Tag Archives: M5Stack MIDI

M5Stack U187 General MIDI module

Posted on by

Getting right to the point, cabling the M5Stack U187 MIDI Unit was a straightforward breeze. I now have a tiny General MIDI (GM) module for less than $50 USD. Best of all, the audio is cleaner than other SAM2695 implementations and I have full access to the Roland GS-compatible engine within.

Yep, I traced out signal paths to make sure +5V and ground go to the right places. M5Stack have done a good job with their connector and port layout. Plus, the cable color-coding makes it easy to see “what goes where.”

M5Stack U187 General MIDI module cabling

The picture above (click to enlarge) shows all of the electronics and cabling splayed out. I added an in-line power switch between the AC-DC adapter and the M5Stack buck converter. The only “trick” is to jumper the RXD and TXD signals. The jumper creates a signal path from the external MIDI IN to the SAM2695 MIDI port. RXD and TXD are both TTL-level signals, i.e., the receive side is after the opto-isolator.

And, gosh, M5Stack gear is inexpensive for what ya get. I’m tempted to try one of their integrated controllers like the M5Stack Core 3. Count me in.

Next on the agenda is a case. I’m going to stuff everything into a plastic Hammond 1591CSBK, also known as a “guitar pedal” case. I don’t intend to add connectors; the audio, MIDI and power switch cables will dangle out of the box. I’m ham-handed when it comes to craftsmanship and there is no reason to complicate set up. I will use a CME MIDI cable since the CME’s have much smaller plugs. The HOSA MIDI cable (above) won’t fit inside the 1591 case.

The only quibble is that M5Stack have jacks on all four sides of the U187 module. Thus, I’ll need cables with compact, right-angle plugs.

Overall, the M5Stack U187 MIDI Unit is the fastest, cheapest path to a GM tone module. Recommended.

Copyright © Paul J. Drongowski

Sound test: Yamaha A50 vs. SAM2695

Posted on by

The Yamaha A50 keyboard and the M5Stack U187 MIDI Unit (synthesizer) are based on two different ultra-low cost chips: the Yamaha SWLL (YMW830) and the Dream S.A.S. SAM2695, respectively.

The SAM2695 implements the full General MIDI (GM) sound set replete with Roland GS control and System Exclusive (SysEx) MIDI messages. The A50 implements forty voices from the GM sound set and a subset of the Yamaha XG MIDI standard. Because the A50 is a subset, it seems only fair to compare equivalent voices and see which synth is stronger.

The table at the end of this post is a voice-to-voice comparison. Neither instrument will have you ditching your Montage or Kronos. 🙂 The price points are definitely entry-level — $120 USD for the A50 (if can find one) and $15 for the M5Stack U187 MIDI Unit.

Surprisingly, the main grand piano voices are nearly identical! Both pianos are single strike and key velocity simply makes the underlying multi-sample louder or softer. Unexpectedly, the A50 electric grand is darker than the main grand. I prefer the darker tone as it is less likely to shatter glass.

The A50 electric pianos correspond to dark Rhodes and FM DX tones. The SAM EP has a bell-like chime, even its attempt at Rhodes.

The organs aren’t going to knock you out being the typical GM fare. The A50 drawbar organ has more low-mid tone and guts. The SAM rock organ is annoying and is especially buzzy in the low end. (An attempt at overdrive?) It’s unusable.

The A50 acoustic guitars have more mid-range body tone. The SAM clean and overdriven electrics are thin and the SAM overdrive (OD) is unconvincing. I selected A50 voices through its front panel and Yamaha may be adding the chorus effect to the clean guitar. Both jazz guitars need chorus to get the classic JC120 effect.

The SAM basses sound like a sampled electric. The SAM acoustic bass is not very jazzy (authentic). The A50 slap bass nails “Seinfeld” and the A50 synth bass almost nails “Chameleon”. The SAM synth bass is all punch and no sustain — doesn’t sound very rezzy.

The SAM solo violin and cello have more attack and body than the A50. Didn’t see that coming! The SAM pizzicato string voice has reverb sampled in, resulting in playback artifacts. The A50 harp low notes are unrealistic.

My biggest knock against SAM is the ensemble string voice. There is a bad, very audible loop lump in the octave about middle C. This gaffe should have never shipped.

Trumpet and trombone are what one would expect of GM solo brass — kind of real, but one-dimensional. Again, it’s a single multi-sample made louder and software by velocity. The A50 French horn is mellower than SAM. The SAM brass section sounds like a sampled synth brass patch, not real horns.

The A50 tenor sax is breathy although it won’t fool anyone. The SAM tenor sounds like a snake-charmers reed recorder. Yuck. I prefer the warmer A50 oboe. The clarinet and flute voices are nearly identical.

What can you say about synth leads and pads? They are what they are. The A50 has a few nasty, aggressive lead voices and the SAM has a few, too. Yamaha nails a few of the classic GM synth voices, but they were there at the beginning of General MIDI, weren’t they? 🙂

Overall, it’s a split decision. I lean Yamaha A50 over SAM2695. Yet, I keep repeating “15 dollars” over and over again. Remember, SAM is a full GM sound set and you might be able to substitute an alternative GM voice in place of a weaker voice.

If you like Akai MPK Mini and want an A50-like experience, I recommend the Akai MPK Mini Plus 37 combined with the M5Stack U187 MIDI unit. The M5Stack gives you a complete GS-compatible synth module (for $15!). Avoid the Akai Mini Play and its brain-damaged SAM implementation.

Copyright © 2025 Paul J. Drongowski

+ mark means "generally useable for a low-price instrument"

PC1  Voice name            A50 SAM  Comments
---  --------------------  --- ---  --------------------------
1    Grand Piano            +   +   Same
3    Electric Grand Piano   +       SAM: bright; A50: dark
5    Electric Piano 1       +       SAM: chimey tines; A50 dark Rhodes
6    Electric Piano 2           +   SAM: Rhodes; A50 DX EP

12   Vibraphone             +   +   Same
13   Marimba                        SAM: more hammer tone

17   Drawbar Organ          +       A50: more low-mid freq
19   Rock Organ             +       SAM: sampled chorus is annoying, buzzy
22   Accordion              +       SAM: thin; A50: chorus/octaves
23   Harmonica                  +   A50: thin

25   Nylon Guitar           +       A50: body tone/resonance
26   Steel Guitar           +       A50: body; SAM: not bad!
27   Jazz Guitar            +   +   A50: dark; SAM; bright; both need chorus
28   Clean Guitar           +       SAM: thin; A50: built-in chorus, sustain
30   Overdriven Guitar      +       SAM: too clean, OD fake-y

33   Acoustic Bass          +   +   SAM: sampled electric?
34   Finger Bass            +       SAM: picked bass?
37   Slap Bass              +       SAM: picked fretless? A50: Seinfeld
39   Synth Bass             +   +   SAM: no sustain; A50: Chameleon

41   Violin                     +   SAM: more attack, body
43   Cello                  +   +   SAM: more body
46   Pizzicato Strings      +       SAM: sampled reverb, artifacts
47   Orchestral Harp            +   A50: low notes unrealistic
49   Strings                +   +   Similar; SAM: Can hear loop point

57   Trumpet                +   +   SAM: slightly warmer; A50: more real
58   Trombone               +   +   A50: more attack blat
61   French Horn            +   +   SAM: brighter, more attack; A50: mellow
62   Brass Section          +       SAM: sampled synth brass?
63   Synth Brass                    Very similar

67   Tenor Sax              +       A50: breathy; SAM: snake charmer
69   Oboe                   +       SAM: bright, almost synthetic
72   Clarinet               +   +   Very similar
74   Flute                  +   +   Very similar

81   Square Lead                    A50: pure; SAM: nasty, chorus/distort
82   Sawtooth Lead                  A50: clean; SAM: nasty, chorus/detune
83   Gemini                         A50: nasty; SAM: Calliope
85   Punchy Chordz          +       A50: nasty; SAM: kind of weak

89   New Age Pad                    SAM: bell-like; A50: classic GM
90   Warm Pad               +   +   Both good; A50: classic GM
101  Brightness                     What can I say?

M5Stack U187 MIDI in the house

Posted on by

Here are a few pictures of the M5Stack U187 MIDI unit, U125 buck converter and cables.

M5Stack MIDI Unit and 5V buck converter

These M5Stack parts are tiny. I included an SD-sized adapter in one of the pictures in order to convey a sense of scale.

The M5Stack modules interconnect by way of 4-pin JST connectors (GROVE). I plan to use the U187 MIDI Unit as a standalone MIDI module powered by the 5V buck converter and an AC adapter. The buck converter requires a center-positive adapter cable, by the way — a simple fact not mentioned in the converter’s description.

The U187 MIDI Unit has MIDI IN on 5-pin DIN and 3.5mm jack. It has MIDI OUT on 5-pin DIN and 3.5mm jack. The slide switch controls internal signal flow. Optionally, one can pass the MIDI IN through to the MIDI OUT as shown in the routing diagram.

The next step on the way to musical joy is figure out the wiring. The short ribbon cables are “unbuckled”, a term which I have not encountered before! “Unbuckled” seems to mean straight-through. In other words, when you look at the JSTs in the same orientation, pin 1 is white on both, pin 2 is yellow on both, etc. Conceivably, one could have a “twist” that reverses the signal order.

Why worry, Alfred? The buck converter has a JST connector, too. The +5V and Ground pins are live while the two “data” signals are unconnected (NC). I plan to short the U187 TXD and RXD signals, and when push comes to shove, I do note want to accidentally short +5 and Ground!

M5Stack color-code their JST ports, thank goodness. The U187 port is blue and matches the blue PORT.C UART JST on their controllers and bases. This should help me do the matchy-matchy when wiring. I plan to double-check power using a multi-meter. It’s not the expense ($15) of blowing up the U187 as much as the time wasted ordering a replacement and waiting on delivery.

One Dream SAM tidbit. Dream have formally declared the SAM 2000 series synth chips as end of life (EOL). The window for final orders has already closed. Dream have asked customers to move on to the SAM 5000 series.

M5Stack U187 MIDI Unit inside

The image above shows the inner guts of the M5Stack U187. The U187 case is held together by a tiny hex screw and lucky me, my smallest hex wrench got the job done. You see the Dream SAM2695 in the shot. Long live the 2000 series!

Copyright © 2025 Paul J. Drongowski