Farish Class 37 with Zimo MX660 drop-in sound decoder - install

[John YouChoos]

A little-known product released recently by Zimo is their drop-in DCC Sound decoder for N gauge - the MX660. Basically a very thin single-sided PCB with solder connection pads around the edge.

It is designed for Kato models, but works just as well in Farish N gauge (and probably some Dapol models too).

 

The MX660 is a full sound decoder, with 6 lighting outputs, similar spec to the MX648.  Solder pads are very well laid out to be in good positions for direct connection to pickups, motor and lighting.  On top of this, all 6 lighting outputs are 3V rather than the usual 12V, which means you can directly connect them to LEDs without needing a resistor - brilliant idea!

 

 

Here are some photos of it being used in a Farish Class 37 diesel to great effect... this means DCC sound, decent speaker (YouChoos SugarCurve6) with absolutely no modification to chassis or plastic.

Full install guide here:

http://youchoos.co.uk/Index-Resource.php?L1=Guides&Item=N37MX660

 

Here's the MX660 with some of the wires attached with standard DCC colours:

Pickups connected, re-using the screw rings from the original factory PCB of the CL37:

Motor wires soldered directly to motor terminals, and SugarCurve6 speaker just sits onto of the chassis (protected from shorts of course):

Lighting connector boards joined in:

All back together:

We configured ours for independent control of front and rear lights, so 4 of the 6 AUX lighting functions of the MX660 are used doing this.

 

You could stop there, and you'd have a very easy DCC sound Farish Class 37, with a good level of sound from that speaker... but, we decided to add in SACC16 with a 330uF Tantalums to give more reliable running too:

The extra backup power from the single Tantalum is not really visible in terms of run-on time, but you really notice the difference when crawling at slow speed - hardly ever cuts out.

 

We also added independent cab lights and crew, but, that's beyond this topic!

 

Enjoy

 

[North Star]

Brilliant addition of the 3V supply to save the need for lighting resistors!

[woodenhead]

Wow, did not know about this product - so if I get brave I could fit sound to my 37s and 47s.

 

Wonder if this would work with a class 25 and if my Dapol 26/27s ever decide to burn out their PCBS then this would be a nice replacement.

[North Star]

I’ve found the issue tends to be the speaker size so as not to have to perform ‘surgery’ to the chassis. YouChoos do a really good range of different speakers. The 6mm sugar curve from my experience gives a good sound level although there are even smaller ones that work pretty well.

For an N Gauge 25 the length of the chip and speaker might be a bit tight but I have successfully used the Zimo 648 chips in these Farish locos even with space for the resistors for the LEDs.

I am certainly going to experiment with these new chips as it looks like they will save the extra hassle of gaming to do a resistor ‘array’ for the lights. The 6 outputs also will allow for independent directional and cab lighrs