Introduction
The Mapletree Audio Design Octal Duo (OD) 300 Stereo Headphone Amplifier represents a high
performance development of an octalbased headphone amplifier. The use of a high capacity power
supply provides increased power output and a lower driving impedance employing a widely available
6AS7G/6080 output tube and 6SL7/5691 driver. The separate power supply chassis allows flexibility in
positioning each unit and reduces the heat seen by components in the main amplifier chassis. Premium
components include Tantalum film resistors in the driver stage.
I
nput/Output Connections
The standard IEC line cord is attached to the receptacle on the rear panel of the OD300 power supply.
It is compatible with a 120 VAC line with a frequency of 50–60 Hz. A 1A/250 V fuse provides primary
protection for the power supply. It is located under the chassis and can be accessed by removing the
bottom cover of the power supply with the unit unplugged and waiting 3 minutes after powering off.
Under normal conditions, it should not be necessary to replace the fuse. If power fails to come on, you
can check the fuse and replace with a spare if necessary. If the fuse blows a second time,
you should not try to operate the unit. Contact Mapletree Audio Design for information regarding
service.
The power supply is connected to the amplifier chassis with the supplied power interconnect cord.
Never power on the power supply without making this connection. The two chassis may be stacked or
separated as permitted by the power interconnect cord.
The power switches are located on the front panel of the power supply. The heater switch needs to be
turned on first. Allow the heater to warm up for about one minute before turning on the high voltage
switch. This will increase the life of your vacuum tubes. The LED pilot light indicates the power on
condition for the heater and high voltages. Both lights have to be on for the OD300 to be functional.
Switch the high voltage off first and wait for about 10 seconds to allow the high voltage capacitors to
discharge. Lastly, switch off the heater supply. The heater supply is not a standby switch. If one leaves
the heater switch on, it will eventually burn out.
The RCA jacks allow connection to a linelevel stereo source (e.g. CD player) while maintaining the
connection to the regular amplification system. The input impedance is 50 k which is compatible with
Ω
all source output circuits.
1
Fuse Tray
AC Power
Input
DC Power
Output
