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High Fidelity Engineering Co.
OPERATION MANUAL
Model MLB
Zen Triode Headphone Amplifier
INTRODUCTION
This wonderful single ended triode amplifier was designed to drive headphones between 30 ~ 600 ohms without
compromise! Ideal with headphones like
Grados, BeyerDynamics, Sennhiesers
and even the difficult to drive AKG
K1000s will sound spot on the mark.
The amazing detail and openness are no
accident and I'm reasonably certain that
once you have one, it will become your
little buddy too! If you're listening to a
headphone jack on some piece of equipment you'll no doubt either wonder
what all the fuss is about headphones...
or why a person would need a dedicated
headphone amp? After you hear one
you'll wonder why they bother to put
headphone jacks on CD players and
preamps anyway. There is a reason for
dedicated headphone amps and if you
already have one you might want to
read on and see how it stacks up
against this.
DESCRIPTION
Dedicated all tube stereo headphone
amplifier. Class A single-ended operation with constant current source cathode followers driving a pair of Combination core transformers using High grade
Grain Oriented Silicon Iron (M6) and
Mumetal (76% Nickel). This provides
ultra low distortion, exceptional bandwidth and transient response which is
maintained over the full dynamic range.
Selectable output impedance switches
ensure the correct match with your headphones. Noise and hum are undetectable
even at full volume which with most
headphones would be a level 4 times
louder than you could stand to listen to it
at.
FEATURES
♦ ALPS volume control, headphone
jack, and impedance switches are located at the front for ease of use.
♦ Removable power cord and on/off
switch are located at the rear as are
the high quality Gold/Teflon RCA input
jacks.
♦ Super low output impedance will drive
even the most stubborn headphones
while maintaining the correct frequency balance.
♦ Powder coated steel chassis is sealed
with no vents to let in dust, smoke, or
other contaminants including stray
RF. Stays new looking inside even after 20 years!
♦ Massively oversize power supply using
tube rectification and Ruby GOLD
caps offer bottomless power without
getting hot - in fact you can leave it
on 24hrs a day with no worries.
♦ In the Zen tradition, top grade inter-
nal parts are all hand point-to-point
wired with parts leads and no hookup
wire in the signal path.
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POWER CORD
The power cord is a standard IEC removable type with ground. You may substitute after market
“audiophile” power cords if you so choose.
FUSE
The fuse is located inside the IEC removable power cord jack on the back of the amplifier. To access it, remove the power cord and pry the little hidden door open. You will find the fuse holder
also contains a spare fuse. Use only 3 AMP fuses. We recommend using the SLOW BLOW type.
POWER SWITCH
The power switch is located on the rear of the amplifier. You can tell when the switch is on because the tubes will glow. There is no harm in leaving this unit on 24 hours a day if you so choose.
TUBE INSTALLATION
Do not power the amplifier up until you have installed all 4 tubes. The larger tube socket towards
the back is for the rectifier tube. We ship this amplifier with a 5Y3GT rectifier tube. It should
last for many years without problems. You may also substitute a 5AR4 rectifier or even a 5U4 rectifier tube. Each will slightly change the sound.
The remaining three sockets are for the smaller 6N1P tubes. A 6N1P is a dual triode. The one that
is located closest to the volume control in the front is set up as a buffer stage to drive the other
two 6N1P tubes. It has both left and right channel information on it. If you like to experiment
with tube rolling, this is the best tube to start with since it effects both channels at the same
time. The remaining two 6N1P tubes are configured one per channel, so the left tube is your left
channel and the right tube is your right channel.
You may substitute either a 6922 or 6DJ8 tube for the 6N1P if you want to, just make sure that
you make both channels the same.
INPUT/OUTPUT JACKS
The MLB uses a standard 1/4 “ stereo headphone jack for the output. It is located directly in front
of the input tube on the top of the amplifier. This is where you plug your headphones into. The
input jacks, located on the rear, are standard RCA type jacks. They are color coded, RED = RIGHT
channel and WHITE = LEFT channel. This is where you will plug your line level source, such as a CD
player, tuner, or phono-stage.
IMPEDANCE SELECTOR SWITCHES
The MLB uses TWO impedance selector switches, one per channel. These can be used while listening. They change the output impedance of the amplifier to operate either high or low impedance
headphones. Simply listen to your headphones both ways and choose which sounds best. Make
sure that you always switch both channels to the same position. Many of you will find that the
amplifier seems to have no problem driving your headphones in either position - this is normal.
Again, simply choose the position you like the sound and performance of the best.
VOLUME CONTROL
Located on the front of the amplifier to adjust the level. WARNING - this amplifier has lots of out-
put making it possible to damage your hearing if you turn the volume control too high. Most headphones are efficient enough that you’ll never get half way before it gets too loud. Also, because
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of the low distortion of headphones, it is very easy to listen TOO loud and not realize it. Please
keep this in mind because we don’t want you to damage your hearing.
OTHER STUFF
All of the things that apply to hi-end audio gear will apply to this amplifier as well. Use good interconnects between the amp and your source.
Like all audio gear, this unit will have to burn-in for several weeks before sounding it’s best. The
fastest way to achieve this is to play the unit at a normal volume for 5 hours and then turn it off
for at least 5 hours. Repeating this cycle 5 times will usually get you well on your way to a complete burn-in.
Headphones can be any impedance between 30 ohms and 600 ohms. We recommend if you’re just
starting out that you take your headphone amp to the store with you and listen to several pair of
headphones while you’re there. This way you can be certain of choosing a pair that you really
like.
SERVICE
There are no user serviceable parts inside. This amplifier runs with DC voltages of up to 500 volts.
Service by unauthorized or qualified persons could result in injury or death. Always refer any service questions or need to DECWARE. Even if you’ve purchased this unit second hand, we will still
service it at a very reasonable cost.
NON-USA MODELS (220-240 VOLT)
All information contained in this document applies to both USA (120) volt and non-USA (220/240)
volt models. Countries with higher voltages (250 or 260 volts) should consider using a voltage
transformer to reduce the voltage to at least 240 volts.
JAPAN
This amplifier will operate fine on 100 volts, so the USA model is recommended for JAPAN.
SHIPPING
Do not attempt to ship this amplifier without the proper factory foam packing container. If you do
not have one, you may purchase it from DECWARE for a minimal cost.
WARRANTY
The MLB, like all DECWARE amplifiers, comes with a lifetime warranty to the original owner
against defects in materials or workmanship. Tubes come with a 90 day warranty, even though
most will get many years of use out of them.
SUPPORT
Support for this product can be optained by calling us during business hours, or by viewing our web
site. There are support forums on our site that bring instant responses to your questions.
MANUFACTURED IN THE USA by
DECWARE / High Fidelity Engineering Co.
1202 N.E. Adams Street, Peoria IL 61603
(309) 671 2428 or (309) 672 1060 - fax line.
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SPECIFICATIONS
Size 6"W x 11"D x 6.5" H
Weight 13 lbs/120Volt or 14lbs/240Volt
Chassis Steel with grey powder coat finish
Consumption 70 watts
Input jacks Gold/Teflon RCA
Output jack Stereo 1/4 inch phono
Input impedance 100,000 ohms
Output Zo < 10 ohms
Transformer Type AC coupled, 1 per channel
Max Ratio 12:1+1+1
Trans Pri Z 10,000 ohms
Trans Sec Z 600/150/70 + 75 ohms
Impedance Range 30 ~ 600 ohms
Trans Max Power at 20 Hz 500mw
Frequency Response +/- 1/5dB 10Hz ~ 30kHz
Frequency Response +/- 3 dB 6Hz ~ 70kHz
Operating Modes Duel Lo/Hi Z
Max output into 32 ohms 4 V RMS (150mw)
Max output into 250 ohms 6 V RMS (120mw)
THD @ 1 V RMS / 1kHz 0.6 % ~ 1.0 % 250ohm HiZ/32 ohm LoZ
Noise @ 1 V RMS / 1kHz - 65dB
Operating Voltage USA 100~125 VAC 50/60 cycles
Operating Voltage World 220 ~ 250 VAC 50/60 cycles
Warranty Lifetime to original owner
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SCHEMATIC
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