imi wrote on 2021-02-12, 12:19:

is there any listening example of the differences between the old old one and the old rev.1?

Here you can hear the difference with the credits track of Dune II.

Hmm, to re-iterate, CM-32L has nothing to do with "old rev.1".

yeah let me repeat that to be more clear ^^
I was wondering about the difference between:
OLD Roland MT-32 up to serial number 851399
OLD Roland MT-32 revision 1 serial numbers 851400 - 950499

I believe there are none. As long as the control ROM version is exactly the same, no audible differences should be observable. But of course, each and every unit sounds uniquely having been aged 😀

I believe the best combination is a Roland MT32 (old unit) and a Roland CM32L / CM64 / LAPC-I.

NewRisingSun wrote on 2021-02-12, 19:36:

OP is asking about two versions of "old-type" MT-32 (ASSY 7937731000 vs. ASSY 793741000), not about "old-type" vs. "new-type" (ASSY 7937731001) MT-32.

All that the later "old-type" MT-32 changes is to consolidate the circuit board design by changing the package type of the LA32 chip and by replacing EPROMs with mask ROMs. Control and sample ROM content are identical by all accounts. See the MT-32 Service Notes Second Edition.

These ASSY numbers are not too intuitive with the MT-32s it seems. I have one with ASSY 7937731001 which supposed to be the "new-type" MT-32, however it is missing the headphone jack, and the PCB layout looks exactly like the "old-type", except it already has the QFP type LA32 chip. Also, it has the old v1.7 ROM version instead of v2.0.
Indeed, per Service Notes 3rd edition :

https://i.imgur.com/qhkI36B.png

So it seems the real differentiator between the "old-type" and "new-type" MT-32 is the existence of the headphone jack (i.e. completely redesigned PCB), rather than the ASSY number itself.

I find the "old type" MT-32 most suitable as well.

Although I have both the MT-32 as well as a CM-32 (and a CM-500 for that matter), all of those are stored away for years to come probably, I must admit I am more than happy to use serdaco's MT-32 Pi HAT with MT32Pi. Saves a lot of deskspace as well and even with a half decent SC-55 soundfont I find this one little device sufficient to cover all my DOS gaming needs for the time being.