DCC & PFM Sound System - Are they compatible?

[Anonymous]

I recently purchased an old (1971) PFM sound system (Mark II?) that came with a Locomotive/Tender Module (LTM) and a reverb add-on system. I also have an MRC Command 2000 DCC system and several decoders, as well as a PFM Tenshodo Big Boy that says it's "PFM Sound Ready". What I'm wondering is if the PFM Sound System is compatible with (i.e. won't cause interference to) the DCC system?

Installing the LTM is a fairly complicated process from what I've read and requires removal of the tender body from the frame (no big deal -- looks like 4 - 6 little screws). It also requires rewiring the power to or from the loco motor through various capacitors or diodes and the LTM module. I was thinking that while I'm going to all this trouble to install the sound module, perhaps I should also install a DCC receiver at the same time.

Any thoughts or advice on this project would be much appreciated. Also, if anyone can tell me what the purpose of the reverb system is and if it is worthwhile adding, that would be a big help.

Thanks,
Bill V.

[cacole]

Personally, I doubt very much that the PFM sound system will work with any DCC. DCC was not invented yet in 1971, so the PFM has to use something different. I wouldn't risk putting that PFM engine on a track with DCC power on, because the DCC voltage is likely to turn it into a smoke generator.

[DanRaitz]

NO

[ndbprr]

As the owner of a PFM system it is what has prevented me from going DCC . here is how it works. First of all there is a small AC current on the rails. a capacitor is placed so one side is always hot and loads the capacitor with AC. A driver is painted with something like nail polish and then four sections are removed so when the capacitor completes the circuit you get the chuff sound. This is then sent back to the main unit where cut off and tone are adjusted. It is added to all the sounds like whistle and bell and the tape sounds and sent to the moduile in the tender as a radio wave. the module cuts out all the extraneous background noise like the capacitor firing and plays the sound through the speaker usually located in the tender. The control of the motor is straight forward dc or pulse depending on your preference. It could be possible to figure a way to control the lights and motor from a DCC module but you will be doing a lot of experimentation and breaking new ground. Those of us with several engines with this system would be extremely gratefull if you succeed and let us know how you did it. My PFM system was about $700 twenty years ago and I have loved it. The actual cost per engine was about $15.00 at most. Something those selling sound decoders should take into account. there is no reason for the pricing of sound equipped decoders that I can see.

[rrinker]

Sure there is - the PFM LTM is little more than a DC block to keep the DC track power from frying the speaker, yet allowing the audio waveform to pass through. it SHOULDN'T cost more than $15. It's about $5 of passive electronic components, if that.
A DCC sound decoder is completely self contained - the sound samples, , audio amplifier, motor drive, lighting control, etc. is all built in to the decoder, using modern highly integrated surface mount electronic components. The advantage of having the actual sound generation components external menas they can be as big as they want, there's no size restriction to make it fit into an HO (and even N scale now!) loco body. Big components are still cheaper, when you miniaturize, the cost goes up.
I'm not knocking the PFM system, it's really awesome. It was INCREDIBLE in 1971, still amazing in 1980, although starting to get a little behind - I mean, the reverb unit is a MECHANICAL delay line, not solid-state. Also keep in mind that the 700 1970's dollars you paid for that, translated into today's dollars, would buy you a DCC control system and a lot of those 'expensive' sound decoders. And allow you to do something the PFM system NEVER could - run multiple locomotives with sound at the same time under completely indpenedent control - and independent sounds.

--Randy

[Anonymous]

Many thanks to all of you who responded to my dilemma, especially ndbprr and rrinker for the detailed explanations. I can see the advantage of having the sound generator in the locomotive or tender -- conceivably, each engine could then have its own unique sound signature, just like the prototypes. So DCC sound is probably the wave of the future.

On the other hand, if both DCC control systems and PFM sound system expect AC voltage on the rails and convert it to DC or pulse power for motor and lighting control, it seems like they would not necessarily interfere with each other. The LTM has outputs to provide constant lighting, just like DCC. I guess the big problem would be if the DCC and PFM systems both used the same RF band. Does anybody know what frequencies the PFM system uses? How about DCC?

The only consideration I found in the PFM system for multiple unit consists was the ability to set different whistle sounds for up to 5 locomotives. Otherwise, I guess since the sound is generated in the "Sound Generating Unit" (which is also a transistorized pulse throttle), all engines would have to sound pretty much alike, the only difference being supplied by the ability to alter the spacing and width of the exposed contact surfaces on the driver that has been painted with non-conductive paint. Of course, one of the nice things about the PFM system is that the control unit has potentiometers or rheostats on just about every sound control, so you can alter the engine sounds on the fly to satisfy your own preferences.

Please don't interpret anything I say as any evidence of my expertise on this subject: I'm a retired software engineer. I've worked with enough "sparkies" (hardware engineers) to gain a basic knowledge of electronic principles and can even sort of read a wiring diagram. My whole knowledge of DCC and PFM sound systems has been gained in the past week by reading the PFM manuals and the book "DCC Made Easy" by Lionel Strang. In short, I'm still more comfortable with DC circuits and the old pulse power throttles.

Thank goodness I didn't spend $700 on this PFM system -- I picked it up (new, still in original boxes) in an ebay auction for $88.50 plus shipping. So it's not the end of the world if I can't make PFM and DCC play together. Still, I kind of like the challenge of making them work together, so I may just give it try.

Bill V.
Central Arizona

It also seems to me that both DCC and PFM sound system will be susceptible to signal loss through long track runs without additonal boosters or poor trackwork.

[ndbprr]

You have the basic unit with limited functions. I have the other one that addresses all the issues you mention. It has five switches for the whistle that have a low and high position plus a range knob that allows five different bands for each switch. there is also a "Hiss" knob that lets you adjust the volume of steam in the whistle sound. The cylinder steam noise can have the cut off and tone regulated. In addition there is a tape deck with three four track endless loops tapes that have three or four bells, air compressors, wheel noise, coupling noise, generator, blower and maybe a couple of more. I hate to give it up.

[rrinker]

If you install blocks like a standard DC system and connect one cab tot he DCC and one to the PFM, you can run. You just have to be careful about crossing the boundaries. I don't think the PFM system will work superimposed over DCC, the DCC signal is a variable square wave, not a nice neat AC sine wave. I would expect at a minimum, interference in the sounds. Worst case it will damage the PFM console and/or your DCC booster.

ndbprr, you don't 'give up' anything by going to loco-mounted DCC sound. The 'good' sound decoders (ie, NOT the MRC ones) use actual digitized sounds from prototype locomotives. No pre-recorded whistle blasts, YOU pick how long to sound the whistle. The newer ones coming out even have multiple sounds on the same decoder so you can select it yourself, rather than buying a specific one, and also now there is the capability to upload your own sounds into the decoder. About the only thing missing is the true analog control of the whistle, and even that's on the way.

--Randy

[Anonymous]

ndbprr: Yes, your PFM system is definitely more advanced than mine -- there's no tape deck on mine and only 1 whistle switch, though it does have the hiss control and 5 range whistle tone control. The more I think about it, the less appealing it sounds to try to install the LTM in the Big Boy. Now I'm thinking of perhaps just using the LTM as an external speaker mounted under the layout. Was I right in that the PFM sound system only controls one locomotive at a time? That is, there is no provision to send different sound signals to a multiple locomotive consist?

The manual says that if I want to use an external 8-ohm speaker, I need to insert a PFM-03 "RF Trap" and a PFM-05 "Audio Bypass" into the line going to the speaker. Anybody know what those components actually are? Are they something I can maybe find a substitute for at Radio Shack?

But if I use the LTM as the speaker, wouldn't that already have the necessary electronics for the RF Trap and Audio Bypass? I could even wire up an old DC motor to the LTM with a wheel attached to simulate the driver with the non-conductive paint for the wiper that feeds power to the capacitor. Since none of the PFM sound system would actually be connected to the track bus, it should have no effect on the DCC that uses the track bus, right? Or is the absence of the track load likely to cause problems with the PFM Sound Generator?

rrinker: Who's sound decoder would you recommend? You mentioned not liking MRC. How about Digitrax? I've also heard of an outfit called "Soundtraxx", but don't know if they make sound decoders for steam engines. Also, is the sound decoder a separate item from the DCC decoder or are they combined?

Guess I'm still confused. ;-)

Thanks again for any input.

Bill V.

[rrinker]

Digitrax doesn't make any sound decoders, just motor decoders. Soundtraxx has steam and diesel both. They also have some that are sound only (so you'd use another decoder for the motor, like a Digitrax or NCE or TCS), and some do the sound AND motor control.
Soundtraxx decoders might be tough to come by, everyone is waiting on their new Tsunami line, which will have higher quality sounds, work on DC and DCC, and will be both sound and motor decoders.
The other major US maker of sound decoders is QSI, but they (so far) do not sell seperately, just OEM to companies like Broadway Limited, Atlas, and Life-Like. Sound locos from these companies all have the QSI sound/motor decoders.

--Randy

[SP4449]

[:D] This is great! I feel like I just walked up to some guys at a train show. What a post! [^]

[rrinker]

That's nothing, I spent about an hour in the LHS yesterday helping out a guy who just got into DCC. He was adding to his layout and was creating a few reverse loops and wanted to know what to do with DCC. I wonder if you get a discount for workign there, could take a part time job there to fund my layout construction, the downside being, I wouldn;t have any time left to actually build the layout with a second job.

--Randy

[Anonymous]

Randy, Thanks for the excellent info on sound decoders. I know what you mean by how much time you can spend helping "newbies" like me. I've done the same thing trying to help others with computer issues. The only payment is in the satisfaction of helping someone else with their problem.

OK. I finally dug out the manuals, etc. for my 8 year old MRC Command 2000 DCC system. Yep, it is pretty limited, but probably adequate for my little Christmas layout that I'm building. I think I can use it for the Christmas layout as I don't expect to have more than a few trains running at the same time on the limited amount of track that layout will have. Most of the engines on my Christmas layout will be smaller 4-4-0's, moguls and ten-wheelers, so the MRC decoders should fit OK with a little work. Also the layout has no reversing loops, so I should be able to stay of trouble in that regard.

As for the PFM sound system, I can either use it stand alone on the Christmas layout like I described previously (except I figured out I'll need to use the whole motor and driveline with drivers from an old engine, or the "chuffing" would be way too fast.) or I can sell it with the PFM Big Boy as a package deal. Since the PFM sound system is no longer state of the art, I suspect using it as a stand-alone sound generator on the Christmas layout is my best option. When I finally get a space to build the "big layout", I'll look into more capable DCC-based sound equipment.

Thanks again for everyone's input on this.

Bill V.