# LGB ALCO 2056 Rio Grande using factory sound board with DCC



## beavercreek (Dec 12, 2008)

I have an old LGB ALCO diesel 2056 'Queen Mary Edition'

It has had LGB DCC decoder fitted later but is mute as there was no sound board fitted.
I have picked up a factory sound board, the long one piece one with the back-up capacitors on board for a very cheap price (about equivalent of 10 dollars).
I tested the board on its own with DC and DCC power.

With analogue DC it did not make a sound until I just plugged in a sensor into the horn/bell socket on the board and placed the sensor next to a nearby magnet . Then it worked fine and 'knotched' up and down with the DC controller and had the standing shutting down sound fed from the caps.

With DCC it burst into sound with an initial horn blast, then into the diesel 'idle' sound. It did not respond to the DCC handset to 'knotch' up or down, it just kept on idling (the loco address of the DCC controller was on 'analogue). When power was shut off, the caps fed the shutting down sounds the same as with DC.

Now this sound board is the same age as the loco and has two banks of three pin connection from the motor blocks (white, brown and green). So it preceeds the real mass use of DCC in LGB locos. As I had got it for peanuts, I would like to try to use it somehow with the DCC decoder in the loco.

I could replace the lot with a single sound decoder but I do not want to yet, invest more money when I can possibly get what I have to work.

Is the sound card just too old to 'understand' when the the DCC PWM wave is increasing the voltage? I have used LGB Sumpter/Uintah mallet analogue sound boards in Annie tenders with hall sensors and they work a treat on both DC and DCC but they probably are newer in design that the ALCO soundboard and deal with DCC better.

I had thought of maybe using a rigged up circuit that would convert the PWM from the DCC supply (track or decoder) into pure DC and therefore the board would react as if it was on an analogue DC supply...does anyone know of something like this?


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## Greg Elmassian (Jan 3, 2008)

I think the sensor is intended to be next to a wheel that is turning, to give it a "speed" signal. 

There's a couple of experts here that I am sure will know exactly what the board "wants" and how to most easily get it going. 

The Train-Li people (Axel, Dan), Mohammed (Massoth evangelist), and Keith .... 

Greg


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## TheRoundHouseRnR (Jul 15, 2012)

I have two of these boards. They do not use hall effect sensors for detecting speed. They take info from the track voltage to adjust idle .This is why using DCC confuses the board. What doesn't make sense to me is why you plugged in reed switches to get it working on the bell and horn input. Mine will fire up with nothing more then power to the board and a speaker. Strange... Are you sure you ramped up the voltage enough to get it to power up the first time you tryed? 

The Roundhouse RnR


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## Greg Elmassian (Jan 3, 2008)

So they are DC only? Makes sense... must be a FW bridge on the input so it's getting full track voltage, never going through the startup cycle? 

Greg


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## beavercreek (Dec 12, 2008)

I had 'ramped up' the DC voltage to full whack and the soundboard, as I said in the first post, would only initially start when a sensor was connected and then it behaved perfectly.

I have investigated further and indeed it does not use a hall sensor but uses a bespoke sensor plate (not the usual add-on type as used in the LGB Mogul loco), on the bottom of the block, for detecting the track magnets to trigger the horn or bell.

Under DCC 
I have looked at the age of the Alco soundboard and compared it to the age of the Sumpter/Uintah mallet analogue soundboards that I have working perfectly fine when powered by DCC, and it is definitely from the era of the older 'three wire' motor blocks. The motor blocks obviously can be DCC-ed by altering the 'fourth' wire path but the soundboard is just not rigged for accepting the PWM signal/carrier used in DCC. unlike the Sumpter/Uintah mallet ones.

That is why I asked if anyone has had any success with a circuit to change a DCC PWM signal into pure DC. 
This circuit would probably be like the Aristocraft CRE _57090_ TRAIN ENG. PWC TO LINEAR board that facilitated using the old Soundtraxx Sierra analogue soundboards with the Aristo Revolution receiver boards which also put out PWM (PWC in Aristo-speak)


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## Greg Elmassian (Jan 3, 2008)

Ahh... "bespoke", you will need to translate that from England to American English please... I believe the right translation of "bespoke" is "custom made". 

It must be a reed switch if it's not a hall effect sensor (which normally take 3 wires)... 

Yes, your determination that it works with the 3 wire motor blocks guarantees that since the locomotive could NOT be DCC, it stands to reason the sound unit is not either. 

DCC is a constant voltage square wave of varying frequency... Using a full wave bridge rectifier only gives you a constant DC voltage. Not of much use in this application if the "speed" is sensed by the DC level on the track... your DC level would always indicate 150 or so miles per hour ha ha! 

Greg


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## beavercreek (Dec 12, 2008)

Hi Greg
The reed sensor used in the Alco is like a flat plate with a prong that inserts into the motor block onto which the lead plug from the soundboard is connected.
Yes 150 miles per hour might not be the best but..
Given that the Aristo CRE 57090 board does exactly for the PWM output from the Revo board, what I would like to do for DCC to drive the Alco sound board maybe I should try one of those...I have three of them to put into battery locos where a Soundtraxx sierra card already exists.
The 57090 takes the PWM wave frequency and apparently turns it into a DC voltage level. This is all that the Sierra needs to give the correct speed sound register.


I expect that this little investigation might end up with a non-realised implementation but it will be good for my learning bank to have gone through the process.


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## Greg Elmassian (Jan 3, 2008)

No, you misunderstand the difference between PWM and DCC. 

PWM is a unipolar pulse with varying pulse width... ZERO volts between pulses. 

The longer the pulse, the longer power is "on" to the motor... it "averages" the on and off times. Faster is longer pulses. 

DCC is COMPLETELY different. 

First it is a bipolar square wave... the positive cycle is EXACTLY mirrored by a negative cycle of the same duration (frequency)... so when you rectify it with a full wave bridge you get twice the duration at full voltage.. ALWAYS full voltage, since the square wave is ALWAYS symmetrical.... you will get a constant DC, because the individual cycles / frequencies, besides being symmetrical, has NOTHING to do with the speed. 

The durations of each cycle is related to a digital coding of data so that commands can be sent... 

Even if you only used a single diode, so you got pulses of voltage and then zero volts, there is no relationship between the average voltage and the speed of ANY loco, not just the loco you are interested in. 

Try hooking the sound unit to the motor... and possible some filtering... that is the only place you have even close to variable DC in your setup. 

Regards, Greg


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## beavercreek (Dec 12, 2008)

Ahhhhh now I get the difference between PWC (PWM) and DCC wave forms. Excellent, many thanks Greg!


When you say to use the feed from the DCC decoder to the motor as the supply for the board as being 'as close to DC as I will get'. Does this mean that the decoder gives out PWM which could be then be either converted by a circuit with a choke like the Aristo 57090 or the bigger 57091 (http://www.trainelectronics.com/ART5700TrainEngineerRevolution/PWC--Linear_CRE57091/index.htm) and fed to the soundboard *o*r just be fed directly to the soundcard


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## Greg Elmassian (Jan 3, 2008)

Yes, the motor itself will smooth out the pulses somewhat, then you could take that output, put it through a filter/choke and you should be in good shape. 

A filter like the Remote Control Systems BIK-TC5 would be a good choice...


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## beavercreek (Dec 12, 2008)

I appreciate your wisdom on this Greg.
I will try the board out with the filter/choke...fingers crossed.

On a totally different matter do you know where I could get any of the older version QSI quantum boards?

Mike


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## Greg Elmassian (Jan 3, 2008)

There's also a filter from Aristo, though it is not as "thorough" as the RC Systems one, only a single choke. 

No I don't know of any older QSI's available, I'm upgrading to all the newer ones, and as soon as I announced that, I had a waiting list that spoke for all of mine. 

People will come across them occasionally, like Stan C. and Rex A. 

Regards, Greg


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## Mike Toney (Feb 25, 2009)

I had a yellow/green LGB Alco that had both MTS and sound on board and it ran great on my NCE system. Mike


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