Filtered A.C. ???

It's possible, but very expensive.  You can take almost any type of waveform and with sufficient filtering, it'll be a pure sine wave.  However, for high power waveforms, the filters will be big and expensive.

A much cheaper solution is to buy a pure sine wave transformer,  the Z-4000, MRC Pure Power, or any of the many post-war models like the ZW, KW, or similar come to mind.

Thanks John. I was sure something like that would be the answer. It's funny in conventional mode, (no tiu) all engines with electronics, including ps1 and ps3 work perfectly. With it run thru tiu the ps1 and ps3 work perfectly, even in command mode, but the lionel do stupid stuff, horn or bell sounding more than they are off. I've got a z750 brick and a couple of 1033's. This is just like personal computers, you change one thing and it's not compatible with that. But then this is the same thing, just different peripheral and input devices............ If memory serves, (and it doesn't very well),  I believe I read in the ProtoSound doc's that they first used a 286 processor. I know the first solid state Whirlpool washer used the 8088 processor that was in the IBM PC.

The chopped waveform is pretty well filtered in modern engines, but the older stuff was designed in the era of pure sine wave transformers.  That's probably why when MTH did the Z4000 they went the extra mile to generate true sine wave output.  I've had PS/1 stuff that won't run properly on the variable channels of my TIU, I have to break out a pure sine wave transformer for testing.  I have also seen the horn or bell go off randomly on Lionel conventional stuff with the same setup.

Yeah I guess it's the combination of the MRC and the TUI, too much for the Lionel Engines. Both work good with either the MRC alone or thru the Vari Channel with a Z750 brick supplying the power.

Dio, I suspect the problem is double chopping.

The Z bricks have Pure Sine wave out that gets chopped in the TIU for variable channels.

IF the MRC uses Chopping to reduce power, then it goes thru the TIU and gets chopped again you will have a very nasty waveform.

I can state that the Z controllers also chop the wave, but if you want to run them thru the TIU just turn them up to full power, they are not chopping at that point.

You might try the same thing with the MRC.

There is a way to clean up the chopped wave a bit. The trick is finding the right parts. What you want is NON-POLARIZED electrolytic capacitors. Start with 100uF and add them in 100uF increments (parallel). Make sure they're non-polarized as regular electrolytics will burst (possibly violently). We used this with the Lionel TMCC Powermaster TMCC-controlled throttles. It worked for a lot of QSI-equipped conventional engines.

You know funny enough, I have a number of 94 and 100uF non polar caps. Voltage considerably higher than would be needed. I save them from micro waves.

How would I hook up the caps?

Directly across the output voltage from the controller creating the chopped waveforms.