MRC 1908 Steam Sound Decoder

[electricity_bill]

Hello
A little bit help needed here.
I run DCC and I recently bought a PIKO mogul and fitted it with the PIKO decoder which works fine. I now want to add sound and thought that the PIKO offering was expensive at £115. I run lots of MRC decoder equipped locos but MRC no longer produce a steam power and sound decoder combined. However, they advised me that the 0001908 HO scale sound decoder would work on G scale DCC systems as it only requires a two wire connection to the pickups. I got one for a fraction of the PIKO price but there is a snag. The MRC installation section of the manual says ”If the track voltage exceeds 16V, a special voltage reducer is required to be used in line with the sound decoder”. Contact with MRC revealed that they do not make such a device but Doug at MRC was talking about making one using two diodes connected in parallel in opposite directions to create a volt dropping unit of say 1.5V on AC. You then connect four of these together in series to drop my Massoth Navigator output voltage from 22V to 16V. Anyone any experience with this arrangement?
Bill

 

[PhilP]

It is used quite a bit to reduce track voltage for certain items, whilst still allowing the DCC signal information to get through..
Just make sure you use 'fast' diodes, so as not to degrade the signal too much. - I would guess 1Amp diodes would be plenty for a small sound decoder.

My only worry would be whether a HO/OO unit would have the 'oomph' to produce enough volume??

 

[Neil Robinson]

It is used quite a bit to reduce track voltage for certain items, whilst still allowing the DCC signal information to get through..
Just make sure you use 'fast' diodes, so as not to degrade the signal too much. - I would guess 1Amp diodes would be plenty for a small sound decoder.

My only worry would be whether a HO/OO unit would have the 'oomph' to produce enough volume??

Interesting; I naively assume that "fast" diodes are more modern in design and have a reduced forward voltage drop compared to standard ones. If so one or two more inverse parallel diode pairs than anticipated may be required to give the required 6V drop.

 

[PhilP]

Another thought..
Are you MTS or Massoth?

Not sure on the MTS unit, but the Massoth central station has a facility to set the track voltage I believe.

 

[electricity_bill]

As I said in the post, I use the Massoth system and I can set the track voltage which I thought should be about 22V for large American outline locos.
Bill

 

[PhilP]

The top voltage you will need depends a lot on whether you intend to run at prototypical scale speeds.. Most models will go off like a scalded cat, and you may well find you do not need to run to anything like the full voltage you have available.

 

[Railway42]

A diode only drops the voltage by .7 of a volt i.e. 1N400* a fast Schottky diode only drops the voltage by .4 of a volt. So if you must use a decoder that is not meant for the larger scale you will be better using a central station like the Massoth that you can set the track voltage on. Remember DCC is bipolar so your DVM will not be any good for measuring it.

 

[beavercreek]

Hi bill
I run US locos (many big jobbies)and I always set the voltage at 17 or 19 volts on my Massoth. In fact the Bachmann three truck shay with factory DCC, and also the new DCC endowed climax, prefer 18v.
All Aristo and USAT and even LGB big US locos will work perfectly fine with 17v max. In fact they will look more prototypical run at lower speeds, and also take longer to go around the layout.

 

[Gizzy]

I have a couple of the diesel sound decoders fitted to LGB locos (a V51 and a V14).

They were around £60-70 and I found them in my local model shop. I remember they also had G scale steam sound decoders in stock.

You could contact them on 01284 753456 and ask for Keith or Dave, or visit http://model-junction.co.uk/....

 

[stockers]

or use a voltage regulator - £3

http://pendleburymodels.com/wp/shop/voltage-regulator-adjustable-step-down-supply-power-module-1-5-35v/

 

[PhilP]

or use a voltage regulator - £3

http://pendleburymodels.com/wp/shop/voltage-regulator-adjustable-step-down-supply-power-module-1-5-35v/

Err... How does the DCC signal get through a regulator?

 

[stockers]

Fair point. :-[