use a tube for output that is normally used for input or intermediate gain stages. The 6SN7 is
respected for its linearity, but prospects for making a high-fidelity output transformer for this
tube are dim indeed. With the high effective turns ratio in MZ2, the 6SN7 works well, and a 2-
ohm output impedance is achieved without using negative feedback.
Amplifier Maintenance
Fuses: The MicroZOTL2.0 has a fuse in the chassis and either one or two fuses in the external
power supply. All are the 5x20mm type. There is a 2.5A fuse on the audio board in the main
amplifier enclosure and there are two 2.5A fuses in the linear power supply enclosure.
Vacuum Tube Replacement: The amplifier operates the tubes in a manner that maximize tube
life. The tubes are expected to give 10 to 20 years of service based on several hours of use per
day. If you choose to change the tubes, be extremely careful to ensure the unit is off for at least 5
minutes to allow voltages to dissipate.
Avoid touching the board, as high voltages may still be
present even if the unit is off.
Ensure the tab on the 8 pin tubes is aligned with the slot on the
tube socket. The amplifier is self-biasing, so there are no adjustments necessary. The tube sockets
we use are very tight: proceed gently and gradually when changing tubes to avoid damage. Any
damage caused by changing the tubes is not under warranty.
Specifications (Typical Performance Values)
• Sensitivity: 0.6V RMS for full output
• Output impedance (measured at 0.5A, 60 Hz): 2 ohms
• Input impedance: 50k
• 100V / 120V / 240V operation: Auto-switching or manually switched with linear power supply
• Hum and noise: minimum 60µV RMS or 90dB below full output (20Hz-20kHz)
• Carrier: -50dB (250kHz)
• Power consumption from ac power source: 33W
• Power output with 4-ohm load: 1W, 1% THD
• Power output with 14-ohm load: 0.5W, 1% THD
• Channel separation (4-ohm loads): 46dB, 100Hz-10kHz
• Channel separation (14-ohm loads): 54 dB, 100H-10kHz
• Frequency response (4-ohm load): +0, -1dB 10Hz-20kHz, full power
• Frequency response (14-ohm load): +0, -1dB 5Hz-50kHz, full power
• Amplifier class: Push-pull Class A, no feedback
• Voltage gain (4-ohm load): 10.3dB
• Voltage gain (14-ohm load): 12.4dB
• Size: 9 1/2 inches (24.1 cm) wide, 4 3/4 inches (12.0 cm) tall, 7 7/8 inches (19.7
cm) deep (including connectors)
• Net weight: 2.5 kg (5.3 lb)
• Finish: Aluminum case with acrylic cover
• Tube complement: two NOS 12AT7/6201 and two 6SN7 or 12SN7
