Saturday, December 11, 2010

A diy task: Refurbish a subwoofer unit

Though this task was performed and completed
in June 2010, it is only now that I could put
this as a blog entry( I mean diary entry)
The dismantle of the subwoofer was a nerve
wrecking event at the beginning, as most of the
circuits are placed at the bottom of the cabinet
and have to be removed in parts, but when I
got a hang of it, I picked up the momentum
to proceed at a faster pace. The several
minor tasks include removing dust from the
components, after I had removed the cover from
underneath the subwoofer unit as it's one
of down firing design. The unit a NEC
subwoofer of the 1970s period, definitely
needed a change of capacitors to the power
supply section, I have to decide if the
original specifications be changed to suit
the type of sound of today or retain the
same signature sound of that period.

Since this subwoofer is part of a pair
(I've 2 units of the same) and to be used
as a stereo pair after the refurbishment,
so I followed back the same component
change as the other earlier acquired
unit but previously used in a mono
configuration. The handiwork was pretty
tedious, as it required dexterity of both
hands, magnifying glasses, and a strong
light source to enable me to see what
I'm doing! And yes, even before the change
of the electronic components, the woofer
cones were worked on, the rubberised(not
rubber but of another material that akin
to rubber like feel) surrounds needed a
change, and my friend Uncle Chew a design
engineer supplied me with a glue that
do not harden with age, and one of several
methods to change the surround. I finally
incorporated some of his method with that
of my own, to get the job done.

The 12" driver I discovered was a JBL
driver with a pressed metal chassis and
not the cast iron chassis frame that JBL
enthusiasts liked so much. Anyway, after
the surround was replaced and double
checked for correct alignment, the new
electronic components were replaced and
the circuit assembly put back in place, and
left to stand for a short while before it's
incorporated into the multi subwoofer
system that I've been using all this while,
and then the final test, the powering up.
This is always the nervous part of any
redo of the system's component units!
The reality test!

All went well and the usual thoughts about
the unit to go thru the customary running in
for the new driver surround and electronic
components change, which I reckoned needed
a few hundred hours. Sure enough the sound
did change, but very subtle indeed! A couple
of months had passed since June! The sound
remained the same, more or less. So a simple
check on the tuning sufficed, and it's music
again! A word of caution though, those who
are diy challenged in this area, should not
attempt this without proper supervision from
the learned hifi & diy gurus.

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