms: anything much above a total capacitance of 250pF will produce serious rolloff of high frequencies above 10kHz. No wonder that cartridge's sound is often described as "polite."


The MC inputs are transformer-based, using top-of-the-line Jensen transformers, with loading ideally applied at their secondary windings. This means that when you select, say, 100 ohms, the resistor value is closer to 15k ohms, with the cartridge "seeing" the transformer's primary coil. The RIAA curve, applied passively, is claimed to be accurate within ±0.5dB.

On the Andros Téssera's neatly laid-out rear panel are, for the A and B channels, three sets each of generously spaced, chassis-mounted inputs: for MM, a stereo pair of RCA jacks; for MC, single-ended (RCA) and balanced (XLR) jacks. There are also left- and right-channel ground-lift toggle switches for the A and B inputs, single-ended (RCA) and balanced (XLR) outputs, and two ground posts.

Inside, both point-to-point and circuit-board-based wiring are used. At the heart of the Andros Téssera is a circuit inspired by those that were first described in the RCA Radiotron Designer's Handbooks of the 1930s, '40s, and '50s. There are six tubes: two pairs of 12AX7/ECC83S dual triodes and one pair of 12AU7s, which drive high-quality output transformers to produce a low output impedance of 150 ohms. The supplied tubes have gold-plated pins and are from JJ Electronics, in Slovakia, and they're plugged into high-quality sockets with gold-plated contacts. There are no solid-state devices in the signal path, which uses only polypropylene capacitors and 1% metal-film resistors throughout.


The outboard power supply, at 17" wide by 5" high by 8" deep and 17 lbs, is almost as big as the Andros Téssera itself, and is as visually homely as the phono preamp is appealing. According to George Counnas, designer of the Andros Téssera and Zesto's president, this supply is "where all the noise is," and so should be placed as far as possible from the main unit, to which it's connected with a 3m umbilical incorporating "special RFI suppression." This cord conducts only direct current, and is terminated with the neatest-operating spring-loaded connector I've ever used.


Keeping It Pure
The switches on the Andros Téssera's front panel, all mounted on a single circuit board, don't carry the audio signals. Instead, they're connected to another circuit board at the rear of the case, where all signal routing and signal processing is done by seventy 12V, reed-type electromagnetic relays. Why so many relays? Consider that switching from the A to the B inputs requires switching everything. These relays, specified to survive "millions of throws," should last longer than you—unless you're seriously into throwing switches.

The Andros Téssera is handmade in the US, is burned in for 50 hours before shipping, and comes with a two-year limited warranty (six months on the tubes). Counnas told me that in the six years since he launched the PS1 phono stage ($4300 when I reviewed it in my March 2013 column), which was later upgraded to the Andros 1.2 ($4700), he's been thinking about ways to improve on the basic circuit topology. The result is the Andros Téssera. I noted that while the Andros 1.2's noise spec is –75dBu below maximum output, the Téssera's is –90dBu. The Andros has gone from very quiet to extremely quiet.

So the question is, do you need two Andros 1.2s—which is essentially what you get in the Téssera? And consider this—can it be all that long before we see an Andros 1.3, incorporating the Téssera's circuit upgrades? On the other hand, if you like the Téssera's flexibility and sound, and can afford $12,000 . . . why not?

Setup, Use, Sound
Setup is simple, as long as you don't insert the 12AX7s in the 12AU7s' sockets, or vice versa. While it's always good practice to lower the volume before throwing any switches on a phono preamp, I never heard so much as a faint tick when adjusting gain, loading, or even switching between preamps A and B. I ran the Andros Téssera balanced out and single-ended in.

After listening to the Zesto for a week as it sat on its supplied rubber feet, I tried a set of Stillpoints' Ultra SS footers. The sound definitely benefited from that. And while every Andros Téssera is broken in for 50 hours at the factory, the sound definitely improved after another 30 or so hours of playing time.

Zesto Audio
3138 Calle Estepa
Thousand Oaks, CA 91360
(610) 853-9171