DCC Sound and Control for a K27

[joeaug1025]

What manufacturer(s) make a DCC decoder with sound for the Bachmann "F" scale (1:20.3) K27 that plugs directly into the PC board connector

[jviss]

http://www.bachmanntrains.com/home-usa/board/index.php/topic,23261.0.html

[StanAmes]

What manufacturer(s) make a DCC decoder with sound for the Bachmann "F" scale (1:20.3) K27 that plugs directly into the PC board connector

Unfortunately here are no current DCC decoders in the market that plug directly into the K27 and work for all functions out of the box.

QSI and Zimo both make excellent sound decoders with plugs that plug into the socket and work perfectly with all the socket equipped Bachmann Spectrum  locomotives except the K27

The problem is the chuff.  The K27 has a positive trigger and the decoders desire a ground trigger.  It is easy to insert a transistor to invert the chuff. See the documentation that Bachmann has on its site for instructions.

Another good alternative is the ESU large scale decoder. This decoder works with both a ground or a positive chuff and is an excellent decoder.  To install it in a K27 you use wires from the dummy socket to the decoder.  Bachmann makes a dummy board with wires that you simply screw into the decoder and includes this part with all other Spectrum locomotives.  I have not seen it offered as a separate part but perhaps if you call and ask they can find one for you.

Hope that helps

Stan

[jviss]

What manufacturer(s) make a DCC decoder with sound for the Bachmann "F" scale (1:20.3) K27 that plugs directly into the PC board connector

The problem is the chuff.  The K27 has a positive trigger and the decoders desire a ground trigger.  It is easy to insert a transistor to invert the chuff. See the documentation that Bachmann has on its site for instructions.

Hi Stan.  I'm brand new to DCC, and the only decoder I have is the Soundtraxx Tsunami TSU-1000, and my reading of the docs was that it wanted a trigger from the rail.  That's because the installation manual explains how to wire a trigger wire that is insulated from the frame and connected to the chuff input, , and contacts a "cam" disc that is adhered to a driver wheel, the conductive sectors of which are electrically connected to the driver, and thence the rail.

Perhaps even more to the point, there is no ground reference exposed from the Tsunami decoder!  The "function common" appears to be a Vcc reference, the function outputs apparently open-collector outputs.  Other than speaker outputs there's rail in and motor out; no ground reference.  To have a ground reference you'd have to make a guess as to how Soundtraxx established this inside the decoder, and then synthesize this with a circuit outside, perhaps a FWB rectifier and assume the more negative of the rectified output of is "ground."  

What I am saying in a roundabout way is that in DCC, because the rail voltage is alternating, there is no "ground."

Do I have this wrong?

Thanks,

jv


UPDATE: I just today wrote to Soundtraxx support, and they responded, and have confirmed what I surmised about the chuff input: it's "looking for rail power."

[Hunt]

An aside -

SoundTraxx Tsunami Exhaust Control

Also, be aware that if you select cam-synchronized exhaust, the Tsunami will
automatically revert to auto exhaust when operating in analog (DC) mode.
This is because the cam sensor circuit requires an alternating voltage polarity
such as found on a DCC track in order to work properly.

[StanAmes]

Hi Stan.  I'm brand new to DCC, and the only decoder I have is the Soundtraxx Tsunami TSU-1000, and my reading of the docs was that it wanted a trigger from the rail.  That's because the installation manual explains how to wire a trigger wire that is insulated from the frame and connected to the chuff input, , and contacts a "cam" disc that is adhered to a driver wheel, the conductive sectors of which are electrically connected to the driver, and thence the rail.

Perhaps even more to the point, there is no ground reference exposed from the Tsunami decoder!  The "function common" appears to be a Vcc reference, the function outputs apparently open-collector outputs.  Other than speaker outputs there's rail in and motor out; no ground reference.  To have a ground reference you'd have to make a guess as to how Soundtraxx established this inside the decoder, and then synthesize this with a circuit outside, perhaps a FWB rectifier and assume the more negative of the rectified output of is "ground."  

What I am saying in a roundabout way is that in DCC, because the rail voltage is alternating, there is no "ground."

Do I have this wrong?

Thanks,

jv


UPDATE: I just today wrote to Soundtraxx support, and they responded, and have confirmed what I surmised about the chuff input: it's "looking for rail power."

JV

The Tsunami TSU-1000 is not an appropriate decoder for the K27 for many reasons

1) insufficient current for the K27
2) DCC track voltage in Large Scale is higher then the Tsunami TSU-1000 support
3) The K27 needs both a decoder + and decoder - connection to operate properly.  Most Large Scale decoders support both.  Many decoders designed for smaller scales do not.

Soundtraxx announced a decoder for the Large Scale socket found in the Bachmann Spectrum locomotives but to date has not released the product.

BTW another good alternative is a non sound decoder and a sound only card. The SJR&P uses Lenz Gold Maxi decoders with Phoenix sound`

[jviss]

JV

The Tsunami TSU-1000 is not an appropriate decoder for the K27 for many reasons

1) insufficient current for the K27
2) DCC track voltage in Large Scale is higher then the Tsunami TSU-1000 support
3) The K27 needs both a decoder + and decoder - connection to operate properly.  Most Large Scale decoders support both.  Many decoders designed for smaller scales do not.

Soundtraxx announced a decoder for the Large Scale socket found in the Bachmann Spectrum locomotives but to date has not released the product.

BTW another good alternative is a non sound decoder and a sound only card. The SJR&P uses Lenz Gold Maxi decoders with Phoenix sound`

Thanks for your reply, Stan.  I mentioned the Tsunami not as a candidate for the K27, but as an example of exhaust chuff triggering that is not referenced to ground; I was reacting to your comment "The K27 has a positive trigger and the decoders desire a ground trigger."  I don't know how other encoders are triggered, but I can say for sure that this one doesn't 'desire a ground trigger.' 

Regarding the track voltage, the Tsunami does indeed comport with the NMRA track voltage standard, i.e., maximum operating voltage of +/- 22V, absolute maximum voltage of 27V.  This is in NMRA s-9.1_electrical_standards_2006, and the Soundtraxx Tsunami documentation.  I would point out a flaw, or imprecision in the NMRA standard in that it cites the absolute maximum voltage by saying that the decoder "shall be designed to withstand a DC voltage of at least 27 volts," without mentioning an upper bound; it should state, in my opinion, the maximum voltage one will see on the track, and that would be stated as a maximum, not "at least."  But I digress.  The Tsunami complies.

On the third point, I don't understand that: what is "decoder +" and "decoder -"?  Is this the same as the pins 6 and 7, "decoder positive" and "decoder ground" in the document you sent me?  (Topic 0707092 Large Scale Plug-socket.pdf) 

Thanks,

jv

[StanAmes]

jv

Sorry for the confusion.  I was trying to answer the questions in context for use with the K27

SoundTraxx makes excellent products just not currently a retail product suitable for track powered DCC Large Scale applications from both a voltage and amperage standpoint.  They used to produce a product called Sierra that was designed for Large Scale use and they announced a excellent plug in decoder for Large Scale that has yet to be released.

I do not have a new production Tsunami TSU-1000, to double confirm with. Past product that I have will shut of the motor and sound at about 20-21 volts DCC. Fine for the smaller scales but a little low for Large Scale.  My track voltage is around 21.5 volts DCC.  It is not uncommon to see Large Scale DCC track voltages at 24V DCC even though this is above the standard.

SoundTraxx and Bachmann teamed up to produce a plug in a sound decoder for the Climax which does work at the higher LS DCC track voltages and has a suitable amperage for the Climax.  This board will also plug into a Forney but does not have a suitable amperage for the K27, the 2-6-6-2 or the C-19

Hope that answers your questions.

Stan

PS  Decoder+ is Decoder Positive and Decoder - is Decoder Ground.

[jviss]

Thanks Stan.  So, you think 22 V max. operating voltage is too low for large scale?  I wouldn't know from experience, but I can imagine with grades exceeding scale grades, long trains, and tight radii curves one might want more voltage for a BBH.

I'm curious, at what point are you controlling the voltage, i.e., where are you measuring 21.5 V?  If it's at the track how are you measuring it?

Thanks,

jv

UPDATE: I got curious about this, and made some measurements on my new famous maker booster.  I can take the input up high, to like 25V DC, but once a certain point is reached the track voltage doesn't increase, so the track voltage is regulated.  This can be adjusted, and also the DC offset can be adjusted.  From the factory mine is a track voltage of 19.86V, with an offset of 0.04V.  I measured using the prescribed digital multimeter differential method.  I'm going to fire up the 'scope and take a look later today.