hi I'm Eric wine Hoffer product
development engineer here at make have
you ever felt that the sound coming from
your portable audio device is a little
lackluster at best well in today's
episode of weekend projects we'll be
building the bass bump headphone amp by
Ross Hershberger and don't let the size
of this little amp fool you it'll
instantly provide you with clear sound
and punchy dynamics through any pair of
headphones or even a set of small
speakers build one and you'll
immediately notice the difference let's
take a quick look at one channel of the
schematic the audio signal enters the
circuit and splits into two branches a
high and low frequency we can adjust
these frequencies with the addition of a
potentiometer before their combined back
together the signal then enters the
lm386 amplifier chip this chip is
powered by a 9-volt battery and provides
an extra sound boost as it exits the
circuit this is a fairly complicated
build so give yourself the weekend to
work on it fortunately it's easy to
source the components since they are all
available at your local radio shack
you'll also need the following tools
[Music]
we will start the bill by preparing the
PCV which has two identical sections we
will use one for the right channel and
one for the left to keep track of
everything we'll label the board first
mark one side of the board are for right
and one L for left label the traces on
the soldering side of the board from 1
to 20 and then repeat for the component
side of the board keeping in mind that
the order of the numbers will be
reversed once the board is flipped over
then label the holes on the component
side of the board a through e beginning
with a in the center of the board and
moving outward toward the edge component
connections will be called out based on
this number and letter coordinate system
so make sure you follow it exactly
insert the socket for the amp chip as
shown make sure to orient the notch in
the socket body toward the top of the
board flip the board over and solder the
socket leaves to the traces next solder
the 100 microfarad and 220 micro farad
capacitors the 100 micro farad capacitor
will require a little creative wiring to
fit properly around the socket next
we'll add jumper wires the one on the
left will need to be routed around the
holes below it so we can add additional
components later now we can solder a
point 0 4 7 micro farad and 33 Pico
farad capacitor to the circuit board the
finished board will be packed with
components so sorry these caps a bit
above the PCB surface this allows them
to be moved around to make room for the
resistors that we'll be adding soon
before we add the resistors will solder
in a pair of 0.2 2 micro farad
capacitors as shown now it's time for
all the resistors there are a total of 8
resistors that you will be soldering to
the circuit board the project page has
detailed descriptions of all the
connections and component values some of
the components will live off the circuit
board will need to solder 14 wires to
the PCB to make all the connections
necessary for the circuit now we need to
make the input and output cables start
by cutting a 16 inch section off each
end of the headphone speaker extension
cord the plug section will be input
cable and the jack section will be
the output save the leftover cord for
making the charging cable for the
battery next strip the black outer
casing from the cutoff end of each cable
section and remove the inner foil trim
the ground wire and twist the strands
strip the insulation off of the tips of
each of the black and red wires and
twist the strands together then slip a
black rubber grommet over the cut end of
each cable section position the input
cable between the two holes at the upper
edge of the PCB with the red and black
wires pointing toward the center of the
board and secure the cable to the board
with a zip tied solder the red and black
wires of the input cable to the PCB each
section of the PCB has a length of gray
wire strip their free ends and solder
them to the ground wire now you can
fasten the output cable to the PCB in
the same manner as the input cable
solder the red wire of the output cable
to the right channel and the black to
the left channel each section of the PCB
has a length of brown wire just like the
gray wires trim them to length and
solder them to the output cables ground
wire now we can add the base controlled
potentiometers you might have to cut the
shafts of the potentiometers down so
that control knobs will fit nicely start
by marking the lugs with a sharpie to
make the assembly easier then connect
them to the PCB with six of the off
board wires that we soldered in place
earlier the last step is to add the
power input Jack pass the black and red
wires from the PCB through the mounting
hole at the lower right hand side and
solder them to the terminals of the
power jack that's it the circuit board
is ready to go
our base amp can run off the internal
9-volt battery so we need to make a
cable that connects that battery to the
power input jack
solder the red wire of the battery clip
to the center contact of the coaxial
plug and the black wire to the outer
contact the internal 9-volt battery can
be recharged from a standard 9-volt
battery charger but because it can't
easily be removed from the case will
recharge it through the plug soldered to
its
make a charger cable by using a leftover
piece of headphone cable and soldering a
power jack to one end and a battery snap
connector to the other because we'll be
using two battery snaps to make this
connection you need to solder black to
red and red to black on the second
battery snap connector to maintain
proper polarity now it's time to give
the amp a quick test insert the two
lm386 chips a rechargeable 9-volt
battery and connect it to your mp3
player and headphones you should hear
the audio through the headphones and be
able to increase the base of each
channel by turning the potentiometers
clockwise now all that's left to do is
install the finish circuit in the
enclosure carefully measure and Mark all
the holes that need to be made take your
time and measure twice you can find all
the specific locations mapped out on the
project page after drilling your holes
install all the components in the
project enclosure before you know it
you'll be bass boosting your way to
music nirvana the project page has
additional information on modifying a
project and how to build a USB power
cable to use when the battery needs a
recharge it's also a great place to
share your own build of a base bump
headphone amp head on over and see what
everyone is making