It's worth explaining that a SC-50 is in fact a SC-55mkII minus MT-32 tones. And that's what this unit is, a SC-50 with sequencer - well, probably!
I don't believe the service notes/manual are available for this device, so it's hard to be sure that it uses the UPD63200 DAC, and so on. It could be a hybrid SC-50 with some (lesser) 55 parts. If you want to confirm which UPD DAC is used, that would be VERY helpful and appreciated!
But, *most likely*, it's what I said in the first line, and what you implied.

The MT-200, from reading the manual's specs, is based on the SC-55. Lower polyphony and less GS instruments, but has the MT-32 bank.
You're right though, misinformation abounds about Sound Canvases, which is why I (somewhat naively) tried to make a project about cataloguing them. Google first page of results for the MT-200 had some confusing the specs with the 120, some with the SC-55mkII..

Just had a look and it uses the UPD6736 DAC which itself appears to be the 16-bit only baby brother of the UPD63200. It's pin-compatible, with the only difference being that pin 3 that selects between 16/18-bit on the UPD63200 is not connected on the UPD6736. I imagine you could 'upgrade' it if desired, but to be absolutely honest I've struggled to hear any difference between my MT-120 and my SC-55ST, and looking at the spec sheets between the two chips shows very little difference in performance characteristics.

Here's a list of the rest of the chips if interested:

Hitachi HD 63266F
Roland R15239186
NEC D70325GJ-8
Roland R15239187
Hitachi 65256BLFP-12T
SRM2A256SLM10
Roland LCGS-2A R15209486
Roland R15199827
Roland R15239229
Roland R15279824

The format which Roland and many japanese things in general outputs is Left Justified which, unlike I2S and Right Justified (LSB aligned), requires receiving side to explicitly know how many bits is transferred or you get messed up output since bits are actually misaligned and all zero crossings get lost because the sign bit gets misinterpreted which results in not so nice things 🤣.

I2S and RJ formats (MSB aligned) can output as many bits as they want with receiving side not having to know how many there really are. If a device outputs 32bits and the DAC can only do 16, it can and it will still sound as good as DAC can do without any explicit knowledge about how many bits were being output, since it captures highest bits first and ignores any lower ones. Unfortunately japanese seemed to have hated these formats...

Because of this, you cannot just put the 18bit DAC into a thing that was using 16bit one, while the DAC is confed to 18bits. TC6116AF based devices can output either 16 or 18 bits, depending on software conf, so in theory it is possible to do the upgrade if software gets hacked to enable the right kind of output.

RichB93 wrote on 2024-05-11, 23:41:

Just had a look and it uses the UPD6736 DAC which itself appears to be the 16-bit only baby brother of the UPD63200. It's pin-compatible, with the only difference being that pin 3 that selects between 16/18-bit on the UPD63200 is not connected on the UPD6736. I imagine you could 'upgrade' it if desired, but to be absolutely honest I've struggled to hear any difference between my MT-120 and my SC-55ST, and looking at the spec sheets between the two chips shows very little difference in performance characteristics.

Ah, interesting. So it uses the lower quality version. It's 6376, not 6736, btw. A couple SC variants use it, although the original 55 uses the 6379 (not sure what differences exist between 6/9).
Generally speaking the UPD63200 is highly regarded, it's in the JV-1080 which people love the sound of.

The SC-55ST doesn't use the UPD63200, it uses the UPD6379, same as the SC-55, and presumably very close to the 6376. So it's definitely expected that they would perform similarly.

One interesting point from comparing the datasheets was how much lower the noise rating is for the 18-bit chip, about 5dB less noise, crosstalk, distortion and improved dynamic range.

Interestingly, looking at the 6376, it looks like it might outperform the 6379, but they are extremely close, with the 63200 a bit better than either.

6379 is the lowest cost version, and its main issue is both channels use same VREF internally and it increases stereo crosstalk and distortion a little. 6376 and 63200 also have separate analog and digital power rails which helps to improve performance even more compared to 6379.