These were restored and
upgraded by me, they were the first
pair of Dittons which I performed
any upgrades to so I used them as a
reference for any more involved work
in the future. They came to me in
quite a mess, covered in torn
mahogany effect Fablon. They were to
be bi-wired and be fitted with
upgraded crossovers and internal
wiring too. The first step was to
remove all the Fablon, this wasn't
an easy task as over the years it
had stuck fast and risked tearing
the veneer away from the cabinets
too. Then to clean up the mess left
by the adhesive and clean and wax
the teak veneer, this was quite a
lucky break because the underlying
teak was near mint and barely faded
at all, having been covered for
years.
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|
The
modified crossovers, the
tracks had to be
modified to allow the
bi-wiring, edge
connectors removed
and connecting wires
soldered directly
through the boards |
The original
crossover is mounted on a quality
glass fibre PCB, which makes
upgrading the components relatively
easy, the entire thing is very
simple with just a second order
crossover for the tweeters and a
first order inductor low pass for
the bass. The original bell wire'
internal wiring and edge connectors
were removed, the track layout of
the board modified to accept the
bi-wiring configuration, the board
was then drilled to accept the
thicker wiring which would be
soldered straight to the tracks and
also the high frequency filter
capacitor was replaced with a higher
quality LCR polypropylene one - the
original was a generic bipolar
electrolytic and when tested had low
value and sky high ESR.
I decided to leave
the original inductors - they
measured well, would only be
handling a modest amount of power
and new inductors are difficult to
get in some of these sizes and would
bump the component cost up
considerably for little if any
audible gain. Besides, inductors are
merely coils of enamelled copper
wire, with the exception of being
damaged through overheating there's
very little which could possibly go
wrong with them.
At customer's
request I also added a Monacor
wirewound tweeter level control
which was attached to the rear of
the box, the cut-out for speaker
connection plate was then enlarged
for the new parts, everything
soldered together and the whole
thing resealed (these are by nature
a sealed box, they don't take kindly
to air leaks). the reason for the
tweeter level control was two-fold -
firstly, the original Ditton
tweeters proved very fragile and
many have been replaced over time,
these were no different - the
replacement tweeters just don't
match as well as the original ones
did but genuine pairs of
replacements are hard to find and
expensive.
Secondly, the
speakers were to be bi-amped on a
small pair of single ended valve
stereo amplifiers, the tweeter
control enables some fine matching
of sound levels if the sensitivities
of the amplifiers don't match
perfectly. The tweeter controls are
merely a wirewound potentiometer
which forms a potential divider
which lets less voltage to the
tweeter as you turn it down, as a
result it has to sink a lot of power
and not really recommended for use
on large speakers if you wanted to
play them at high volumes for
prolonged periods - regardless of
the power rating on the box. Here
however, they worked well and
enabled the tweeters to match to the
bass units much better than before.
The 'C' covers for the drones were a
creative idea on my side and just a
small sheet of laminate attached to
the cone, bonded with soft adhesive
to prevent any vibration problems.
The original cones had become very,
very tatty. Even the driver frames
were coloured black, the end result
being a very smart pair of speakers.
All in all a great deal of work but
nice to see something which looked
so sad end up looking and sounding
so much better.
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 |
|
Front
view of the completed
speakers, the drones
were covered with
laminate |
Rear
view of the completed
speakers, tweeter level
controls are in the
centre |
