Mapletree Mellow Boy 6SL7 User manual

MapleTree Audio Design
100 Cli Cres
Kingston, ON
CANADA K7M 1A8
al@mapletreeaudio. om
www.mapletreeaudio. om
Notice
Power supply unit should be plugged into the amplier unit with the tubes in
the correct sockets BEFORE POWERIN UP. 6SL7/5691 goes in front socket and
the 6336/6AS7 /6080 goes in back socket of the headphone amplier unit.
Please allow at least 12 hours for the tubes to burn in since they are new. It is
not uncommon to hear crackling and metal expanding for new tubes. They
require settling in, especially the 6336 which can be particularly noisy in the
beginning since it is trying to remove impurities due to the manufacturing
process from the plate and cathode. It is recommended not to have the
headphones plugged in for about 3 hours when installing a new 6336.
Do Not plug in headphones immediately after the high voltage LED, second
LED, goes ON. One has to allow the output capacitors to be charged up rst. It
is OK if the headphones are constantly plugged in to the headphone amplier
since the high voltage power supply ramps up slowly.
Stacking amplier as shown on manual cover will increased hum. The
6336/6AS7 /6080 are more microphonic than usual. With some headphones
this may not be an issue. Low sensitivity headphones will produce less
audible hum. A magnetic shielding plate, 1/8” - 1/4 “ steel plate, with acoustic
dampening, felt/rubber, can be used between the amplier and power supply
to reduce the hum. If this is still an issue separate the power supply unit from
the amplier unit.
For super sensitive headphones the 6SL7/5691 might require shielding. Just
place a metallic cylinder/ shield over the tube and allow the cylinder to touch
the mounting screws of the socket for the 6SL7/5691.
Do not clean with alcohol or paint thinner. Water damp cloth is su=cient or
dust o>.

Read Manual before operation.

Read Manual before operation.

Mellow Boy 6SL7/6336
Octal Duo OTL Stereo Headphone Amplier
sers' Manual
Rev Dec. 12/19
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 2019
0

Introduction
The Mapletree Audio Design Octal Duo (OD) Output Transformerless (OTL) Stereo Headphone
Amplier represents a high performance development of an octal-based headphone amplier. The use
of a high capacity power supply provides increased power output and a lower driving impedance
employing a widely available 6336 output tube and 6SL7/5691 driver. The separate power supply
chassis allows exibility in positioning each unit and reduces the heat seen by components in the main
amplier chassis. 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 OD OTL power supply.
It is compatible with a 120 VAC line with a frequency of 50–60 Hz. A 1A fuse provides primary
protection for the power supply. nder 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 switches are located on the front panel of the power supply. The LED pilot light indicates
the power on condition. Delayed on allows 30 seconds to warm up tubes before switching on high
voltage, this will increase the life of your vacuum tubes.
1
Fuse Tray
On-Off witch
( Delayed On allows 30 seconds to warm
up tubes before switching on high voltage.)
LED Power
Indicator
AC Power
Input
DC Power
Output

The power supply is connected to the amplier 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 RCA jacks allow connection to a line-level stereo source (e.g. DAC or CD player). The input
impedance is 50 kΩ which is compatible with all source output circuits.
The Mellow Dial at the rear of the amplier unit is to control the softness of the of the music being
played. oftest is when the dial is rotated completely clockwise and crispest when completely counter
clockwise.
2
DC Power
Input Right Channel
Input
Left Channel
Input
Mellow Dial:
oftest clockwise max
Crispest counter-clockwise max

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 32 to 600 Ω are suitable (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 OD OTL 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 OD OTL is supplied with 1 – 6SL7 (driver) and 1 – 6336 (output) tube.
Replacement tubes can be obtained from several suppliers in the . 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. The 6SL7 should have matched sections so as to have a balanced right and left channels.
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 90 days exclusive of shipping cost.
Service, including parts and labor (but excluding shipping), is free within the warranty period.
3
Volume Control
Min. Volume:
Full Counter-Clockwise
Max. Volume:
Full Clockwise
1/4” Headphone

Additional Notes: This manual is an aid to the user for the operation of the OD OTL. 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
manufactures, model and values may vary.
4
6 L7 or 5691
6336
Front
Back

MAD Mellow Boy 6S 7/6336 OD OT Measured Data
Frequency response at 0.1 Vrms output:
Maximum output at 1 kHz:
Po(max) Rload
1.0 W 400 Ω
0.6 W 200 Ω
0.05 W 32 Ω
5

Overload characteristic (1 kHz, 400 Ohm load)
Measured output impedance at 1 kHz: 75.5 Ω
Input impedance: 50 kΩ
Hum and noise at output: less than 3 mV rms (120 dB below max. output)
Recommended load impedance: 32–600 Ω
Phase: non-inverting
Power consumption: 155 W, 120 VAC ( 240 VAC Europe) 50-60 Hz
6
Vout=18.6 Vrms
Vout=21 Vrms

MAD 6SL7/6336 OD OTL Headphone Amplifier
Version:
© Copyright Al P Freundorfer 2019
Rev. November 2019
7