The Greek word tessera refers to the number four. Zesto Audio uses that definition (tessera; τέσσερα) to name its latest phonostage. The word is fitting in function since the Andros Téssera ($12,000) phonostage supports four inputs. The word téssera is also defined as an individual tile in a mosaic. What the reader will find out is the “individual tile in a mosaic” is correspondingly applicable to this component since the Andros Téssera also serves as a tile in the mosaic of analog music reproduction.
The Andros Téssera is a vacuum tube phonostage with the ability to receive up to four cartridge/tonearm input combinations. This is accomplished by having two banks (Zesto Audio calls them “Channel A” and “Channel B”) of inputs wherein each bank can receive one moving-coil cartridge and one moving-magnet cartridge connection simultaneously. Selector switches on the front panel set the proper connections while disconnecting the unused ones. When used as intended, the Andros Téssera accepts two moving-coil and two moving-magnet cartridges for a total of four cartridges at the same time. The maximum number of the typical moving-magnet cartridge inputs is two. However, if the user has his own step-up transformer (or Zesto Audio’s versatile Andros Allasso Step Up Transformer) and needs additional moving-coil inputs, one or both of the moving-magnet inputs can be utilized with these external step-up transformers for a total of up to four moving-coil inputs. (More information about the user controls and connections will be described below.)
The four-input capability is one of many changes that Zesto Audio has incorporated in the Andros Téssera compared to its Andros 1.2 phonostage. Besides the control/selector switches being on the front panel of the Andros Téssera (they are on the rear panel of the Andros 1.2), Zesto Audio says that the internal input transformers are of higher quality and larger than those of the Andros 1.2. In addition, there is a larger outboard external power supply, and the tube circuits have been redesigned and are different. There are now two dedicated output tubes (12AU7s) to drive new output transformers—lowering the output impedance to 150 ohms—which Zesto Audio calls a true floating differential output.
The dual-chassis Andros Téssera is shipped in a 20" x 20" x 16" double-walled box (total weight approximately 54 pounds). The main unit and power supply are both inserted in a pair of closed-cell two-tiered foam structures that creates separation and support. Additional items included in the package are JJ Electronics gold-pin vacuum tubes (4x ECC83s/12AX7s and 2x ECC82s/12AU7s), a pair of white gloves (for tube installation), a spade-lugged ground wire (for turntable connection), a 3-meter umbilical cord (for main unit to power supply connection), an AC power cord, and the owner’s manual.
The Andros Téssera’s main chassis (25 pounds) is unmistakably unique (like the rest of the Zesto Audio product line) in the shape and design of its visual features. The mostly black two-tier case with chrome-plated, curved, upper-level divider and grey-colored, curved, front-panel faceplate overlays have an eye-catching charm. The top of the lower tier houses the tube sockets for the 12AX7 and 12AU7 tubes—the sockets are clearly labeled on the chassis. On the front panel from left to right are the Zesto Audio Andros Téssera name and logo, an on/off power switch (the main power switch is on the separate power supply), and two banks of input controls/selector switches that remember their settings when you switch between them. The rear panel has inputs for up to four ’arm/cartridge combos, RCA and XLR output, and a power cable connection input from the external power supply (15 pounds).
On the front panel of the Andros Téssera, the first group of rotary switches within a middle faceplate—identified as “Channel A”—are mc/mm, gain, loading, and channel (bank) controls. Within that “Channel A” group, the mc/mm rotary switch allows mc/mm 47k/mm 68k selections for the two inputs—moving coil or moving magnet (47k or 68k loading for that mm input; mm capacitance is fixed at 220pF). The gain switch allows control of the gain level of low (60dB mc, 40dB mm), medium (65dB mc, 45dB mm), and high (70dB mc, 50dB mm). The loading switch has twelve positions for selecting mc load values of between 50 ohms and 1000 ohms that can be switched on the fly during listening to make selection choice more convenient. These 12 mc load values are electrically located on the secondary side of the step-up transformer in order to allow the cartridge to deliver the full signal to the primary-side of the transformer. The final rotary switch in the group selects the bank inputs for “Channel A” (the selections just described) or “Channel B” (the rotary switch selections in the curved faceplate overlay on the right side of the front panel). An LED will illuminate on the front panel identifying which channel is active. The three remaining switches are duplicates of the mc/mm, gain, and loading for the separate “Channel B” inputs. They have the same function described above but are for the second bank of inputs on “Channel B.”
The rear panel of the Andros Téssera’s main chassis comprises three sections (“Channel A” inputs, “Channel B” inputs, and the phonostage outputs) in addition to the external power supply connection. The “Channel A” inputs have two subsection inputs (mm and mc). The moving-magnet input has RCA connectors for the tonearm cables. The moving-coil input has RCA or XLR (for balanced connection) inputs (the user selects RCA or XLR but not both at the same time). There are two ground switches on the “Channel A” inputs for left and right signal connections that can be used to break ground loops on the inputs if necessary. The “Channel B” inputs have the same functionality as those on “Channel A.” The phonostage outputs have RCA and XLR (for balanced operation) connectors. All of the RCA and XLR connectors on the Andros Téssera are gold plated. There are two ground connectors between the “Channel A” and “Channel B” input sections that allow tonearm and/or turntable ground connections to be attached. The phonostage is also supplied with a single ground cable (spade lugs on both ends) for turntable connection, if needed.