A range of current Graham Farish N gauge diesel models now come DCC-Ready with 6-pin sockets and often with head/tail
lighting as standard. These models provide a basis for adding DCC Sound, although not straight-forward by any means, much
simpler than some of the older split-chassis models.
I'll describe here some of the activities required to convert these modern Farish diesels to DCC sound using CT SL75 or
SL76 decoders and CT sugar-cube speakers.
The decoder itself does not present too much trouble, but the speaker requires some careful planning as to where to
locate it to get the best results. The enclosure of the speaker is vital to get good quality and high volume sound, and
there are 2 approaches to achieving this... seal the speaker into the loco's body somewhere, making an enclosure that uses
shell of the loco, or perhaps the fuel tank... or, as the examples here use, modify the supplied speaker enclosure, shaping
it to fit the roof of the loco, and grind a recess into the loco chassis to seat the speaker. The latter is YouChoos'
preferred approach as it generally results in a neater finish, although does require tools and skill to do the milling.
The first step is to carefully disassemble the model - it must be totally disassembled leaving just the metal chassis
blocks. This is important since the milling process causes lots of metal dust, not to mention heat, which will damage
anything else still attached. Total disassembly also gives you a great opportunity to clean the model thoroughly and give
it a greasing/oiling where appropriate.
Take it apart methodically, making notes of where everything goes, as well as orientation. Mark the chassis with arrows
or other helpful notes, which will be useful later on when you attempt to put it all back together again!
Decide where you'll get the most depth out of the chassis for the speaker, and use a milling machine (or you could
use a Roto-Tool like a Dremel with a tungston carbide disk), to cut away enough space for the speaker. Take the chassis
down as thin as practically possible, but not so thin that the metal becomes a fragile wafer!
If possible, grind both halves of the chassis together, as you'll get a more consistent recess.
When you're done with the milling, neaten the surface up with a hand file, smoothing off the sharp edges, since
there will be wires crammed in which you wont want to risk being sheared.
You shouldn't need to grind any space for the decoder, as it will probably not be any thicker than the original
circuit board, but do consider where along the chassis the decoder will sit. Plan positions of everything as you go,
including where you will need to route any wiring.
Note that in all these examples it is normally necessary to remove the factory-fit circuit board entirely, or you
simply wont be able to fit the sound decoder and speaker in. In fact, it is useful to chop parts of this circuit board
up to reuse in your install!
The first parts to chop off are the holes where the screws attached the circuit board to the chassis... these are useful
because you can solder the pickup wires of the decoder (red and black) to them and screw them back onto the chassis! Alternatively,
use some small washers to achieve the same thing. YouChoos' prefers to use the circuit board holes because they are
already the perfect thickness to accept the original screws, so you get a good electrical connection for the pickups.
Chop the decoder's motor wires (orange and grey) fairly short and solder them directly to the motor terminals and reassemble part of the
chassis - enough to test that the motor works ok. You can use crocodile clips from track to each side of the chassis
and test through your normal DCC controller. Check that the motion goes in the correct direction, and if not, simply
reverse the orange and grey decoder wires around on the motor terminals.
Remember to always keep lose wires clear, and the decoder/speaker clear of the chassis to avoid short-circuits. Shorts
are very easy to let happen, and can destroy a decoder instantly!
If the motor appears to run ok, you can reassemble the whole chassis, perhaps even the bogies if it seems to make
sense. Lay some thin electrical tape across the top of the chassis where you intend to place the decoder, then some
thin double-sided tape, and stick the decoder into position, shortening red, black, orange and grey wires so there
is as little excess as possible.
Keep testing as you go along!
Next, let's place the speaker - initially without the enclosure attached. Insulate the speaker's recess on the chassis with
some thin electrical tape and check that the speaker fits in neatly. Bend the speaker's terminals out and up if
necessary, ensuring that they will not touch the chassis anywhere.
At this point you will probably need to tie up the lose decoder wires because you'll be testing the fitment of the
loco's shell on top of the chassis, so bundle them up and tape them down temporarily so that they do not get in
the way of the body shell.
The speaker enclosure will need to be shorted in height by a couple of mm, and also filed over the top to closely match
the body shell shape of the loco. Do this progressively, placing the enclosure losely on the speaker and checking
periodically if you've taken enough off by trying the loco's body shell. You will probably have to be quite
aggressive in how much you take off, but don't worry - the speaker still performs very well, with loud volume, even
with an enclosure a third the original height!
If you go too far with the shaping of the enclosure, and end up braking through the top of it, don't panic, as you
can often fix this by dribbling some liquid super-glue inside the enclosure to seal it up again - although wait until it is
dry before you continue the fitting process!
Once you are happy that the speaker and enclosure will go in, and the body will fit on correctly, super-glue the
speaker to enclosure. Do this by putting a small amount of super-glue round the base of the enclosure and spreading
it evening around with a fine-tipped tool. With the enclosure upside down, careful place the speaker onto it and
leave for a couple of minutes to dry. Do not use too much glue, or you risk getting some on the speaker itself, but
use enough that the seal goes right round.
Sometimes it may be necessary to file down some of the inside of the roof of the model, but be very wary of this, as it is very
easy to file too much and put a hole in the roof!
So, with speaker glued to enclosure, place it into the recess in the chassis, perhaps using some very thin double-sided
tape to encourage it to stay in position. Solder the decoder's speaker wires (brown on CT decoders) onto the speaker
terminals, shortening the wires to make it neat.
If you're not bothered about the factory-fit lights of the model, you are essentially done! Put the body shell
back on and do some testing. Check for motion, free-running and sound quality/volume. Any kind of crackling from
the sound would indicate that the speaker's enclosure is not totally sealed.
Please refer to the fitting guide on Re-using Factory-Fit Lights in Farish Diesels for instructions on how to
connect a hard-wired decoder to those lights.