Pre-Fitted Speakers

[thirdline]

Hi, if a loco already has a factory pre-fitted speaker like the latest Bachmann V2, do I assume correctly that all is required when fitting a 21 pin sound decoder is to detach the speaker and isolate the wires.
Probably a daft question but I thought it best to make sure before I start snipping.
Thanks,
Mick.

[Flashbang]

Technically Yes that's all that needs doing. But why??
You don't have to have sounds On They are turned On/Off by a button press.
If you're upgrading the speaker you of course will need to make in line joints to the two speaker wires from the decoder to the new speaker.

[centenary]

Hi, if a loco already has a factory pre-fitted speaker like the latest Bachmann V2, do I assume correctly that all is required when fitting a 21 pin sound decoder is to detach the speaker and isolate the wires.
Probably a daft question but I thought it best to make sure before I start snipping.
Thanks,
Mick.

Hmm, I dont really follow. If you are fitting a sound chip after purchase, why would you detach and isolate the pre installed speaker wires? If you dont want sound, save money and fit a non sound DCC chip and save yourself about 100 quid.

[SRman]

Why would you detach or isolate the existing speaker? If you plug a sound decoder in, then it should work straight away.


If the decoder has a speaker already attached, then yes, you would isolate one or other of the speakers. Was that the question?

[thirdline]

Ah, maybe I didn’t word this as well as I could have, the question was that when you buy a sound decoder it will most likely come with a speaker attached, if you detach the speaker from the decoder prior to fitting it in the loco is that all that’s required? or do the wires from the decoder need to be attached to the pre-fitted speaker?
Sorry for the confusion guys,
Mick.

[centenary]

Ah, maybe I didn’t word this as well as I could have, the question was that when you buy a sound decoder it will most likely come with a speaker attached, if you detach the speaker from the decoder prior to fitting it in the loco is that all that’s required? or do the wires from the decoder need to be attached to the pre-fitted speaker?
Sorry for the confusion guys,
Mick.

There's a couple of scenarios. The majority of locos dont come with a pre fitted speaker and no sound chip fitted although the numbers that do, are growing.

A loco that has a pre fitted speaker but no sound chip likely has the speaker wires already soldered to the loco's main board so when a sound plug is fitted, that's all that is needed. Alternatively, the speaker may be attached to the board via a small JST plug.

If either of the above is the case and the sound chip you buy comes with a speaker pre wired to it you could:
1, remove the speaker wires from the chip and just fit the chip on the board.
2, remove the pre fitted speaker and if the wires are attached to the board via a plug, simply unplug it. Attach the sound chip and speaker via the DCC chip socket.
3, You could wire both the pre fitted speaker and the sound chip supplier speaker together to give better sound. However, you'd need to know what the sound chip's speaker resistance is, the resistance of the supplied and pre fitted speakers are. Id say only do this if you know all the resistance values and, whether joining the speaker wires in parallel mean they remain within the resistance range of the sound chip.

[thirdline]

Thanks Centenary, that’s what I needed to know.
Cheers,
Mick.

[Richard08]

Be very careful wiring speakers in parallel, resistance is not the same as impedance, 5ohm resistance is not the same as 5ohm impedance. Resistance is a DC function, impedance function of AC and is derived from the reactance (inductance - capacitance) against resistance x COS fi (can't find the symbol on this keyboard). Speakers and the like are AC systems. It likely doesn't matter at model power levels, but try it on your hi-fi and the power transistors will blow (though usually they have thermal protection these days). Unless the speakers are a matched pair (i.e. exactly the same) one or the other may draw more current, unexpectedly more current, as it a sum of 1/R1+ 1/R2 et al. I may be being OTT, but then may not be.

[Flashbang]

A 21 pin MTC decoder uses pins 9 and 10 for speaker connections via the locos PCB. But some are sold with speaker wires soldered to the decoder which really defeats the idea of using all the 21 pins and the locos PCB!