Quantum Revolution vs. Soundtraxx Tsunami

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by Paul Turvill

Paul Turvill looks at the overall performance characteristics of the Quantum Revolution and the Soundtraxx Tsunami.

Introduction

Adding sound to a “silent” DCC model locomotive has never been easier, nor have there been more choices of quality sound decoders than are available today. Competition for aftermarket DCC sound has drawn several manufacturers into the fray, including Digitrax, QSI Solutions, Soundtraxx, and others. For most modelers the most difficult part of the conversion process is the dilemma of where and how to mount suitable speakers, especially in Diesel units whose shells are nearly filled with pot metal castings to add weight.

Since the “speaker dilemma” is essentially the same for any aftermarket installation, and varies greatly from model to model, this document leaves that problem to the reader, and will concentrate on the pros and cons of two front-runners in the DCC sound decoder aftermarket: the Quantum Revolution by QSI Solutions and the Soundtraxx, Tsunami. Both makes offer many variations of both steam and diesel units, and except for the specific “sound sets,” the following comments apply to both.

Decoder Specifics

The Tsunami decoder was the model TSU-1000 with sounds for the EMD 645 prime mover. This is a medium sized shrink-encapsulated unit equipped with a non-terminated “harness” of nine wires for motor and function connections, plus two more for a speaker, and a “pigtail” connected keep-alive capacitor. The Tsunami has a 16 Bit processor and the Revolution has co-processor technology incorporating a 16 bit and 8 bit processor. The Quantum Revolution was an “A” model, designed as a drop-in substitute for a standard decoder used in Atlas and many other popular makes of HO scale locomotives; it was supplied with connection tabs suitable for “push-on” connector blocks or soldering of existing or user-supplied wiring. The factory-installed firmware was designated 1050-431. The Revolution also came with a “pigtail” capacitor, and pre-installed but non-terminated speaker wires.

Evaluation Procedure

Using a model that came with a previously installed sound decoder, I first installed the Tsunami by simply disconnecting the factory installed unit and then connecting (soldering) the leads from the Tsunami to the appropriate connection points. I attached mating two-pin connectors to the Tsunami’s speaker leads and the existing speaker wires to facilitate the later changeover to the Revolution.

With the Tsunami installed, I then ran the test unit on my “test loop” consisting of a closed circuit of track on my main layout that consists of level straightaways, 30” and 32” curves, and a long 2% grade that starts on the level and then climbs upward through a 30” radius curve. This combination was selected because it allowed sufficiently varied conditions to evaluate running characteristics of both the “bobtail” configuration (no train), and pulling characteristics with trains of up to 25 typical HO freight cars.

After many hours of running, adjusting, tweaking, and just plain trial and error with the Tsunami, I completed my evaluation. I then swapped out the Tsunami and replaced it with the Revolution. Since I had left all of the surplus length of the Tsunami’s wires intact, it was a fairly simple chore to just snip them at the points that left enough length to connect to the Revolution. These leftover wires were then simply soldered to the appropriate tabs on the Revolution. I added the necessary two-prong connector to the Revolution’s speaker leads, and the installation was essentially complete.

The final stage was a similar series of running, adjustments, tweaking and trial and error to optimize and evaluate the Revolution over the same trackage and same conditions as was done with the Tsunami. During the “tweaking” mode of the evaluations, the Revolution’s ability to verbally read out the current value of any CV proved to be a true blessing. There never was any doubt as to the current setting, and the ability to confirm settings totally eliminated guesswork and the need to re-program a CV “just to be sure.”

Results: The Sound

To my ear, the sound from the two makes was comparable. There were differences, to be sure, but overall, the sounds from both said “This is a diesel locomotive,” and both decoders have sufficient range of volume and “mixing” capability to achieve the balance among the various operating sounds, both automatic and manually controlled, to please most modelers. I found the startup sequence of the Tsunami less flexible since it imposes a delayed response to the first throttle application while the engine “starts” and gets ready to go to work. The startup sequence on the Revolution (as with all QSI decoders) is manually controllable, so that the loco can be always “ready to go” even when the operator moves the throttle to speed step 1 for the first time in an operating session.

Notching on both units was good, and, again, is adjustable to suit the operator’s preferences. I left both units at the factory default in this respect, and wasn’t particularly bothered by notching effects in either one. The Revolution has a unique option that allows the user to establish his settings and then retain, lock in, those settings as the factory defaults.

The horn and bell selections were appropriate to the model, and both makes offer the means to customize these sounds for users who wish to further “personalize” their units.

As with virtually all, smaller scale (HO, N) models, the necessarily small speakers are probably the greatest barrier to “realistic” sound, especially in terms of lower (bass) frequencies. Both the Tsunami and the Revolution produce credible “model” sound given this limitation. I noticed no “tinnyness” and very little distortion from either unit, especially at mid-level volumes. Both units were capable of sound volumes considerably higher than the average modeler would want or need. I ran the Tsunami at about 60% of maximum, and preferred the Revolution at 50% or a little bit less.

When it came to “muting” the sound (F8), the Revolution provides more options: it permits the “muted” sound level to be set to a fraction of the “full” sound level, ranging from 0 to 100%. With the “mute” level (CV51.1) set to a value of 30 (maximum is 127), the unit “quiets down” to a level that is still perceptible, but not totally silent; this allows it to “fade” into the background when in tunnels, on hidden trackage, or just parked, so as to be audible but not interfere with other operations. By contrast, the Tsunami is either set at its maximum, or totally silent for the mute setting.

Performance: Lighting Effects

My test unit had only the two “standard” lights, a headlight and a reverse light, so I had little opportunity to compare many of the various special lighting effects offered by these decoders. However, even for these two lights, the Revolution is provides considerably more control than the Tsunami. While both units offer “dimming” of the head and reverse lights, dimming on the Tsunami requires a separate function key (I mapped this to F5 for testing), and the dimmed intensity is fixed at about 60% of the normal setting. Conversely, the Revolution provides automatic “Rule 17” dimming for those who want it, and both the maximum intensity and the dimmed intensity are continuously adjustable from 0 to 100% brightness.

Both of these decoders are compatible with either low-voltage incandescent or LED lights (my test unit used LEDs). The Tsunami has an “LED compensation mode” achieved by setting bit 7 (decimal 128) for any of its four lighting output CVs, while the Revolution handles this compensation by means of its various intensity control CVs. The Revolution has six lighting outputs and the Tsunami four.

Performance: Speed Control

The Tsunami includes six CVs that affect speed regulation (Back Electro-Motive Force, or BEMF): CV10, CV209, CV210, CV212, CV213 and CV214. At this stage, these CVs are not mentioned in the documentation that comes with the decoder. The Tsunami “Diesel Sound User’s Guide” discusses only the first four, explaining the experimental technique to improve performance. To find any information on CV213 and CV214, I had to refer to the “Technical Reference” manual, but other than acknowledging their existence, that manual gives no clue as to their intended (or expected) effect on speed regulation, even though I found through experimentation that both of these nearly undocumented CVs could greatly affect performance. I found the low speed performance to be fairly good with the factory default settings, but on my system, high speed performance “topped out” at a maximum of about 50 smph for about the last 25% of the speed range. (This was verified by running a speed profile with Railroad & Company’s TrainController software—see screen shot, below.)

Speed Curves for Tsunami optimized for low speed

By experimentally tweaking these CVs (including CV213 and CV214), I was eventually able to achieve a smooth transition from mid-range to top speed (about 58 smph), but in the process, I lost some noticeable capability of running smoothly at low speeds. The unit did not move at throttle settings below about speed step 7. The necessity to make a choice between optimized high-speed operation and optimized low-speed operation is a dilemma.

Speed Curves for Tsunami optimized for high speed

By contrast, the Revolution provides eight CVs (in the “PID” group) capable of optimizing speed control in each of four ranges: very low speeds, low speeds, medium speed, and high speed. While it is not a trivial process, optimization can be done individually by adjusting the pair of CVs for each speed range. Adjustments for one range have little or no effect on other ranges except for the “fringe” areas where the ranges meet or may slightly overlap. In general, I found it possible to achieve smooth operation from less than 1 smph (speed step 1) to about 58 smph at maximum throttle. In addition, there’s CV56.5, which permits the user to set the minimum BEMF to be applied when operating at very low speeds. With a range of 0-31, this setting can be used to compensate for “sticky” mechanisms or track work to prevent “stalls” at creep speeds.

Speed Curves for Revolution “A” optimized for all speeds

All of the above results were obtained with a “user loadable speed table” with a slightly faster rate of increase at the lower levels, and the low end (CV67) set to obtain approximately 1 smph at speed step 1 on a Digitrax system.

Customization and Other Features

Both the Tsunami and the Quantum Revolution represent state-of-the-art technology in model railroad control, and both offer considerable flexibility to the end user. Both permit a great deal of customization, including numerous choices for lighting, sound effects, and load and speed compensation.

In addition to the features discussed earlier, the Tsunami offers the user a selection of different air horn sounds, selectable by CV115 to an appropriate value. Otherwise, the user must be content with the sounds “built in” to the decoder as it comes from the factory.

By contrast, the Revolution user has a virtually unlimited choice of sounds and upgrade options if he wishes to purchase a Quantum Programmer. With the Programmer one can download the appropriate no-cost software (Q2Upgrade, and Quantum CV Manager) that offers one the ability to change, upgrade or customize the entire family of sounds for a given locomotive. Downloadable firmware for a variety of models is always available from the QSI Solutions Web site, and is easily user-installed. It is even possible to change a Revolution’s entire “personality” from one type of locomotive to another. In my own case, I have now successfully converted a pair of spare “diesel” Revolutions that are now installed in steam locomotives: one in an Athearn FEF 4-8-4, and another in an Athearn Challenger.

Conclusion

The ultimate choice, of course, between the Tsunami and the Revolution (or one of the other contenders in the DCC sound aftermarket), will be up to the user. I have read both positive and negative comments on most of the available offerings, ranging from valid criticism to more than a few based largely on one or two particularly good or disastrously bad experiences. In the long run, however, based on many hours of experimentation and personal operating experience, the Quantum Revolution is an ideal option for anyone looking for the best combination of flexibility, customization, and performance.