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One reason for an electrical modification (rather than muffling the speaker) is explained in this OGR thread from just last year.  Apparently the electronics will overheat and fail if powered by 18V AC.  As mentioned above a voltage converter should be considered irrespective of your volume control.  The following is from this OGR thread which may have a few more tidbits applicable to your situation:

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But specific to volume.  I believe, as suggested by others, you will achieve some level of volume control by using the Buck Converter module and adjusting the voltage going into the bell sound module.  My guess is as you lower the voltage below, say, 7V DC you will hear the volume drop.  Above 7V and the volume will be steady.  Then if you go down to maybe 4V DC it will just stop.

I'd try the above first.  If this does not give you the adjustability you want, then I think you have to open the sound module (see the photos from the first thread I linked).  Then you will need to install a component between the electronics and the actual speaker in the module to reduce/adjust the volume.  It's not that this would be expensive (less than $1 in part(s)) but it would involve opening up the module and possibly require some soldering...

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@stan2004 posted:

My guess is as you lower the voltage below, say, 7V DC you will hear the volume drop.  Above 7V and the volume will be steady.  Then if you go down to maybe 4V DC it will just stop..

I dropped mine to 5v DC per your recommendation on my original thread Stan . Any lower than that and it's stops as you have stated.

My speaker is under the layout. Even at 5v it's still fairly loud. I ended up muffling it with a laundry soap jug measuring cap and it's now at an acceptable level.

Having said that I also added an on/ off pushbutton for the speaker so I can shut it off completey as desired.

Last edited by RickO

Ok, good comments everyone.  Thanks!

Questions:  The signal (lights) and speaker are AC powered components.  The included instruction specifies 10-14VAC.  I get from a couple of you that converting the AC to DC for the speaker is ok.  How about the signal?  I also read that 18VAC will overheat the components (I am going to assume both the signal and the speaker).  Can I run them both on DC?  Has anybody done this?  I believe both the signal and speaker convert from AC to DC internally.  If this is true and you supply DC instead of AC, will this damage any of those internal converting components?

So per John H, you should be able to run the lights with DC.  Based on this OGR thread, you need to put DC+ on the red wire.  That is, for the technically curious, it appears the crossing lights PCB only has a single diode to convert AC to DC (vs. a 4-diode bridge-rectifier); hence you need to apply DC with the proper polarity.

mth ag-5200015 PCB for 30-11014 flasher

As for as volume control, as GRJ says, you can splice a variable resistor (aka potentiometer) into one of the 2 wires going to the speaker.  But let's be absolutely clear; the 2 wires going to the speaker are INSIDE the black chamber.  The 2 wires going to the black chamber itself are the external AC (or DC) power wires.  You cannot just splice in the potentiometer to an EXTERNAL power wire going to the chamber.  I believe discussion of muting the speaker with a simple on-off switch is referring to simply cutting power to the chamber (EXTERNAL wire).

So.  If your head isn't spinning yet, for the most flexible volume adjustment you need to open the chamber per the linked thread.  It will look like this picture from the other thread:

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Then splice in the potentiometer (GRJ gave a suggestion) to one of the 2 wires going to the speaker. 

To make matters more confusing, if the $6.60 (plus shipping) of the 100 Ohm potentiometer is too much buck-for-the-bang, you could use a 3-position toggle switch (aka SPDT ON-OFF-ON) to swap in a fixed resistor (more like 10 cents) and simply have low-OFF-high volume selection.

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  • mth ag-5200015 PCB for 30-11014 flasher
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Now that I think about it, volume adjustment comes up for other accessories... Mel's Diner comes to mind.  If you're lucky you might already have or stumble across a suitable inexpensive potentiometer; but as shown above it might be a $5 part (plus shipping). For example, let's say your accessory has an 8 Ohm speaker (very common in accessories).  If you simply add a 100 Ohm potentiometer between the electronics and the speaker, this will provide a volume reduction range of 0 dB (no reduction) to about 23 dB.  Everyone knows dB relates to sound, but very few know a 6 dB reduction if it hit them in the ear.   1 dB is about what you get when you add or subtract one bar on a TV volume bar meter.  I don't know how "annoying" the crossing bell is, but my guess is you're looking for a reduction of at least 10 dB.

volume adjustment using 3 position center off switch

Note that  with the potentiometer, you don't get "mute" capability with a potentiometer.   Of course you can add a brute-force on-off switch which is a hard mute.

Or, if willing to give up variable adjustment and live with, say, OFF-LOW-HIGH volume you can use a 3-position switch which gives you true MUTE capability in addition to 2 other volumes.  As illustrated above (by way of example), if you use a few low cost resistors, you can experiment and pick what you want for the low and high volumes.  As shown, the 3 toggle switch positions would be MUTE, 0 dB (original volume), 15 dB reduction.  Or choose MUTE and any combination of 2 other reductions.  You might even save a few bucks going this route.

I purposely skipped over the math of how dB reduction is calculated...involves logarithms and other eyes-glaze-over techno-babble.

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Fair enough.  If it was an 8 Ohm speaker that would give an adjustment range of 0 - 17 dB.  This is a case of "I'll know it when I hear it" as to whether you want 5 dB, 10 dB, 15 dB, whatever dB.  Plus, I think it depends on the sound itself.  A monotonous, repetitive, clanging bell might be more annoying than, well, just about anything!  After all, it is meant to get your attention!

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