MT-32 vs. CM-32 et al.

[Rhizome]

Perhaps I should say here - I just bought a Roland CM-32L on EBay for £30 (it was buy it now, no way could I resist!) 

So now I have the MT-32 and CM-32L - like many say, always good to have a spare 

[Cloudschatze]

No feedback regarding the VCA stuff...?


Here are some other things I noticed while looking into it:

In an 01 MT-32/CM, the default master volume setting is based on the position of the rotary encoder, whereas the 00 MT-32 defaults to 100.

In just the 01 MT-32, circuit traces exist for an analog output connector before the VCA in the signal path.

The LAPC-I has a row of four "holes" along the top of the card: RXD, TXD, L and R. (TXD has a wire loop installed.)
RXD and TXD are MIDI I/O, directly tied to the P8098 CPU. According to the schematic, if you were to send a data request to the LAPC, you would be able to read the reply via the TXD. (This isn't possible otherwise.)
L and R are the left and right analog signals that combine immediately following the S/H chips. (Thereby bypassing the amplification stages.)



Finally, the answer to all of the crackling/distortion issues, direct from the MT-32 manual:

MASTER VOLUME
*If the sound is distorted, lower the volume.

VOLUME FOR EACH PART
*Keep the volume for each part low enough to avoid overloading or noise interference.

See! It's really the musician's fault!

[Tom]

MASTER VOLUME
*If the sound is distorted, lower the volume.

VOLUME FOR EACH PART
*Keep the volume for each part low enough to avoid overloading or noise interference.

I can't believe I've never seen that!   

[Laust]

No feedback regarding the VCA stuff...?

Does the VCA circuit replace the function of the muting circuit in the CM/LAPC-I/MT-32 rev1?  If I look at the CM-64 schematics, there is a muting circuit but it seems its output is only sent to the PCM portion of the synth (I didn't have time to open up the CM-32L yet, so for all I know, it could be present only in the CM-64). In the original MT-32, the muting circuit is moderately succesful at muting the audio during power up and power down, when voltages fluctuate and you can get loud noise spikes on the output. With the VCA in place, the CPU would be able to mute at least part of the analog circuitry. As I recall, the CM-32L isn't as loud/noisy on startup/shutdown as the old MT-32 either.

Also, I can't see traces for analog outputs before the VCA in the MT-32 rev1. Where are they supposed to be? There's an unused connector (CN8), but it only has two pins and one of them is ground. Not enough to carry the audio signal. CN9 further way appears to be tied to ground completely.

In an 01 MT-32/CM, the default master volume setting is based on the position of the rotary encoder, whereas the 00 MT-32 defaults to 100.

It's a high quality pot, not a rotary encoder

[Cloudschatze]

Does the VCA circuit replace the function of the muting circuit in the CM/LAPC-I/MT-32 rev1?

No, these synths all have a muting circuit, in addition to the VCA.

If I look at the CM-64 schematics, there is a muting circuit but it seems its output is only sent to the PCM portion of the synth (I didn't have time to open up the CM-32L yet, so for all I know, it could be present only in the CM-64).

It looks like the output from the LA muting circuit might be responsible for control of the muting circuit on the PCM board?

In the original MT-32, the muting circuit is moderately succesful at muting the audio during power up and power down, when voltages fluctuate and you can get loud noise spikes on the output. With the VCA in place, the CPU would be able to mute at least part of the analog circuitry. As I recall, the CM-32L isn't as loud/noisy on startup/shutdown as the old MT-32 either.

I noticed that the muting circuit in the 00 MT-32 isn't tied to the CPU, whereas it is in everything else. I wonder if this might be part of the reason for it working better in the later models.

The VCA isn't being used for muting, else the headphone jack (which isn't connected to the muting circuit), might not pop so badly.

Also, I can't see traces for analog outputs before the VCA in the MT-32 rev1. Where are they supposed to be? There's an unused connector (CN8), but it only has two pins and one of them is ground. Not enough to carry the audio signal. CN9 further way appears to be tied to ground completely.

Yep, CN8. From what I can tell, R19 or R21 will complete the circuit, for either right or left channel output. I can't think of a use for this beyond testing purposes.

In an 01 MT-32/CM, the default master volume setting is based on the position of the rotary encoder, whereas the 00 MT-32 defaults to 100.

It's a high quality pot, not a rotary encoder

Yeah, yeah.

[Rhizome]

In an 01 MT-32/CM, the default master volume setting is based on the position of the rotary encoder, whereas the 00 MT-32 defaults to 100.

My MT-32 doesn't appear to default to 100 on startup. It defaults to where ever I leave the master volume knob on, yet I have a first generation model (like I said, 1.06 ROM version).

[Cloudschatze]

In an 01 MT-32/CM, the default master volume setting is based on the position of the rotary encoder, whereas the 00 MT-32 defaults to 100.

My MT-32 doesn't appear to default to 100 on startup. It defaults to where ever I leave the master volume knob on, yet I have a first generation model (like I said, 1.06 ROM version).

Guess I didn't test that very well.

On my 00 MT-32, if the volume pot is turned all the way to the left or right, the master volume will read 100 when powered-on. It seems that the pot goes below the resistance necessary for the zero value, and, for whatever reason, the system decides that these sub-values should result in the 100 setting. If, while powered-on, I turn the volume knob down until it reaches zero, and no further, then, if I power off/on, it will still be be at zero.

This might be potentiometer specific, varying between units - I'm not sure. My 01 MT-32s don't exhibit this behavior.

[Tom]

Ditto for my 00 MT-32; doesn't matter what the Master Volume says the volume is, or where the dial is, the volume level is still at 100 when powered ON.

[Cloudschatze]

Ditto for my 00 MT-32; doesn't matter what the Master Volume says the volume is, or where the dial is, the volume level is still at 100 when powered ON.

The analog volume, yes, but the "digital volume," or the output from the LA32 chip, should still be variable, based on the Master Volume setting.

Tom, are you saying that, with your MT-32, a Master Volume of say, 10, will sound the same as a setting of 80 during playback? Or have I misunderstood?

[Rhizome]

On my 00 MT-32, if the volume pot is turned all the way to the left or right, the master volume will read 100 when powered-on.

Ah, now that does happen with mine. First time I powered it on when it arrived it was all the way to the left and shown "100" on the screen 

[Tom]

Tom, are you saying that, with your MT-32, a Master Volume of say, 10, will sound the same as a setting of 80 during playback? Or have I misunderstood?

No...

I'm saying that, when I power ON the MT-32, the output level is 100 by default, even though the Master Volume dial may be set to a lower position -- and the display might read 82.  The display doesn't show "100" when powered ON, but the output IS 100.   As soon as I turn the Master Volume dial, it adjusts properly to the desired level and number value. 

[Cloudschatze]

My 00 MT-32 (ROM ver. 1.07) seems to behave properly. When powered-on at a "low" rotary setting (other than hard left), the output is appropriately low, and when high, the output is likewise high. What ROM version do you have, Tom?

[Rhizome]

My Roland CM-32L arrived this morning, all working 

One thing I have noticed compared to the MT-32 is it appears to clip easier.

Anyone else noticed this?

[NewRisingSUn]

Yeeeees.



That's we've been talking about on the whole last page of the thread or so.

[Rhizome]

Yeeeees.



That's we've been talking about on the whole last page of the thread or so.

Sorry, I haven't been reading very well then 

[Tom]

What ROM version do you have, Tom

I forgot how to check...what's that magic key combo again? 

[Caliburn]

What ROM version do you have, Tom

I forgot how to check...what's that magic key combo again?

You hold down the Part 4, Rhythm, and Master Volume buttons when you power up.

-Luke

[Tom]

v1.07 10Oct87