SoundBytes Transformer Hum



The SoundBytes Transformer Hum is a simple, fully self-contained sound module that plays a background hum reminiscent of an electrical transformer or substation.  Add some ambiance to your layout's electrical infrastructure!

Best played at a low, understated volume.


  • Integrated speaker & volume control
  • Easy to install and use
  • Powered from 5V to 24V
  • 20mA idle current, 80mA average draw while playing, 160mA maximum

Sound Samples

Transformer Hum

Electrical Connections

The SoundBytes module needs 5-24 volts of clean direct current (DC) power to operate.  Connect the white wire to GND to activate the sound.  Leave the white wire disconnected when not in use.

Red Wire = 5V to 24V

Black Wire = GND
White Wire = GND to activate

Note:  Please do not use old model railroad power packs as a DC supply.  These often produce large output spikes far in excess of their nameplate voltage ratings, are not suitable for powering modern electronics, and will damage SoundBytes modules.  Please read this article for more details.

The volume can be adjusted by using a small screwdriver to turn the white, square potentiometer on the PCB.

Here is an example showing the SoundBytes module connected to a toggle switch:


1.25"(L) x 1.25"(W) x 1.25"(H)


The complete gEDA design files are available on GitHub.


  • $19.00

  • 3 in stock

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News & Application Notes

SoundBytes Cicada Primer

The MesquiteBelt posted a great primer video on using the SoundBytes Cicada sound module. Although specific to the Cicada module, it applies equally well to the other SoundBytes modules as well.

SoundBytes on Burr Stewart’s BN Layout

Burr Stewart recently installed some SoundBytes Crossing Bells on his Seattle region Burlington Northern layout. Take a look at his operations and modeling!

Simple SoundBytes Switching

We’ve gotten the question a number of times about how to turn the SoundBytes modules on and off with a switch.  It’s actually really easy, but since the question gets asked, I figured I’d do a very quick write-up on it.

First of all, the module requires a clean DC power supply of between 5 and 24 volts.  (Note:  PLEASE do not use old toy train power packs for this.  They do not provide clean DC power, and it’s often far, far over the ratings of the module.  Please read this for more details.)  The positive side connects to the red wire, and negative / ground connects to the black wire.

To activate the sound player, the white wire needs to be electrically connected to the negative side of the power supply (the black wire).  You can do this in any number of ways: a single-pole switch between the white wire and the black wire (SPST or SPDT, either will work), or a push button between black and white wires, or if you want it to play continuously, just connect the black and white wires together permanently.   To stop the sound, the white wire should remain disconnected (meaning the switch is off or open).

Here’s a simple diagram showing how to wire it to a toggle switch:

Is the Substation on Your Layout Just Ho-Hum?

Make it really HUM with the new SoundBytes Transformer Hum module! See it in action at the St. Louis Railroad Prototype Modelers Meet, July 29-30, 2022.



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