Hello All,
I’ve converted a number of Bachmann GP40s from DC to DCC- -all non-sound- -and re-motored them in the process while standardizing the decoders.
First, I would remove the shells and see what you are dealing with.
Are they DCC ready?
Do they have LEDs installed on the Original Equipment Manufacturer’s (OEM) Printed Circuit Board (PCB)?
I have four (4) GP40s that always run in a consist.
For ease of speed matching I used all the same motors without flywheels, Digitrax DH 166 decoders, and PX 108 Power Extenders; Energy Storage Device (AKA Keep Alive).
Some were DCC ready while others had OEM DCC PCBs. I removed all the boards and hardwired the decoders while adding LED lighting.
Even with motors without flywheels, there’s little room under the shell to mount a speaker.
The cavities for the flywheels, above the drive train, could possibly accommodate small speakers running in parallel.
Another option would be to mill out the weight in the gas tank to mount a speaker.
Bachmann makes fuel tank covers with holes drilled in the bottom for sound. These are held in place by screws that you would have to drill and tap into the weight.
Or, you could drill holes in the existing press-fit covers.
As far as decoder choice I’ve had great experiences with Digitrax non-sound decoders.
I am waiting on delivery of a Digitrax sound decoder for a current upgrade. I’ve been told there is a delay due to a chip shortage.
On a side note, I have read that the speakers Digitrax uses are sub-par and replacing them with Scale Sound Systems speaker(s) is a big improvement.
Keep the questions coming, let us know of your progress and as always…
Hope this helps.