MicroZOTL Level 3

About the MicroZOTL Level 3

The MicroZOTL Level 3 is Linear Tube Audio's flagship ZOTL-based Class A tube preamplifier and headphone amplifier, designed and hand-built in Maryland around David Berning's patented Zero hysteresis Output Transformer-Less architecture for very low output impedance and high linearity. Its non-feedback, pure Class A design achieves exceptionally low output impedance from the 6SN7 stage, yielding fast transients, fine harmonic detail, and deep, controlled bass while preserving the tonal richness of vacuum tubes. The preamp provides 4 stereo RCA single-ended inputs with Cardas connectors, 1 XLR transformer-coupled balanced input using Lundahl transformers, plus a dedicated tape input, giving a total of five analog inputs. Outputs consist of a front-panel 1/4" headphone jack, dual RCA single-ended preamplifier outputs, and a tape monitor output. Volume is controlled by a relay-based stepped attenuator with two user-selectable modes: a 100-step logarithmic curve and a 199-step high-resolution linear curve, offering precise level setting and channel matching. Electrical performance includes gain of +14 dB, input sensitivity of 0.75 Vrms, single-ended input impedance of 50 kOhm and balanced input impedance of 100 kOhm, preamp output impedance of 50 Ohm, and headphone output impedance of 1.38 Ohm. The measured frequency response is extremely flat at -0.06 dB/+0.1 dB from 20 Hz to 20 kHz, extending to -3 dB points at approximately 1.6 Hz and 110 kHz, with low THD+N (0.2% at 1 Vrms, 0.43% at 2 Vrms), crosstalk around -65 dB at 1 kHz, and hum and noise below -110 dB at 2 Vrms output. As a headphone amplifier it delivers about 580 mW into 15 Ohm and 300 mW into 30 Ohm, making it suitable for a wide range of dynamic headphones while prioritizing refinement over sheer power. The tube complement is 2x 12AT7/ECC81 and 2x 6SN7/12SN7, allowing tube rolling between 6SN7 and 12SN7 types. Physical specifications are 17" wide, 4.2" tall, 12.4" deep, and 14 lb, with power consumption around 50 W and user-selectable 115/230 VAC mains input. The Level 3 implementation incorporates upgraded signal-path components, power-supply architecture, and layout refinements over earlier MicroZOTL preamp versions, positioning it as a reference-grade line stage and headphone amp recognized for its transparency, low noise, and musical detail.