Lionel FT sound performance?

Yes, the diode strings will do this, I have done it.  If this is conventional controlled, I have also tried wiring the motors in series, with good results.   

I have also added a thermistor with the diode string.   This is a device whose resistance decreases as it heats up, giving very slow and gradual acceleration from zero.

An older thread on using series wiring and a thermistor on a GP30.

Thanks!

I might give series wiring a try first since it’s no-cost and easily reversible...

Well, series wiring didn’t give me the desired effect... it did really tame the jackrabbit starts, but the maximum speed was drastically reduced, too much for a locomotive that could be called on to pull passenger trains.

The root problem of the locomotive starting to move as soon as the sound turns on, and the sound shutting off as soon as the locomotive stops moving, was almost unaffected...

What I’m looking for is the sound to start at something like 10 percent throttle (on the transformer) and the locomotive to start moving at something like 25 percent throttle.

The diode strings in series with the motor should solve the problem.  That reduces the voltage to the motor and keeps full voltage on the sound board.

It's unfortunate that Lionel saw fit to remove the battery connection from the Conventional RS-Lite board, a battery would have totally solved your sound issue at low voltages.

Should I expect a lower top speed with the diodes? (I assume the answer is yes)

If you're talking about the transformer at max, yes, you won't get the same speed as without the diodes.  OTOH, if you wire the motors back in parallel, I can't imagine it won't have enough speed.  If you need more speed than that, I'm out of ideas.

The drop in top speed (yes-max transformer) was drastic going from parallel to series, acceptable for a freight-only engine but too slow for passenger in my opinion... I’ve already gone back to parallel wiring...

Full throttle is too fast in parallel, but not fast enough in series. If parallel with diodes is somewhere in between that would work nicely!

Just ordered a bunch of diodes (1N4005). I’ll update when they get here and I get them installed...

You'll want to order again, that's not what you need.  Look for something like the 1N5400 3A diode.  1A is too wimpy for the job.  Search for them on eBay and specify US shipping only.

I thought I read in another thread that you used the 4005’s... thanks for clearing that up... don’t want to release the magic smoke...

1N5400’s ordered...

The smoke would come from the diodes in this case, but no sense in doing that.

Well, I put 5 diode pairs in series with the motors and it made no difference. The motors still start (loco starts moving) as soon as the sound starts. I guess it’s not supposed to let the engine run when the train isn’t moving to save fuel and lower emissions...

That's odd, you should have gotten at least 3 volts of drop through the diodes.

This is how I wired them...

I only showed 2 pair of diodes in the drawing because I ran out of space on the paper, but I had 3 more in line...

Not sure why that didn't work.

Is it possible that my MTH Z1000 comes in at a high enough voltage that there’s enough to spin the motors as soon as the engine sees voltage?

Edit: checked the voltage with the engine on the track, my fluke 115 true rms meter shows the voltage starting at 4.5v

I will say that it seemed to move slower when it started with the diodes than without, so I think they were doing something...

The chopped waveform does have a higher peak voltage right from the start.  Even when you crack the throttle, it'll be a fairly high spike.

Z-1000 as minimum throttle.

Here's the Z-1000 at half throttle.

And at full throttle.

Well that looks... interesting... I guess it works, but it sure doesn’t look good to me...