Mapletree Viper OTL User manual

Viper OTL Headphone Amplier
Users' Manual
Rev Dec.. 1/1
Mapletree Audio Design
Al Freundorfer
R. R. 1, Seeley's Bay, Ontario, Canada, K0H 2N0
[phone]
www.mapletreeaudio.com
inf[email protected]
© Copyright Al Freundorfer 2016
0

Introduction
The Mapletree Audio Design Viper Stereo Headphone Amplier represents a high performance output
transformerless (OTL) development of a miniature tube based headphone amplier. The parallel
connected 6DJ8 provides an excellent output stage for the SET amplier and is widely available. The
12AX7 driver delivers a high performance headphone amplier with extremely low output impedance
results. Premium components include metal lm resistors and polypropylene lm/electrolytic
capacitors in the driver stage.
Input/Output Connections
The standard IEC line cord is attached to the receptacle on the rear panel of the Viper. It is compatible
with a 120 VAC line with a frequency of 50–60 Hz. A 1A fuse provides primary protection. 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 o. 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 RCA jacks allow connection to a line-level stereo source (e.g. DAC or CD player) while
maintaining the connection to the regular amplication system. The input impedance is 50 kΩ which is
compatible with all source output circuits.
1
Fuse Tray
AC Power
Input
Right Channel
Input
Left Channel
Input

The power switches are located on the front panel. The LED pilot light indicates the power on
condition. Delayed on allows 30 seconds to war up tubes before switching on high voltage, this will
increase the life of your vacuum tubes. The headphone output jacks are two standard ¼" stereo phone
jacks. If your headphones are terminated in a 1/8" plug, an adapter is required (usually supplied with
your headphones). Headphone impedance from 100 to 300 Ω are suitable for use (Although lower
output impedance headphones can be used with limited volume before distortion).
The signal level in both channels is controlled simultaneously by the volume control on the front panel
of the Viper amplier.
Tubes
A tube burn-in period of several hours may be needed to achieve the best sonic performance. Tube life
should be thousands of hours. Aging tubes may result in a reduced gain in one or both channels or an
increase in noise levels. Infrequently, a heater may burn out which is indicated by total loss of sound.
The Viper is supplied with 1 – 12AX7 (driver) and 2 – 6 22 (output) tube. Replacement tubes can be
obtained from several suppliers in the U. S. and Canada. Both types are currently manufactured and are
also available as new old stock (NOS). Some listeners enjoy trying dierent brands and variants of
tubes. The greatest sonic variation will occur with dierent driver tubes. Make sure the driver tube has
match triode sections to obtain the best balance between left and right channels.
2
Volume Control
Min. Volu e:
Full Counter-Clockwise
Max. Volu e:
Full Clockwise
1/4” Headphone
Power Switch
LED Power
Indicator

Warranty
Factory assembled MAD components are warranted for 2 years to the original purchaser for failure of
all parts (excluding tubes). Tubes are warranted for 0 days exclusive of shipping cost. Service,
including parts and labor (but excluding shipping), is free within the warranty period.
Additional Notes
This manual is an aid to the user for the operation of the Viper. Details of the amplier and power
supply circuits are subject to change without notice so as to achieve the best possible performance. The
schematic is only representative of the actual amplier and component manufacturers, model and
values may vary.
3
12AX7
7025
5751
ECC83
ECC803
CV4004
6N2P
6DJ8
6922
7308
E88CC
E188CC
6H23P
6N1P
Front
Back

MAD OTL Viper Measured
Frequency response:
Maximum undistorted output at 1 kHz:
Po(max) Rload
0.2 W 150 Ω
0.1 W 300 Ω
Overload characteristic (1 kHz, 300 Ohm load)
4
Vout=2 Vr s
Vout=5.5 Vr s

Measured output impedance at 1 kHz: 28 Ω
Input impedance: 50 kΩ
Hum and noise at output: less than 8 mV rms (112 dB below max. output)
Recommended load impedance: 100–600 Ω
Phase: inverting
Power consumption: 35 W, 120 VAC ( 240 VAC Europe) 50-60 Hz
5

MAD OTL Viper Headphone Amplifier
Version:2
© Copyright Al P Freundorfer 2019
Rev. Dec. 1st 2019
6