QSI Tips

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qsi_decoder_5971.jpgThis page is dedicated to the details of one particular DCC/Sound decoder, the QSI Quantum Aristo. QSI makes some HO sized decoders and just one model of a large scale decoder, the Quantum Aristo. However it is a really good one that seems to work just about anywhere. Nominally, it is "Plug-N-Play" decoder intended to work in the DCC socket of AristoCraft locomotives. However, it will also work in the sockets of some Bachmann locomotives as well. It also has an adaptor board that simulates the socket and converts the decoder to a screw connection version. When the decoder is plugged into one of these adaptor boards, it is called a "Quantum Magnum".

This is a full function DCC decoder with a 3 amp average motor capability and an excellent integrated sound system. It has been used on locos as large as an Aristo SD45 and many USA Trains locos without blowing up. It will also work in much smaller locos where it will physically fit. It will work on DC as well as DCC although on track powered DC it will shut down when the track voltage gets too low however there is a SuperCap kit for it that allows the sound to continue for a few seconds after loss of track power. QSI also makes a radio receiver that will plug into the decoder and accept commands from an Airwire transmitter so that it can also function under battery power.

There is just one model of this decoder used for both steam and diesel. Depending on who you order it from, it may come with a particular sound set pre-installed. The entire sound set and decoder parameters can be reloaded into the decoder at any time PROVIDED that the user has the Quantum programmer software and interface. Firmware upgrades can also be installed via the programmer. There is much more data in the sound set than just sound. For SOME locomotives, QSI has determined an optimal set of operational parameters that is included in the sound set so that the user doesn't have to tweak these after the fact.

This page will be by nature limited in scope to straight up DCC issues because I have no experience with it in DC or battery powered modes. I will also not try to repeat information that is in the manual except where I found it confusing. As of the creation date of this page, I have three of these puppies, all steam, one in a Bachmann Shay, one in a recent Aristo Pacific and one in an LGB 22232 0-4-0 switcher. A sample of the sound that the QSI makes can be found in this QuickTime video of the one in the Shay.

I felt that this decoder deserved it's own page just because it is so different than a more standard DCC decoder. There are many decoders that can just be described with a few specs, all the details follow standards. This is good, with most other decoders, an experienced DCC user doesn't even have to read the manual until it comes time to tweak some manufacturer specific Configuration Variable. The QSI decoder will work right out of the box as well but to get the most out of it, it needs some tweaking.

The decoder comes with minimal instructions for programming. You should download the ~250 page programming manual from the QSI web site if you want to make any changes at all.

This decoder is not yet completely bug free, some things don't seem to work quite right, but it can be made to work quite well with some simple work arounds or programming adjustments.


Operational Characteristics

From a DCC throttle, the QSI works pretty much like any other DCC decoder. It will respond to the throttle in a normal fashion except that it comes programmed with an acceleration and deceleration delay that comes along with it's default throttle mode. It's functions also respond differently depending on if it standing or moving. There are also some functions that change depending on what it was doing previously. All this can be a bit confusing at first blush, but you get used to it.

The 250 page instruction manual has the details of how the system works and how to best take advantage of the features of the decoder. This link is to the Nov 2010 version, 4.6.1. If they update the manual the link will probably break. A revised link can be found at the QSI by following the Q2 link and looking on the right of the page for the new link.

Sound. The decoder's sound responds in synchronism to throttle commands although the steam chuff can be controlled by a cam as well. If the chuff rate doesn't match the loco speed very well, it can be tweaked. The sound is fully digital and of very high quality with lots of voices available. For example, the cylinder cocks can be activated such that the cylinder blowdown will play, in sync, for 16 chuffs or to 12 smph, whichever comes first.

Lights. The lighting follows Rule 17 unless you change it. The lights will be dim unless the loco is moving in the direction of the light, when it will switch to bright. There are parameters for changing how dim the lights are, but the bright parameter seems to be set at max and does not appear to be user changeable. The lights ramp from dim to bright slowly so that it would not appear to be required to add resistors in series with incandescent bulbs. The decoder gives them time to adjust. The ramping is also a little easier on the bulbs than just being slammed on or off. The "dim" setting defaults to 32 (range of 0 to 255). For an incandescent bulb, this can be roughly equal to "off" but it works fine with LEDs.

BEMF. The decoder has back EMF capability that is enabled by default. The mode that is active is called RTC, or Regulated Throttle Control. This mode has loose BEMF coupling so that the locos used in this mode will consist fairly well without serious bucking. There are three other throttle modes as well but currently two of them are disabled due to some patent issue with Mike's Train House who claims a patent on some forms of BEMF control where there is clearly prior art. I expect that this issue will be resolved sometime, but it will take lawyers and courts to change it. The other available throttle mode is STC, or Standard Throttle Control. This essentially turns the BEMF off.

When in RTC, there are several BEMF parameters that can be adjusted to change the performance of the BEMF system. There appears to be a bug in the BEMF system so that in once case I had to turn it off, see the Odd Behaviors section below.

Speed Control. The decoder has the capability, by reading the BEMF signal, to determine the motor speed. If this is calibrated by measuring the actual locomotive speed, the loco can report its speed in miles per hour and it can use the actual speed to trigger some sounds. The speed can also be matched to the throttle setting such that 50% is also 50 smph.

Audio Feedback. Since this decoder has sound integrated, it can report, via a recorded voice, what it is doing or the results of programming. When you change a CV value in OPS mode, the voice will report the CV being changed and the value that it changed to. By entering a CV value into CV64, the voice will report the current value without changing it. This makes programming on a programming track unnecessary because the decoder can tell you what it knows by audio feedback.

Function Outputs. The QSI has only two native function outputs, F0f and F0r (white and yellow wire). These are all that are implemented in the Aristo PnP interface. There is or will be an accessory interface that adds more function outputs at extra cost. Since most of the extra function outputs that I use on other decoders go to controlling the sound system, the lack of these extra outputs on the QSI is not all that important because the sounds are already directly controlled by function keys. I generally don't like to wire smoke through a decoder anyway and things like the cab light and markers can be left on all the time.

If you really need more function outputs, then for $17 you can get a Digitrax or TCS function only decoder that provides 4 additional 250 mA functions with special effects.

Speed Matching. The QSI decoder has built in momentum, I think to allow the sound and motion to better coordinate. This complicates speed matching to other DCC equipped locos with other kinds of decoders some, but not a lot. The standard speed matching process applies. You can do this by programming on the main using whatever OPS mode programming method your DCC system allows. This method uses the "3 point" speed matching method which will work just fine for the vast majority of cases. I've never had to use the full 28 step table to speed match any locos well enough to consist nicely. If you want to do 28 step speed matching, use Decoder Pro in JMRI. Don't try to do it on a throttle.

  1. Place the locos on parallel tracks or one behind the other with some space between them on the same, preferably level, track.
  2. Initially set CV's 2 through 6 to zero on both locos.
  3. Set CV2 on both locos
  4. Put the locos in a consist. This makes it easier to control both their speeds at the same time.
  5. Run the throttle up to max and see which one is faster. If the locos are on the same track and the faster one is the rearmost one, run them in reverse so a gap opens between the locos.
  6. Set CV5 on the faster one to bring it down in speed to match the slower one.
  7. Keep adjusting the faster one to match the slower one at full throttle
  8. Then set half throttle and adjust CV6 to match them at half speed.
  9. Then set CV3 so that non-QSI equipped loco matches the speed up characteristic of the QSI equipped loco
  10. Do the same with CV4 for the slow down characteristic
  11. At this point, the locos should be matched well enough to run in a consist.


The QSI can be completely programmed from a full featured DCC system like a Digitrax Super Chief but it takes the special programming interface to change the sound file or update firmware. I don't have the programming interface yet so that there is little that I can say about it, BUT, there are some things I know.

Progrmming Interface and Software. The QSI software works in conjunction with a hardware interface. The software can be downloaded and some of it's functions used without the interface. The major function is to preview sound files see what you will get when you order it with a particular sound file. Sound files are also downloadable free. When a computer is connected via the programming interface to a decoder, all of the programming of CVs can be done via the software interface. This makes massive changes to the CVs much easier.

Macintosh Compatibly. The rub here is that the software is released ONLY for Windows. This is a problem for me because I don't have a Windows PC, my household is 100% Macintosh. However, there are three ways around this issue.

I expect that eventually, I'll buy the programming interface since I now have three of these puppies to support and I am sufficiently impressed with the QSI decoder to be inclined to buy more when I need both motor control and sound for a new installation.

DCC Throttle Programming. DCC decoders are usually programmed via CVs, or Configuration Variables. A CV is an 8 bit memory location in the decoder which is non-volatile. Once a CV is set, it stays that way until it is explicitly changed. The decoder uses the data stored in the CVs to define many of it's operating characteristics. Many of them are predefined in the NMRA standard and the QSI follows the standard.

There is a small range of CVs, 49 through 64, which are defined to be manufacturer specified. What these do is entirely dependent on who made the decoder and these are the only ones I'll be dealing with here.

There are only 16 of these CVs so that this tends to constrain what custom things a decoder can do without some kind of special tricks. QSI is REALLY tricky here, they have managed to expand these 16 locations into hundreds of CVs by the definition of two modifier CVs. CV49 is called the Primary Index or PI. It acts like a shift key with up to 256 values. CV50 is the Secondary Index or SI. It can also take on 256 values. With these two modifiers, the remaining 14 CVs could be expanded into hundreds of thousands of CVs but QSI has not applied these shift codes to the whole range. Some of them are defined using only the PI, some are defined with both the PI and SI, some are reserved for future use and some are not modified at all by the PI and SI. Still, there are more CVs available than you can shake a stick at although getting to some of them may require setting the values of THREE CVs to enter just one value.

When a CV is listed in the manual as CVxx.yy.zz this means that to get to it, CV49 must contain the value yy, CV50 must have the value of zz (if given) and the actual data to be entered goes into CVxx. This may seem pretty convoluted, but it is necessary to create spaces for all the data that is needed to customize the QSI decoder within the constraints of the NMRA specification.

Fortunately, while in OPS programming mode, the address and value of the CV that you THINK that you are programming is reported by voice. By entering the address of another CV into CV64, the decoder will report only the existing value of the CV with the current PI and SI that are in effect.

If you try to program a CV with an illegal or unimplemented value then the voice will report the CV number WITHOUT a value or not report anything at all. Then you know that the programming attempt didn't "take" and you need to figure out why it didn't work. In my experience, this usually comes from trying to stuff a value into the wrong CV or by using an illegal or unimplemented value to the correct CV.

QSI's programming interface and software make programming these special CV's much easier than doing it on a throttle. Also, JMRI is aware of the CV structure of QSI decoders and also makes CV programming of the manufacturer specific CV's much easier. JMRI will run on a PC, Mac or Linux.

Odd Behaviors and Warts

I've come across a few issues with the QSI, one I think is a bug, one was just unexpected and one is a drawing error.

BEMF Issue. When I installed a QSI into the LGB 0-4-0, it didn't work properly. Going forward, the loco would not stop when commanded to zero speed. It was just crawling along making a mild buzzing sound. If I interrupted the motion of the loco with my finger, it would stop until started again. It didn't do the same thing in reverse. It was clear that the BEMF system was bumping it along but it SHOULD have been expecting zero back EMF. Maybe it cannot detect the very low value of BEMF generated by this motor at that speed and it THOUGHT that the loco was actually stopped. All manner of playing with the BEMF parameters didn't help. I "fixed" it by enabling the STC mode where BEMF is turned off. Then the loco behaved fine. This loco doesn't need BEMF anyway. Someday there will probably be a firmware update to deal with this.

Headlight Operation. The manual indicated that the headlights should follow Rule 17 dimming. In this case, they were programmed to be on bright when moving in the appropriate direction and dim when standing or going in the other direction. My lights were "off" when they should have been dim. I didn't think too much of it until I changed the headlight on the LGB loco to an LED. THEN it was dim. The rear headlight was still a bulb and it was off, even in a very dark room, there was no visible light coming off the "dimmed" bulb. It occurred to me that the "dim" setting was not bright enough for the filament of the incandescent bulb to reach about 900°C where it would be hot enough to radiate in the visible spectrum. A quick check with an IR thermometer indicated that the bulb was slightly warm, but just not visible. I bumped the intensity of the rear headlight from the default of 32 to 64 and now it runs dim, as described in the manual. This is probably why the incandescent lights in the Pacific and Shay also appear to be off when they should be dim. The front LED on the LGB loco was actually brighter than I wanted in the "dim" mode so I turned it down to half.

Screw Terminal Labels. The optional screw terminal adaptor board has eight screw terminals that are identified by a stencil pattern printed on the board. These appear to be correct. However, as I read the diagram that comes with the decoder, the location of the blue wire and the headlight identification is incorrect. If you follow the documentation, the lights won't work because they will be connected to ground instead of the +common or blue wire.

Physical Size. This is physically a large decoder, primarily in the thickness dimension when the adaptor board is added. This is due to the length of the pins for the PnP socket and to the size of some of the components on the board itself. While the adaptor board can be cut off right next to the 12 pin header row to make it a little smaller, it is still pretty big. It can be a challenge to find room for this puppy in some constrained spaces.

Wish List

The QSI is a well featured decoder, but it still doesn't allow some of the customization that other decoders and sound systems do.

Bell Ring Rate. I'd like to be able to adjust the ring rate of the bell, there doesn't seem to be a way to do that now. The bell simulates a fairly fast automatic ringer. I'd like to slow it down AND to optionally make the ring rate somewhat random as if a bored fireman was pulling on the bell rope. With the aid of the programmer, it is possible to upload different bell sounds with different ring rates. Some sound profiles have multiple bell sounds. However, if a bell provided isn't what you want and you don't have a programmer, then you are SOL.

Automatic Start and Stop Signals. The Soundtraxx Sierra sound system can be configured to make some automatic whistle, bell and air release sounds when it starts and stops. The Phoenix P5 does similar automatic signals. The QSI has automatic modes for many of it's sounds, but not these. I'd like the option of setting it up similarly to the Sierra where it blows two toots when starting forward, three toots when starting in reverse, plays the bell up to a preset speed and then blows one toot at stop with an air release.

Whistle Sounds. If F2 is pressed momentarily, the system will play a short whistle toot. If F2 is held down longer, it will play an extended blast for as long as the button is held down. This works pretty well, but you have to be quick to get the short toot. The problem is that in some sound sets, the short toot sounds like it is coming from a different whistle than the longer ones, the 505 set is an example. In the 500 sound set, the short and long toots at least sound the same except for duration. This should be fixed.

RDC Sound files. The Budd RDC used a hydraulic torque converter transmission and a 225 hp diesel engine driving each truck. They sounded much different than a "regular" diesel locomotive because they don't "notch" like most diesel electric engines do. The engine speed ramps up, but not as fast at the RDC speed changes.

Goose Sound files. There isn't a gas-mechanical sound file available for the QSI, at least not yet.

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© 2009 George Schreyer
Created 11 Nov 08
Last Updated October 14, 2009