The TENSA Tube Phono Stage: What Makes It Special
The Most Critical Link in the Vinyl Chain
The signal coming off an MM cartridge is just 3–5 millivolts — hundreds of times weaker than a line-level signal. Before it can reach the mixer, it has to be amplified and equalized along the RIAA curve, and all of that is done by the phono stage: the very first stage the sound from a record passes through.
This is where the fate of the entire sound is decided. Any noise or distortion added here gets amplified along with the music and can never be removed. That is why the phono stage in TENSA is not an auxiliary chip tucked into a corner of the board, but a full-fledged Class-A tube amplifier.
The Vasilyich Circuit: A Folk Legend of DIY Hi-Fi
At the heart of TENSA's phono stage is the so-called "Vasilyich circuit" — a tube phono preamp design that became genuinely legendary in the DIY hi-fi community of the 2000s and 2010s. Its author is known by the nickname "Vasilyich" on audio forums. The circuit was discussed, built and refined across dozens of communities; one of its popularizers alone built more than 150 units.
The reason for that popularity is simple: the circuit is straightforward enough to build, yet sonically it stands up to far more expensive commercial designs. Its principles — a radically simplified signal path and the rejection of feedback — link it to the classic American designs of the golden age of vinyl.
How It Works
The TENSA phono stage is a two-stage tube amplifier running in pure Class A. The key design decisions:
**Passive RIAA equalization.** Every equalizer contains resistors and capacitors — the question is where they sit. In most phono stages, the RIAA network is placed inside the amplifier's feedback loop. In TENSA, the equalization is passive: the RC network sits directly in the audio path, between the gain stages. The signal simply passes through it — nothing more.
**No feedback.** There is no negative feedback in the gain stages of the phono stage. The sound is not "combed over" after the fact — it is simply amplified honestly, the first time. The result is transparency and naturalness with none of the artifacts of feedback.
**A minimal signal path.** The phono stage circuit consists exclusively of tubes, resistors and capacitors. No ICs, no transistors anywhere in the signal path.
Aerospace-Grade Tubes
The phono stage runs on miniature dual triodes developed for the aerospace industry — a world where failure is unacceptable and replacement is impossible.
They are rated for 10,000 hours of operation with no degradation of parameters. That is why the tubes are soldered directly to the board, with no sockets: the contact is more reliable, interference is lower, and replacement is simply never needed. This is a deliberate rejection of "tube rolling" — the TENSA phono stage works as a finished instrument, not a construction kit.
Power: Silence Starts at the Wall
A phono stage handling millivolts at its input needs impeccably clean power. TENSA's power supply is external and fully linear: a custom toroidal transformer with a dedicated high-voltage winding for the tubes' anode supply, and complete galvanic isolation from the mains. No switching converters anywhere near the audio.
The measured result: the phono stage noise floor is −80 dB, confirmed by independent bench measurements. For a tube preamp amplifying millivolt-level signals, that is dead silence.
One of a Kind
The market for boutique two-channel analog mixers built for vinyl is small, and we have studied it closely. Tube mixers are rare in it — and not a single competitor offers a built-in tube phono stage: vinyl is usually handled by a transistor or IC preamp, or by an external phono stage.
TENSA, with its built-in Class-A tube phono stage and a line/phono switch on every channel, is effectively the only mixer in the world in this format. The record enters a tube signal path from the very first millivolt.
Not "Warm Tube Sound"
One important note: the tubes in TENSA are not there for fashionable "warm coloration." Quite the opposite. The entire circuit design serves a single goal — maximum transparency and minimum distortion. A feedback-free tube phono stage is not an effect here; it is the most honest known way to amplify the signal from a record: clean, detailed and natural sound — the way it was recorded.