The MicroZOTL circuit was born in 2000 as a showcase for the newly invented ZOTL output stage. It was designed to be simple, small, and to sound incredible.

When LTA reintroduced it in 2015 we added preamp outputs and realized that every system we listened to sounded better with the MicroZOTL in the chain. This led to the creation of our reference MicroZOTL Preamplifier.

• Overbuilt linear power supply: Custom, center-potted toroidal transformer with separate windings for the analog and digital sections of the circuit; extremely low-noise Belleson regulator designed for audio with low output impedance, high bandwidth, and excellent transient response; over 100,000uF of storage capacitance, more than is typically found in power amplifiers.

• Ceramic circuit boards: Comparing ceramic PCBs to standard materials is similar to comparing different insulation material used for wire. Most standard wire uses PVC, while higher performance wire uses a fluoropolymer like PTFE. Ceramic PCBs have a lower dielectric constant and absorb less energy from the signal, which gives better clarity and detail.

• Optimized preamplifier output: The preamp and headphone outputs were given separate coupling components, allowing us to use components ideally suited to each and maintain the excellent headphone amplifier performance of the MicroZOTL.

• High-resolution volume attenuator with integrated balance control: An 8-bit relay-based stepped attenuator provides 0.5dB steps for precise level adjustments. Each channel is independently controlled, ensuring that balance adjustments can be made without additional circuitry or degradation of sound quality. The use of low noise, high stability tantalum nitride (TaN) precision thin-film resistors further enhances the accuracy and consistency of the signal. With adjustable gain and step settings, each input can be configured for optimal performance with any given source.

• Transformer-coupled balanced inputs: To take full advantage of balanced sources we employ premium Lundahl input transformers on the XLR inputs.

• Elegant, North American-made chassis: The casework is designed by award-winning, Richmond, VA-based Fern & Roby.

As other LTA product development brought advances in performance, we felt a foundational change was required to elevate the MicroZOTL Preamplifier to its highest conceptual potential. For Level 3 we completely reimagined the audio section: redesigning the boards, redrawing the layout, re-evaluating components, and tuning the circuit.

Using a single larger circuit board instead of several smaller ones let us significantly shorten the signal path and reduce the number of interconnections, which removes opportunities for noise to enter the circuit. Combining the boards also meant that more of the signal path travels on the ceramic PCB. A larger board also gives us enough room to use the best quality components and optimize their placement—including the addition of new, premium coupling capacitors from Amtrans and Jupiter Condenser. These physically larger components allow for lower ESR (Equivalent Series Resistance) and higher phase accuracy. This improved coherency and accuracy across the audio band ensures tonal balance and bass authority. Additionally, improving the grounding scheme resulted in our quietest preamplifier yet—a -10dB reduction in mains interference. 

Building on what we’ve learned from hundreds of hours of research and development on our other products, the power stage in the preamp was fully reworked to decrease noise and increase output capability. We tuned the waveform of the ZOTL carrier frequency to optimize efficiency which resulted in a higher maximum output level. This translates into better intelligibility at low listening levels due to improvements in the headroom and signal-to-noise ratio. Shared sections of the circuit are separated to give isolated, dedicated power to each output channel—limiting the potential for crosstalk. The total power storage increased by 70%, to over 200,000uF, with significantly more of that providing instantaneous power delivery right next to the parts that need it. That results in effortless micro-detail and snappier attack to each note. Most importantly, less work for the ear to follow along to dynamic and complex musical passages. Finally, by standardizing our modular impedance converters, we’re now able to precision match their characteristics which greatly improves consistency.

By redesigning our custom components and utilizing more efficient, modern surface-mount parts in critical areas, the ZOTL stage achieves consistently higher performance.

We’ve also added a high voltage delay and a soft-start filament circuit to warm up the tubes more gently. This improves tube life by allowing the cathodes to reach their operating conditions in a less stressful sequence. Better cathode care = longer tube life.

Why This Matters for Listening

• Natural dynamics – Music breathes effortlessly, from the softest whisper to the loudest climax.

• Greater clarity – Fine textures in vocals, strings, and percussion are more discernible.

• Smoother highs – Eliminating harshness often associated with less efficient designs.

In essence, this optimization ensures the MicroZOTL circuit performs at its absolute best, delivering both precision and musicality without compromise.

It’s not just engineering—it’s the difference between hearing music and feeling it.

Amplifier class: Class A, no feedback

Inputs: 4 Stereo RCA single ended inputs using high quality Cardas connectors; 1 XLR transformer-coupled balanced input, with Lundahl transformers. One Tape input.

Outputs: Headphone ¼” Phone jack, dual RCA single-ended preamplifier outputs, Tape Monitor output

Volume Control: Stepped attenuator with two settings. Default: 100 steps logarithmic; High-Res: 199-steps, linear

Gain: +14dB.

Input sensitivity: 0.75Vrms.

Input impedance: Single-ended: 50k ohms, Balanced: 100k ohms. 

Output impedance: Preamp output: 50 ohms, Headphone output: 1.38 ohm.

Frequency response: -0.06dB/+0.1dB from 20Hz to 20kHz, -3dB at 1.6Hz to 110kHz

THD+N: 0.2% at 1Vrms output, 0.43% at 2Vrms output. 

Crosstalk: -65dB at 1kHz.

Hum+noise: Under -110dB at 2Vrms output. 

Power output: into 15 Ohms: 580mW, 30 Ohms: 300mW

Power consumption: ~50W

Input Voltage: 115VAC/230VAC ±10% (User Selectable)

Tube complement: 2× 12AT7/ECC81, 2× 6SN7/12SN7

Dimensions: 17 inches (43.2 cm) wide, 4.2 inches (10.7 cm) tall, 12.4 inches (31.5 cm) deep (including knob and connectors)

Weight: 14 lbs. (6.35 kg.) Shipping weight: 22 lbs. (10 kg)