This review page is supported in part by the sponsors whose ad banners are displayed below
Other scenarios where a preamplifier is still welcome is with good old vinyl or when multiple sources are to be employed to require switching. Phono stage output still might need a boost of careful signal amplification whilst other signals will require equally careful attenuation. All in all, a preamplifier is the great adjuster of an audio system. Despite its narrow job description, it has a powerful influence on the final sonic outcome.
The Trafomatic Reference One features five unbalanced line inputs located at the left of the backside next to a ground terminal. Outputs are two pairs of RCA and one pair of transformer-balanced XLR. Two toggle switches offer ground lift and selection between single-ended or balanced outputs. Over at the front there’s the rotary mains switch with blue power LED and the IR eye of the remote control. In the middle of the brushed aluminum fascia sits the motorized Alps Blue Velvet precision pot and at the right the five-step input selector. Both top and bottom plates of the metal clam-shell casing sport ventilation slots to keep the inner workings air conditioned. Four damping feet isolate 10 kilos of preamp mass from the outside world.
Designer/owner Sasa Cokic meant to keep his electronic design as simple as possible but with Sasa ‘simple’ is always somewhat of an understatement. As we saw in his matching phono stage where he found a clever way to keep RIAA correction out of the signal path—a design he shared with the DIY community by providing the circuit design shown in that review—-the preamp too exploits certain distinctive techniques. Even though a preamp needs to be just as quiet as a phono stage but behave as such on either side of unity gain, the power supply is no mere copy of the phono stage. A Trafomatic toroidal transformer now makes up the bulk of the weight. Rectification is commissioned from a choke-filtered EZ80 tube followed by an ECL82 for voltage stabilization. In the review sample the EZ80 was an equivalent Electro Harmonix 6CA4EH.
Of course there are signal tubes too. For voltage gain the Reference One relies on a pair of Russian 6N6Π triodes. For their required cathode bias voltage Sasa uses LED current sources. There are six such light-emitting diodes per channel. When the preamp is powered up, they spread a nice red glow inside spilling softly through the vents. Hence there are no resistors or capacitors doing any biasing. In fact there are no capacitors in the signal path at all. Once amplified, the left and right channel signal proceeds straight to the double C-core output transformer which “sports a very large core to ensure high bandwidth and low output impedance. There's a high-grade grain-oriented M0 silicon-iron core for minimal losses and ultra-low harmonic distortion as well as multi-section windings for minimal leakage inductance and exceptional bandwidth.” The entire circuit is so linear as to require no feedback at all.
Attached to the strip separating power supply and gain stage sits a small red circuit board for the remote controller. This supervises the attenuator's motor drive. In true Trafomatic style the wand is embedded in lacquered wood with an aluminum top. Here control functions are limited to volume up/down.
