Mapletree Ear+ HD300 User Manual
Ear+ Purist HD
Ear+ HD300
Limited Commemorative Edition
High Definition Stereo Headphone Amplifier
Users' Manual
Revised Nov. 28/13
Mapletree Audio Design
Lloyd Peppard
R. R. 1, Seeley's Bay, Ontario, Canada, K0H 2N0
(613) 387-3830
www.mapletreeaudio.com
info@mapletreeaudio.com
© Copyright Lloyd Peppard 2013
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Introduction _
The Mapletree Audio Design Ear+ HD300 Stereo Headphone Amplifier is a special
limited edition (2 units made) to commemorate the 300th unit in the Ear+ family of
headphone amplifiers going back to 2002. It utilizes a unique tube set comprising two
EF37A pentode drivers and a 6AS7G dual triode output tube. The passive component
selection includes Panasonic polypropylene film output capacitors, vintage Philips carbon
film resistors, and Auricap polypropylene film interstage coupling capacitors. All tubes
are heated with a dc voltage supply. The high voltage rectification employs a solid-state
bridge of high-speed silicon diodes driving a heavy-duty capacitive filter. Both the heater
and high voltage supplies utilize toroidal power transformers for high efficiency and low
noise.
Input/Output Connections______
The standard IEC line cord is attached to the receptacle on the rear panel of the Ear+
HD300. It is compatible with a 115-125 VAC line with a frequency of 50–60 Hz. A 2-3
A/250 V fuse provides primary protection for the power supply. It can be accessed by
removing the bottom chassis cover. Turn off the power and unplug the unit at least 60
sec before removing the cover. Replace the cover before again applying power. 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.
Two sets of Input RCA jacks are provided on the rear panel, which allow connection to a
line-level stereo source (e.g. CD player) and to the line input of a preamp or integrated
amp without the need for a Y-adapter. The input impedance (with only the source
connected) is 100 k? , which is compatible with all source output circuits. The input
sensitivity is 0.1 V to produce 10 mW power into 32 Ohm headphones.
The headphone output jack is a ¼" locking stereo phones jack with the left channel
connected to the tip contact. The headphones plug is released by depressing the red tab at
the bottom of the jack. If your headphones are terminated in a 1/8" (3.5mm) plug, an
adapter is required (usually supplied with your headphones). Headphone impedances
from 16? to 600? are suitable for use with the HD300.
Controls____
The switch on the left of the front panel turns on the ac power to the amplifier. The power
on condition is indicated by the illumination of the pilot light. It takes about 30 seconds
for the tubes to reach operating temperature ready for use. During this time, you may hear
a low level hum through the headphones, which will then disappear completely.
The front panel volume control acts on both channels simultaneously. Tracking between
channels is typically better than 0.5 dB over the control range.
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