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Micro DCC Sound Decoder

Application Notes


Last Updated 181028


ZIMO has recently released a new decoder format that is worth a dedicated page to collect my notes on specifications and applications.

This is a new format in the decoder market and concept you might find appealing!

History and Concept
I shopped the concept of this format around for several years but never found an audience.

I met Mr. Peter Ziegler, owner and founder of ZIMO ELEKTRONIK, GmbH, for the first time at the NMRA National Convention in Indianapolis, IN in 2016.  We discussed many things DCC and I pitched my concept for a N Scale sound decoder based on my years of experience as an engineer, model railroader, and DCC professional.  Mr. Ziegler looked at the idea and replied, "So you want a MX649 laid out end to end".  

He got it.  The concept of the MX660 was born.

To be sure it is said, the concept was simple.  I decided a really good DCC sound decoder for N Scale installations should have these characteristics:

- As thin and short as technologically possible 
- Absolute maximum width of 9.5mm (the width of an Atlas or Kato narrow hood diesel frame)
- Minimum of 6 function outputs (F/R headlight, L/R ditchlights, plus two for additional options)
- All functions should be designed for use with 3.2Vf LEDs so no need for external resistors
- Each function should have a convenient point to connect the positive wire for each LED so you don't have to bundle together a big wad of wires to splice into a single common
- A convenient point to connect an external stay-alive capacitor if desired
- All connections should be conveniently located on the edge of the board
- One side of the decoder should be perfectly flat and free of components

Regarding the last characteristic, I want to take a moment to explain my rationale for this because I think it is the crux of the matter and defining characteristic of this new decoder format.

It is my opinion that there will never be a manufacturer willing to produce a drop-in board style decoder to fit every model of N Scale locomotive chassis.  It's just not practical.  I look at my inventory of N Scale drop-ins and shudder when I think of how much it would cost to carry inventory of equivalent sound decoder.  I wouldn't even bother to calculate the expense incurred by a manufacturer.

It is also my opinion that if I have a decoder that is thin and flat on one side, I can mill the top of any frame flat (down to the top of the motor cradle in most cases) and make a perfect place for a decoder.  I can manage power pick-up using OEM equipment or SBS4DCC 0-80 Ring Terminals, I can get two wires from the motor easy enough, and I can manage lighting with SMD LEDS in a hundred different ways.

Finally, it is my opinion that nearly every N Scale diesel frame has a shelf over the rear truck or space in the cab to fit a SBS4DCC Sugar Cube Speaker.  If the decoder is about the same length as the motor and flywheels I don't encroach on that space over the rear truck the way a long thin decoder or short fat decoder does. Now I have ample space for a SBS4DCC "Sugar Cube" Speaker 9x16mm 8 ohm .7 watt w/ Double Deep Sound Chamber even if I have to mill the rear shelf down a bit too.

Now I can make an N Scale diesel GROWL....


ZIMO MX660 Micro DCC Sound Decoder

Universal Board-style Hardwire with Large Solder Pads

ZIMO Elektronik... World Class Motor Control... Exceptional Value...

ZIMO Sound Decoders are equipped with 6 independent sound channels, 1.1W sinus audio output at 11 kHz or 22 kHz depending on sound sample and 32 Mbit memory

ZIMO sound decoder offers an innovative concept for sound adjustment and optimization, which makes these procedures particularly simple for the user. The user can produce usable sound even without a computer or detailed configuration variable settings.

ZIMO sound decoders also offer all of the world class functions of our non-sound decoders: silent drive selectable between 20 or 40 kHz, adjustable BEMF, special settings for coreless motors, optional kph or mph speed control, constant stopping distance, HLU, ABC, advanced uncoupling functions, smart stopping (prevents stops on dirty track sections), updatable firmware, and RailCom.

ZIMO MX660 DCC Decoders offer the following features:

The MX660 is the universal board-style hardwire "micro model" for N scale sound in the ZIMO decoder range.  The MX660 is essentially the MX649 laid out flat with absolutely nothing on one side of the circuit board to allow easy mounting against any surface.  

This revolutionary new format is perfectly suited for N scale narrow hood diesels and other applications where height and width are limiting factors.  The board-style format is only 9.6mm wide and 2.5mm thick and is blank on one side.  It features a robust 0.8A motor circuit, 1W amp, 6 function outputs with unique constant current design, and connections for external energy storage, especially important for uninterrupted sound.  The large solder pads make it easy to terminate hardwired connections from the track pickup, motor, and lighting functions.  As with all ZIMO sound decoders, the MX660 features an on-board energy storage capacitor and direct connections for additional off-board energy storage capacitors for the sound processor to minimize interruptions in playback caused by poor power pickup.  Best of all, the function outputs utilize a revolutionary design that eliminates the need for external resistors making it perfect for use with typical 3.2Vf LED's.  The on-board capacitor and output design eliminate the need for additional components that consume valuable space.

The MX660 is the perfect micro sound decoder for narrow hood diesels because it is the thinnest sound decoder on the market today, measuring just 2.5mm tall.  The footprint is so compact, it fits easily into almost any Athearn, Atlas, Fox Valley, Intermountain, Kato or other narrow hood N scale diesel.  The MX660 will be perfect for compact HO scale models as well.

Decoder Formats:
MX660 - Universal Board-style Hardwire with Large Solder Pads

Feature Summary:

  • 14, 28, 128 speed steps
  • 3-way adjustable back-EMF
  • Selectable frequency for noiseless operation
  • For all DC motors including coreless
  • 3-point or 28-step speed table
  • 5 digit addressing
  • All US lighting effects with programmable timing and dimming
  • Free mapping, NMRA mapping or Swiss mapping function control
  • NMRA bidirectional communication (RailCom)
  • Short circuit protection
  • Thermal protection
  • Reliable overload protection
  • User updateable firmware
  • Editable and updatable sound files


ZIMO Features and Characteristics:

  • Conforms to applicable NMRA DCC Standards and Recommended Practices.
  • Address range from 1 ... 10239, consist range 1 ... 127; Functions controlled by main or consist address.
  • 14, 28 or 128 External Speed Steps, 256 or 1024 Internal Speed Step resolution for incredibly smooth motor control.
  • 3-point adjustable speed curve (CVs #2, 5, 6) or fully programmable 28-step speed table (CV #67 - 94).
  • Top speed (CV #5) can be used even when the speed table is used (CV #67 - 94), which means that all entered table values will be reduced automatically (i.e. to 80% if CV #5 holds a value of 200 instead of 252).
  • Switching Mode button function - Selectively switches to low speed and/or reduces or even removes programmed momentum.
  • Multiple CV sets, predefined or self-defined: by storing more than one CV set, a locomotive can quickly and easily be changed for various duties that require different CV settings (i.e. single locomotive or consist, layout at home or club etc.)
  • Supports Operations Mode (Program On Main) and Service Mode (Program Track) CV Programming.
  • Special programming mode called "Pseudo Programming" for Digitrax, Lokmouse-2 and other systems with only 2-digit display (up to 99).
  • Hard reset with CV #8 = 8; Optional hard reset to Alternate CV Set or sound project with CV #8 = 0.
  • Automatically recognizes and switches between the MOTOROLA and DCC protocols.
  • Operates with standard DC analog power packs, PWM power packs, and DC power supply. Motor regulation and momentum are also available in analog operation.
  • AC analog operation with Marklin transformers.  ZIMO decoders recognize the power surge that initiates a direction change.
  • User Updatable - Install the latest firmware yourself, in minutes, at no charge and without opening the locomotive. All ZIMO decoders come with this feature (including function and accessory decoders).  The new firmware is always available at no charge from the ZIMO or ZIMODCC web site. (Requires MX10, MXULFA, or other device)

ZIMO Safety Features:

  • Reliable high voltage protection and short circuit protection for motor and function outputs.
  • Thermal protection (100 - 120 C), shuts decoder down and notifies user with flashing headlights.
  • Models available for use with track voltage up to 35 V (MX644, MX699).

ZIMO Motor Control Features:

  • ZIMO Silent Drive motor control with Self-Optimization and numerous settings for manual optimization:
    • PID parameters
    • Reduce or cut regulation
    • Reduce or cut regulation above defined speed
    • Modify EMF sampling rate.
  • Realistic momentum:
    • Standard momentum (CV #3 and 4)
    • ZIMO exponential (nonlinear) momentum for extremely prototypical acceleration and deceleration
    • ZIMO adaptive acceleration to prevent startup jolt
  • High frequency Silent Drive motor control, selectable between 20 or 40 kHz, suitable for use with:
    • Standard DC motors
    • Coreless motors (Faulhaber, Maxxon...)
    • Difficult cases, such as the round Fleischmann motor
    • Old motors requiring low frequency 30 - 150 Hz
    • C-Sinus and SoftDrive motors as found in Marklin/Trix locos
  • The Self-Optimization feature of the decoder automatically tunes the motor control parameters of the decoder to the locomotive.
  • Designed to startup at extremely low threshold voltage.
  • Adjustable compensation for gear backlash during direction changes to eliminate startup jolt.
  • Mph or km/h speed control. Each speed step (1 - 128) is interpreted as 0.5 mph, 1 mph or 2 mph (for high speed trains). All locomotives on the layout are adjusted by means of a semi-automatic calibration section (i.e. 160 scale-yards = 72.83 on the layout). In operation, the speed is kept as exact as possible by continuously recalculating and readjusting it.
  • Special circuitry to prevent interference from capacitors, choke coils, which are often found on motors.  In some cases removal of these components may still be beneficial (See Decoder Manual).
  • Uninterrupted operation (no stalling, stopping and new startup) during continuity interruptions of up to 1 second.  All current models of ZIMO decoders have Common (+) and Ground (-) pads available for adding external capacitors.  Many ZIMO decoders have special circuitry for adding external capacitors (SPEIKOMP, SPEIGOMP) which minimizes programming interference.
  • Uninterrupted operation on dead track sections. The decoder firmware prevents the loco from stopping when track power is lost, even while the loco is coming to a scheduled stop. This ensures that the loco can start up again even after the capacitors dissipated the stored electricity.  Note: Requires external energy storage module MXSPEIK or MXSPEIG, other similar products or self-made modules connected to the decoder.

ZIMO Function and Function Output Features:

  • 4-15 Normal function outputs and logic-level outputs, depending on decoder type.
  • 2-4 Low voltage 5.0V servo outputs, depending on decoder type.
  • SUSI interface for the connection of other external modules, most often sound modules.
  • NMRA function mapping.
  • ZIMO Free Function Mapping procedure (CV #61=98) enables mapping of any output to any function key, directional or non-directional, which is not possible with NMRA function mapping.
  • ZIMO Swiss Function Mapping (CV #61=...) for special cases such as direction dependent taillights and cab light in Swiss engines.
  • Numerous special effects:
    • Soft start for function outputs
    • Function output dimming
    • Function dependent low/high beam
    • Adjustable flasher
    • Stop light logic
    • Output time-out function
    • Firebox Flicker
    • Speed and load dependent smoke generation and fan control
  • All US lighting effects
    • Mars Light
    • Rotary Beacon
    • Strobe and Double Strobe
    • Gyra Light
    • Ditch Light - Type I and II
  • Variable cycle times and minimum dim values.
  • Special CVs for automatic uncoupling (aka The ZIMO Coupler Waltz).  After pressing the function key defined for this action, the loco backs up a few millimeters to unload the couplers then actuates the uncoupler and moves forward away from the train. The distance the loco backs-up and moves forward as well as the loco speed step is definable with CVs.

Note: On some decoders, the same function outputs can be used as either logic-level, servo or SUSI outputs.

ZIMO Common Function Outputs (a.k.a. Logic Level Outputs):

The common function output, also called a "Logic Level" output or "unamplified" output, refers to the voltage level at the terminal (0V for "off", 5V for "on").  The funtion output has an internal protection resistor equal to 10K Ohms resulting in 0.5 mA maximum available output current.

The use of the common function outputs is determined with CV settings: 

CV # 124:

  • Bit 7 = 0 -> SUSI 
  • Bit 7 = 1 -> Logic Level 

CV's # 181, 182

  • If set, the common function outputs are used for servo control.

Logic Level Outputs of [C] and [D] Types: 

In all decoders with 21-pin "MTC" interface (either a [C] - type or a [D] - type, e.g. MX634C MX634D or MX644C); the two variations differ in the execution of function outputs FA3 and FA4:

  • "D" - Outputs FA3 and FA4 are "normal" amplified outputs
  • "C" - Outputs FA3 and FA4 are "logic level" outputs

Logic-level outputs can power one LED or any other load by using an external amplifier (i.e. M4000Z)."Logic Level" outputs can be amplified by adding the ZIMO M4000Z Logic Level Function Amplifier or similar devices.

CAUTION: "Logic Level" outputs are NOT active in the default configuration of the decoder because they use the same ports as the SUSI interface (clock and data) as well as the servo-control lines.

ZIMO Train Control and Feedback Features:

  • DC braking distance, ABC (stopping on asymmetrical DCC signal), Marklin braking section,
  • ZIMO "signal dependent train control" (HLU) with speed limits in 5 steps and "stop before red signal",
  • ZIMO loco number recognition only with ZIMO DCC system and ZIMO track section modules,
  • Constant braking with two variations:
    • Always start braking immediately
    • When speed is low, stop in same place
  • RailCom - bidirectional communication hardware is found in all ZIMO decoders:
    • km/h feedback
    • CV "on-the-main" read-out and confirmed programming
    • RailCom address feedback
    • Many more RailCom applications in future software releases

RailCom is a Trade Mark of Lenz GmbH

ZIMO Sound Features:

  • ZIMO sound decoders are equipped with 6 independent sound channels, 1 to 3W sinus audio output at 11 kHz or 22 kHz depending on sound sample and 32 Mbit memory.
  • ZIMO sound decoders use digital audio amplifiers supplied with 5V from a regulated power supply.  The sound produced from this solution is not influenced by fluctuations in the power supply and is fully available on analog DC systems of over 5V.
  • A sound-memory of 32 Mb corresponds to a playing time of 180 sec in the higher quality (22 kHz sample rate) and 360 sec in the lower quality (11 kHz).
  • ZIMO sound projects typically use high quality sound samples of 22 kHz.
  • 8 ohm speakers can be used with any ZIMO sound decoder which can be ordered from your ZIMO dealer. 
  • 4 ohms speakers or 8 ohm speaker arrays can be connected to the MX644 and MX645 models which have audio power up to 3 Watts.
  • Virtual cam sensor for sound synchronization of steam engines lacking a real cam sensor. A function output is programmed to send 2 or 4 signals per wheel revolution, which causes the sound module to playback a chuff sound with every signal received. This output is connected to the same input on the sound module that normally connects to a real cam sensor.
  • Most sound decoders have inputs for mechanical sound synchronization using cams, reed switches or hall-effect sensors.
  • Acceleration and load dependent sounds can be automatically adjusted by a test drive to set the load sensitivity parameters, and many other features (See the ZIMO Sound Database and User Manuals).
  • User Updatable - Install the latest sound files yourself, in minutes, without opening the locomotive.  All ZIMO sound decoders come with this feature (including function and accessory decoders).  ZIMO sound files are always available from the ZIMO or ZIMODCC web site. (Requires MX10, MXULFA, or other device)

 Two ZIMO "Sugar Cube" speakers with sound chamber (Part Numbers LS10X15 and LS8X12) produce high volume from a very small footprint.

 During selection of the speakers, bigger is always better.  It is very important to use a speaker enclosure, baffle or an airtight locomotive housing with a sounding board and openings in the housing, etc. for professional installation.

Click on the links below to download copies of the MX660 Connection Diagram and ZIMO Small Decoder Manual.


Operation Modes

  • NMRA DCC with 14, 28 or 128 speed steps
  • 2-digit (short) and 4-digit (long) addresses
  • Anaolg DC operation (de-selectable)
  • Automatic recognition of operational mode and DCC speed step selection
  • Supports Lenz LG100 braking sections, ABC brake sections and brake on DC


  • Runs DC and Coreless motors
  • 0.8A Continuous Load / 1.50A Peak Load
  • Silent, safe 40,000 kHz pulse width frequency motor BEMF
  • Motor output overload protected
  • Shunting speed and momentum key selectable


  • Audio Amplifier: 1.0W @ 8 ohms load
  • Speaker impedance: 8 ohms
  • Memory Capacity: 32 Mbit
  • 6 sound channels, all playable at once!
  • Library of over 40 US sounds available for download

Programming features

  • DCC Service mode & DCC POM (Program On Main)
  • Railcom feedback system
  • Railcom Plus Automatic registration

Function Outputs

  • 2 normal outputs
  • 4 common outputs
  • All Function Outputs Are Constant Current source for use with LEDs (Current 5mA; External Resistors Not Required)
  • Voltage Common (+) solder pad connection for each function output

* Additional Design Information provided in the Function Output Design Section below.

Additional Features

  • SUSI Compatible
  • 47uF Energy Storage Capacitor On-board
  • Direct Off-board energy storage capacitor support


  • 1.67 x 0.378 x 0.099 inch (42.3 x 9.6 x 2.5 mm) 


Top View of ZIMO MX660
Bottom View of ZIMO MX660
Top View of ZIMO MX660 on Atlas GP38-2 Chassis

(Note size of OEM Light Board Underneath and Width of MX660) 
ZIMO Resources

Here are links to a few of the key resources available for working with and using ZIMO DCC products...

ZIMO on Groups.IO

Application Notes

Programming The MX660

So this first question encountered is how to program a decoder like this.  

The simplest solution I have used for years with similar type decoders is to make a harness with test clips that plugs in easily to the MXTAPS or MXTAPV.

This harness was made using a TCS 1358 21MTC Adapter Board and SBS4DCC Test Clips.


MX660 Constant Current Function Outputs

The function outputs on the MX660 are designed specifically for driving LEDs directly. Regardless of the track voltage and the type of LED used, the function outputs provides constant current of 5mA. Dimming can be accomplished by programming the decoder's appropriate CVs.

Note however that since the functions outputs can only supply 5mA, they cannot be used directly to power devices requiring more than 5mA of current (like 12V Grain of Wheat incandescent light bulbs, smoke generators, or automatic uncoupling devices.

Here is the internal circuit which explain why there are no resistors at the outputs and why external resistor are not required.

The voltage at the 100R resistor is about 500mV so the current is about 5mA.  The power loss at the transistor for 22V rail voltage is: 22V - 2V (Led) = 20V * 0,005A = 100mW (Transistor allows 150mW) so a typical 3.2fV LED will not be damaged.

The current sources can be built for the same price as a simple output with a 1K ohm resistor.  The advantage is they always have the same brightness, independent of the rail voltage, and external resistors are not required when using LED's.  Also a capacitor will have a better effect, because the current source will compensate the falling voltage of the capacitor while it discharges.

If you want to connect more than one LED to an output, connect the LED's in series not parallel, so the current for every single LED will still be 5mA. 

The voltage of one white LED is about 3V so you can connect up to 3 LED's in series and it will still work with 12V rail voltage.

If you use analog operation, you can connect them in parallel (so they will work from 4V rail voltage) but they will be very dim and this only works with absolute identical LED's.  A white LED used in parallel with a red LED will definitely not work.

Installation Notes

N Scale InterMountain F3A

Fits easily in the well of an InterMountain F-unit.

N Scale Kato E8-A

Here is the Kato E-unit chassis...

N Scale Kato F40PH

Here is the Kato F40PH chassis...

N Scale Kato E8-A

Here is a Life-Like (pre-Walthers) E-unit chassis...

N Scale Atlas H15-44

Here is the Atlas H15-44 chassis...

N Scale Atlas GP38-2

Here is the Atlas GP38/40 chassis...

N Scale Fox Valley Models ES44AC

Here is the FVM GEVO chassis, although I would most likely use a MX649N for this one...

N Scale Life-Like GP20

Here is the Life-Like (Walthers Proto N) GP20 chassis...

N Scale Atlas RS3

Here is Atlas RS-3 chassis...

Looks like a pretty easy fit with room for a speaker in the cab!

N Scale Kato AC4400

Here is Kato AC4400 chassis...

Looks like a pretty easy fit with room for a speaker on the rear shelf.

N Scale Kato C30-7

Here is Kato C30-7 chassis...

Might a speaker in the cab so plan on cutting this frame for best fit.

N Scale Kato ES44AC

Here is Kato ES44AC "GEVO" chassis...

Looks like a pretty easy fit with room for a speaker on the rear shelf.

N Scale Kato GG1

Here is Kato GG1 chassis...

Decoder is a pretty easy fit but plan on cutting frame to make room for a speaker.

N Scale Kato SD40-2

Here is Kato SD40-2 chassis...

Looks like a pretty easy fit with room for a speaker on the rear shelf.

N Scale Kato SD70M

Here is Kato SD70M chassis...

You will probably have to cut frame to make room for decoder and a speaker on the rear shelf.

N Scale Kato Mikado

Here is the Kato Mikado chassis and tender...

Take your pick!


Just For Fun...
A big thanks to John Colombo for sharing this video of his installation in a Kato NW2.

Wow... Impressive work John!

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