A tidy example of 47323 Rover Group was acquired some years ago. The spartan chassis of these Lima models means a decent amount of space to fit circuit boards, LEDs and a speaker. I finally got round to adding these goodies as the Winter evenings fizzled out.

Although covered elsewhere, I felt there were enough detail differences here to make a new write-up worthwhile.

Approach

My choice of components was:

• Zimo sound decoder, following good experience with a class 25 - MX645 with sound project DigiDrive E Version 3
• Speaker to fit loco - Soundtraxx 28x28mm
• Express Models lighting kit - L47W

Before starting conversions, motor and gear train were inspected and found to be in excellent condition - it looked like this model had hardly been used! Gears were carefully cleaned of excess grease and given trial runs. I'd intended to replace the ringfield motor with a Modeltorque motor kit, but it wasn't needed - so a spare is now available for a future conversion.

The speaker fits into the fuel tank/battery space in place of the large steel weight. The weight was removed, and small holes drilled in the base to form a grille. Plenty of sound escapes through these holes but enough plastic remains to protect the speaker against dirt and damage from below. The aim is to form an air-tight rear enclosure using 1.5mm thick plasticard suitably sealed round its edges with white-tack (other glues are available).

When selecting a speaker, I try to find one with the lowest resonant frequency (f_o) that fits the available space. My initial choice of a 31mm round QSI HB122R turned out to be very slightly too wide to fit the tanks, so instead I plumped for a Soundtraxx 810131 28x28mm (f_o 310Hz). On this speaker, the circumference of the cone is almost flush with the frame, so to avoid distortion, thin strips of plasticard were glued onto the front edges of the frame to ensure the cone-edges cleared the bottom of the tanks.

The MX645 sound decoder is fixed to chassis using a small piece of double-sided sticky tape.

Lighting LEDs were then added to the body shell per Express Model's included instructions. Required modifications are straightforward; just a few cuts to remove parts of the cab plastic that would prevent a good fit. The lighting circuit board is fixed to the roof with a double-sided self-adhesive pad.

The weight lost (260g) by the removal of the steel block is more or less replaced by the combined weight of the speaker, additional electronics and a chunk of brass cut to fit the remaining space above the speaker enclosure (38l x 26w x 12h). As shown below, the brass weight is actually two pieces of 25.4 x 6.2mm glued together.

Wiring was completed using heat-shrink sleeving on all exposed joints. The motor RF suppression capacitor was also snipped per DCC best practice.

Results

Initial motor and sound tests were performed using the chassis alone - much easier to fault-find or modify without taking the body off again.

Sound output was surprisingly good for this small speaker - with remarkable (and loud!) engine 'grunt' - but sealing that speaker enclosure is crucial.

The lights can be programmed to work singly or in combination by setting the appropriate CV values. For my installation, changes from the default values are:

Finally, the body was carefully replaced, checking clearances in case the new wiring fouled the motor bogie. And I must say it looks and sounds the bees knees!