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Tsunami™ Digital Sound Decoder - page 49 / 77





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Sound Programming

be loaded with any value between 0 and 255. Higher values will yield higher chuff rates for a given throttle setting. A typical synchronization rate may be computed as:

SPD CV Value = 115.9 X ——— DIA

X Gear Ratio

where SPD is the locomotive’s top speed in scale miles-per-hour at full throttle and DIA is the locomotive’s driver wheel diameter in scale inches, and Gear Ratio is the gear ratio for shays and other geared engines. For conventional steam engines, use a Gear Ratio = 1. The driver diameter can be easily measured with a scale ruler but remember to convert the measurement to scale inches.

If you don’t know your locomotive’s top speed, you can also estimate it and still get pretty good results. A good rule of thumb is to use 45 MPH for freight locomotives and 70 MPH for passenger engines.

Hints for Setting Engine Exhaust Chuff Rate Because most locomotives do not respond linearly (i.e., straight line) to the throttle settings, it can sometimes be difficult finding the magic auto-exhaust chuff rate setting that works across the locomotive’s full speed range. We have two procedures for setting the chuff rate that have worked well. The first method is easy to implement and produces good results that should satisfy all but the stodgiest of nitpickers. The second method takes more effort but produces more accurate results.

Method 1 Begin by setting the starting voltage (CV 2) such that the engine begins to barely move at speed step 1. Then increase the throttle setting until the engine is moving at 10-15 scale MPH. Then adjust CV 116 up or down until the chuff rate corresponds to approximately four chuffs per wheel revolution.

Method 2 This procedure uses the loadable speed curve to compensate for the locomotive’s non-linearities. Begin by setting CV 25 = 16, CV 29 = 18 (50 if you are using a long address- see Table A) and CV 116 to the value calculated from the formula above. Set your command station to use 28 speed-step mode. Set the throttle to speed step 1 and adjust the first entry in the speed table, CV 67 until the locomotive speed matches the chuff rate. Increase the throttle to speed step 2 and adjust the second entry in the speed table, CV 68 until the locomotive speed once again matches the chuff rate. Repeat this process until you have adjusted the locomotive speed across all 28 speed steps using CVs 67-94.

Exhaust and Rod Clank Volume Control

CV 131 controls the exhaust chuff volume while CV 135 controls the side rod

Tsunami Steam Sound User’s Guide

Page 46

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