Digitrax's New SDH164D Sound Decoder

Digitrax Products
Digitrax Custom Sounds
Sound Products

Norm installs and takes you through the preliminaries of this new Digitrax sound offering.

Digitrax SDH164D

by Norm Stenzel

Digitrax has just added a moderately priced HO sound/ motor and function decoder to their sound decoder lineup. The SDH164D is about the same size as a standard HO non-sound decoder. It comes with a standard 9-wire harness connected to the decoder with a 9 pin JST connector for rail, motor, and F0 – F2 connections. At the opposite end of the decoder there is a second harness with the speaker, 330-uF capacitor and the wires for F3–F4 as well as a wire for a cam input.

The decoder itself should fit in almost any HO diesel or steam locomotive. While it comes with a 28 mm 32-ohm speaker, I have successfully used a TDS Mini-Oval 8 ohm speaker with it with very good results.

One of the really neat things about the SDH164D and Digitrax sound decoders in general, is that you can download new sound schemes off of the Digitrax website to the decoder using the Digitrax PR3 and Soundloader software. These sound schemes use regular WAV files for the individual sounds so it is possible for you to record your own sounds and load them into the decoder. Of course these files would need to be edited to work properly using any one of the many WAV editing programs out there. Here is a link to a freeware version of Wavepad.

The SDH164D specifications

The motor drive has the same FX3 features as the Digitrax non-sound series of decoders.

The SDH164D comes from the factory with a combination of a generic steam (default) and generic Diesel sound schemes loaded. These are selected using CV60 ( 0=Steam Scheme and 1=Diesel Scheme ).

The Steam Scheme has the Chuff, Bell, Whistle, Compressor, Brake squeal, Coupler Clank and other random Air sounds.

The Diesel scheme has the Prime Mover, Horn, Bell, Compressor, Dynamic Brake, Brake Squeal and various Air release sounds.

Generic Steam Scheme

This decoder is nearly the same size as a conventional HO non-sound decoder so installing the decoder itself is the same as a conventional decoder. The speaker is usually the challenge in any sound installation. In this case I used the standard 28 mm round 32-ohm speaker that Digitrax includes with all of their HO sound decoders. (This speaker fits perfectly in the TDS 1.1 Round Enclosure). Since I already had a brass HO USRA 0-8-0 with a DH163D installed, it was a simple job to simply unplug the JST harness from the old decoder and plug the harness into the 9-pin JST socket on the SDH164D. The speaker snapped into the TDS 1.1 Round Enclosure. Before mounting the speaker into the tender, I drilled a few holes in the tender floor for the sound to come through. I then used double stick foam tape to mount the decoder, speaker, and capacitor in the tender. This is a fairly small tender but everything fit without much trouble.

The loco ran smoothly through the entire speed range. The auto-chuff sound was not anywhere close to being in sync with the driver rotation but this was fixed using CV133 (Driver Diameter in scale inches) and CV134 (Steam Gear Ratio Trim). This takes a little trial and error to get set correctly.

At slow speeds the chuff sounds OK but as you accelerate it becomes more like a machine gun than a chuff. Whistle and bell again are OK. The compressor comes on randomly as do some other steam and air sounds. One irritating thing is that when you bring the loco to a stop, there is a large steam or air release, which is OK except that it does it twice!

Master volume is set using CV58. Individual volumes can be set for Chuff CV140, Bell CV141, Whistle CV142, Time Scattered air effects CV143, and Misc volumes CV145.

Generic Diesel Scheme

Again I had an HO Athearn F7A that already had a DH163D installed. I unplugged the old decoder and plugged the SDH164D into the existing harness. The 28 mm speaker with the TDS 1.1 enclosure fit in the rear of the shell. I mounted it to the shell facing down using double stick foam tape. Make sure that the speaker and enclosure don’t touch the sides of the shell or it might cause it to rattle.

The SDH164D defaults to the Steam sound scheme so you have to change the value in CV60 to 1 to activate the Diesel sound scheme.

The loco ran smoothly through the entire speed range. The diesel prime mover (SD38-2) went from an idle to about notch 3 in one step and then increased in rpm as the loco accelerated. The 5-chime horn blows as long as the F2 button is pressed. If you just touch the horn button you get a short toot so horn signals are possible. If you press F10 a grade crossing horn signal will play 2 longs a short and a long. F2 turns the bell on and off.

Of the two sound schemes that come preloaded in the decoder, I like the Diesel scheme the best. While it is not up to the standards set by the higher priced sound decoders, it is acceptable for the less critical sound enthusiast.

Changing the Sounds

As I said earlier, one of the neat things about this decoder is how easy it is to modify the sound schemes and change individual sounds. I downloaded the Generic Steam/Diesel sound scheme from the Digitrax Sound Depot website.

Using the Digitrax Soundloader software (also available for free download from the Digitrax website) and a Digitrax PR3 Programmer, I was able to replace the chuff sounds with some recordings that I had edited using WAVEPAD (also available for free off the Digitrax website). I also changed a few of the other sounds in the scheme as well. The result was a Steam sound scheme that has good chuff sounds through the entire speed range. The file that I came up with is available for download from Tony’s Digitrax Custom Sounds page.

The main point I am trying to make is that it is not rocket science to come up with your own sounds to enhance the enjoyment of having sound in your locomotive. The possibilities are endless. Everything from different and unique engine sounds to conductors calling out station stops.

At a list price of $49.95 the Digitrax SDH164D may be just what the doctor ordered for someone that does not want to break the bank while equipping a small fleet with sound.