I want to give a shout out to Lionel on the PSR Tutorial Forum. He posted a very nice PSS-A50 mod — stereo!
Yep, the PSS-A50 is stereo and, as Lionel discovered, the in-built samples are also stereo. Check out Lionel’s PSS-A50 stereo mod video. His video begins with a great close-up of his changes to the PSS-A50 digital main board (DM).
As noted in my PSS-A50 look inside, the central computer and tone generator is Yamaha’s SWLL processor (YMW830-V). The SWLL is a system-on-a-chip (SOC) which integrates the host CPU, working memory, key/display scanner, and tone generator. Just add a 37-key keyboard, display driver, 2MByte serial flash program/waveform ROM, USB controller, audio electronics and power electronics, and you have a complete ultra-low cost synthesizer.
The digital-to-audio converters (DAC) are integrated into the SWLL. The SWLL has six DAC-related pins:
DACLPP (pin 1)
DACLMM (pin 2)
DAC_VDD (pin 3)
DAC_VSS (pin 4)
DACRMM (pin 5)
DACRPP (pin 6)
DAC_VDD and DAC_VSS are conversion reference voltages. DAC_VDD is derived from DAC_VCC produced by a low drop-out voltage regulator (Texas Instruments TLV74333PDBVR). DAC_VSS is ground.
Yamaha SWLL (YMW830) DAC signals
DACLPP and DACLMM are differential audio signals for the left channel. DACRPP and DACRMM are differential audio signals for the right channel. DACRPP and DACRMM are left unconnected in the PSS-A50. There are two test points, DACL- and DACL+, on the printed circuit board (PCB), in case you would like to probe these signals.
PSS-A50 post-DAC low pass filters
DACL+ and DACL- feed two operational amplifiers which are low pass filters. The low pass filters produce signals LOUT+ and LOUT-, which are sent to the plus and minus inputs of the headphone amplifier (TPA6132A2RTER) and speaker power amplifier (Rohm BD27400GUL). It’s differential audio signals all the way, presumably, to keep noise low.
The Texas Instruments TPA6132A2RTER is a 25 mW stereo headphone amplifier. The Rohm BD27400GUL is a low voltage class-D monaural speaker amplifier.
I have to admire Lionel’s construction skills as it is quite difficult to solder wires to a surface mount IC. Nice work replicating the stereo low pass filters, too.
Keep the Yamaha PSS-A50 hacks coming! Please don’t forget the PSS-A50 MIDI mod.
Here are some additional Yamaha PSS-related stories:
Here’s a look into the past — and maybe, the present.
A PSR Tutorial Forum member inquired about the chorus effects in the PSR-E463. The PSR-E463 has the usual system chorus effect and the newer DSP chorus effect. I’m going to focus on the older system chorus effect.
The PSR-E series chorus system effect date back to the earliest days of Yamaha XG and arranger keyboards. These are low-cost entry-level keyboards and usually contain a single integrated circuit (IC) which integrates the main processor (CPU), tone generator and effect units. The most price- and cost-sensitive models integrate the wave memory (samples) on the IC, e.g., the SWLL (PSR-F51). Processors in the other models have an external wave memory, e.g., the SWL01 (PSR-E443) and SWX03 (PSR-E463).
Newer DSP effects aside, the E-series models share the same basic reverb and chorus effects. There are three chorus effects:
Chorus1 (MSB: 66 LSB: 17)
Chorus2 (MSB: 65 LSB: 02)
Chorus3 (MSB: 65 LSB: 00)
The LSB has varied, but they all refer to the same CHORUS (CELESTE) effect algorithm. The LSB just selects a set of preset effect parameters. Chorus1, BTW, falls into the XG CELESTE category, not CHORUS.
Due to hardware integration, the chorus effects likely share the same hardware. Since none of these processors have external DSP RAM, the chorus memory is integrated, too.
As far as chorus is concerned, this is the way it has been since the 1990s! Let’s look back to the Yamaha QY-70 XG implementation (1995). I suspect that the current chorus effects are the same or very similar to the good old QY.
The QY-70 had one chorus and celeste effect algorithm:
Param# Parameter Value range ------ ------------------- -------------------- 1 LFO Frequency 0.00Hz - 39.7Hz 2 LFO PM Depth 0 - 127 3 Feedback Level -63 - +63 4 Delay Offset 0 - 127 5 6 EQ Low Frequency 50Hz - 2kHz 7 EQ Low Gain -12dB - +12dB 8 EQ High Frequency 500Hz - 16.0kHz 9 EQ High Gain -12dB - +12dB 10 Dry/Wet D63;gt;W - D=W - D<W63 11 ... 15 Input Mode Mono, Stereo 16
These parameters are laid down by the Yamaha XG specification.
The XG specification does not define the preset values, however. Here are the QY-70 preset chorus values:
QY-70 Chorus3 has the same MSB/LSB as PSR-E Chorus2. QY-70 Chorus 1 has the same MSB/LSB as PSR-E Chorus3. Confusing? Yes, but these are probably the PSR values or close to it.
None of the QY-70 presets have the same MSB/LSB as PSR, so your guess is as good as mine.
Now, the really bad news. The PSR-E series, at best, is XGlite. XGlite implementations typically don’t support the XG messages that set effect parameters. Therefore, what you hear is that you get. In other words, the effect presets are hardwired.
The Yamaha PSS series with its minimal SWLL processor implements exactly one chorus and exactly one reverb preset. You get what you pay for!
Yamaha PSS-A50 top and bottom [Click images to enlarge]
The A50 has two main boards: the digital and analog electronics board (DM) and the front panel board (PN). After removing nine screws — don’t forget the screw hidden in the battery compartment — the A50 splays into two halves: the bottom half containing the battery compartment, DM board and keybed, and the upper half containing the speaker and PN board. The battery connects to a JST XH connector on the DM board. Ribbon cables connect the keybed and the panel board to the DM board.
Yamaha PSS-A50 front panel board (PN)
The PN board has traces for the front panel buttons. The buttons are arranged into a 3 by 8 switch matrix: 3 drive lines and 8 sense lines. The power Standby/ON switch has two dedicated lines. The eight sense lines are shared with the three digit LED display. A further 3 lines are devoted to the display (for a total of eight lines). In addition to the front panel switch matrix, the PN board conducts audio signals to the speaker through two wide PCB traces.
I dare to say that the A50, PSS-E30 Remie and PSS-F30 have the same panel board. Only the front panel graphics and software differentiate the models in that regard.
Yamaha PSS-A50 main electronics board (DM)
The DM electronics board is tiny and is packed with surface mount (SMT) components. Impressive! The main digital components are:
Yamaha YMW830-V: Processor and tone generator (IC101)
Winbond 25Q16JVS1M: 16Mbit Serial flash memory (IC102)
74VHC273: 8-bit latch for display data (IC301)
NXP LPC11U13F/201: USB interface (IC401)
The YMW830-V is also known as “SWLL” and is a Yamaha proprietary system on a chip (SOC). The A50 has separate amplifiers for the speaker (IC701) and headphone output (IC601):
TI TPA6132A2RTER: Headphone amplifier (IC601)
Rohm BD27400GUL: Mono class-D power amplifier (IC701)
NJR NJM2740M: Dual operational amplifier (IC501)
The dual operational amplifier is part of the post-DAC low pass filter. Finally, the power-related components are:
TI TLV74333PDBVR: 3.3V regulator (IC001)
TI TPS63060DSCR: Switching regulator (IC004)
TI TPS25200DRVR: 5V eFuse/power switch (IC006)
The A50 must choose and switch between +5V USB power and battery power. That’s the role of the eFuse/power switch component.
Yamaha PSS-A50 USB interface (NXP ARM MCU)
The NXP LPC11U13F is a bit of a surprise to me. It is an ARM Cortex-M0 32-bit microprocessor (MCU) with 24KB of flash memory. The SWLL sends and receives MIDI through its UART RX/TX ports. The ARM LPC converts simple MIDI from the SWLL to MIDI over USB. Using an ARM MCU to do the job seems like over-kill. It goes to show how far we have come as an industry when an MCU can be dedicated to such a mundane task!
Yamaha PSS-A50 CPU (Yamaha YMW830-V SWLL)
The SWLL (YMW830-V) has many of the specs that we’ve come to know about Yamaha’s entry-level CPUs. The external crystal resonates at 16.9344MHz. The SWLL internal clock is 33.8688MHz and generates a 67.7376MHz master clock. If these numbers look odd to you, simply note that they are even multiples of 44,100Hz, the basic sample rate:
67.7376MHz = 44,100Hz * 1,536
When an external DAC is used, the master clock provides the bit serial audio clock. 1,536 can be subdivided in all sorts of interesting ways depending upon sample word length.
The SWLL integrates host CPU, memory, tone generation, serial MIDI communication, keyboard and front panel scan ports, and display ports. The digital to analog converter (DAC) is also integrated into the SWLL. The SWLL is truly Yamaha’s low-cost system on a chip solution.
The SWLL loads its software and samples from a 16Mbit serial flash ROM. 2MBytes for software and samples is not much, so one wonders if the SWLL has a preprogrammed flash memory of its own?
With the exception of the ARM LPC chip, the A50, PSS-E30 Remie and PSS-F30 electronics are identical. The software and samples determine the product personality. Such a high degree of commonality allows Yamaha to manufacture PSS keyboards (in India) and sell them at a dirt cheap price. Hats off — the amount of technology at this price — less than $100USD — is simply astounding.
The Yamaha PSS series keyboards are inexpensive, entry-level instruments which are super lightweight, battery powered, portable and fun. The PSS line is like a small group of fantasy characters where each character has its own super-powers.
PSS-E30: A musical game keyboard for younger kids.
PSS-F30: “Honey, I shrunk the arranger” keyboard for people who want to play songs with an accompaniment.
PSS-A50: A phrase-based music machine which records and speaks MIDI over USB to your DAW or other computer- or table-based music applications.
Last year, I reviewed the Yamaha PSS-E30 Remie and passed it along to our grandson as a Christmas gift. Remie is suitable for young kids, but even Mom and Dad have fun with the musical games.
Yamaha PSS-A50 keyboard [Click to enlarge]
The PSS-A50 (henceforth “A50”) is aimed at people who want more flexibility than the fixed accompaniment styles in the PSS-F30. The A50 has 138 musical phrases — “arpeggios” in Yamaha-speak — that drive an in-built arpeggiator. Twenty-two arpeggios are drum patterns; the rest of the arpeggios are melodic, covering both instrument-specific riffs (strums, bass lines, chord comps) and general purpose phrases like up/down broken chords, etc.
Experienced Yamaha players have seen these arpeggios before. In fact, the A50 reminds me of the Yamaha Synth Arp & Drum Pad iOS application. Without getting into the details, you select a voice, select an arpeggio (“arp”), enable the arp, hit record, and go. If you check out Yamaha’s YouTube tutorials, you’ll see how easy it is to get started.
At this point, I suggest watching Keen On Keys excellent video. It covers all the basics, a brief teardown, and more. I won’t go into such details here. (This chap did a terrific job!) I learned quite a lot from this video including basic “how to use it” information.
Oh, how I long for such reviews in Electronic Music (once Keyboard mag), once again. Ken Hughes, where are you? After reading one of those old product reviews, you actually knew a little about playing the instrument. Now, pfffft!
The sounds
Let’s get down to brass tacks. Like Remie, you won’t get Yamahas top sounds. Shucks, it’s only $100 USD (street price).
Truth be told, even though I regarded the A50 as a candidate for mod projects, I wasn’t too wild about the sounds that I heard in on-line demos. I was hesitant to buy one. Once I got the A50 under my fingers, however, I warmed up.
Basically, the A50 and Remie samples and synth engine are at the same level. The A50 adds touch sensitivity and that, I suspect, makes the difference. Sure, the piano (for example) is uni-dimensional and you can hear it play the same sample louder or softer depending upon strike velocity. The overall effect is more musical, however. Weird how that works?!
The A50 audio OUT is mono. Reverb seems to be the only system effect. Even Yamaha’s cheapest chip implementations have chorus, so it may take a little MIDI magic to unlock that door. The whole sound can be sweetened by out-board effects like maybe a guitar pedal (e.g., TC Electronic Hall of Fame reverb) or a spatializer. I slung an A50 beat through the Korg Volca Mix stereo width and compression effects and got a rather nice result. The Volca Mix Hi/Lo Cut let me isolate the tops and kick, too. I strongly recommend adding external effects.
The A50 motion effects let you juice up your performances. I’m still exploring the motion effects and I’m glad to have them. The motion effects add a way to vary the sound during performance, avoiding a uni-dimensional sound. You get filter fun, pitch bends, slicing and all sorts of sonic mayhem. A few effect types would be good for Hawaiian pedal steel. 🙂 It would be nice to leave the auto wah ON in order to play two-handed funk — a small quibble.
The A50 size, features and price invite comparison against the Yamaha SHS-300 and SHS-500 Sonogenic. Unless you really want the keytar format, I don’t see the value in the SHS-300 versus the A50. I will bet dollars to donuts that the SHS-300 is based on the same chip and samples as the A50. Personally, phrase recording is more fun and creative than a pretend, low-budget, cheap build keytar. Speaker quality is probably a wash between the two and the A50 puts out 1.5W versus 0.7W.
The A50 against the SHS-500 is another story. The SHS-500 voices are definitely better quality. Although the SHS-500 LINE OUT is mono, you can look to its PHONE OUT for stereo. The SHS-500 has PSR E-series DSP effects, three forms of MIDI (USB, 5-pin, and Bluetooth), a General MIDI sound set (available via MIDI only), and jam mode integration with Chord Tracker. The SHS-500 beats the A50 on sound. On the other hand, I prefer the A50’s speaker versus the SHS-500. Of course, the SHS-500 is mainly for playing and doesn’t have an arpeggiator or recorder.
Build quality
One big factor is build quality. The SHS-500 is a solid instrument. The SHS-300 and A50 are cheap. Even though Yamaha specs call out “37 HQ (High Quality) mini keys” for all three keyboards, only the SHS-500 is up to the same quality as the Yamaha Reface series. Yamaha marketing may claim otherwise, but you can feel the difference. The Reface and SHS-500 will stand up to abuse — the SHS-300 and A50, not so much.
As to A50 build quality, the electronic boards and cabling look up to snuff. EMI shielding is absent. Audio quality on battery power or external USB power adapter is good and is reasonably quiet. Powered by my HP desktop, the A50 is susceptible to digital schmutz and produces loud noise through its audio out. One could put blame on the desktop, but nearly all computer switching power supplies are dreadfully noisy. USB powered instruments need better filtering on USB power rails.
In use
I want to use the A50 as a looper: put down a rhythm line and a bass, then jam. It takes a little bit of practice to make glitch-free loops. I wish the A50 applied “measure quantize” to recordings, that is, trim recordings to a clean measure timing boundary. Right now, you have to turn off recording by feel and hope you get it right.
While horsing around with MIDI (another subject for another day), I noticed that the A50 has four parts, each on its own MIDI channel:
Keyboard voice: Live, real time performance (Default: channel 1)
Arpeggio sequence: Live, real time arpeggiation (Default: channel 2)
Recorded keyboard: Recorded keyboard performance (Default: channel 3)
Recorded arpeggio sequence: Recorded arpeggio (Default: channel 4)
Hmmm, this makes me wonder if I can layer up to four parts? So far, I can layer 3 distinct musical parts. The fourth part is still elusive.
The main problem is no overdub. It is possible to record two parts at once: arpeggio plus keyboard performance. Thus, you can lay down a drum pattern (arpeggio) and a bass line (by hand). Then, loop the playback and play over the top. Seems like I should be able to add a live arpeggio to the stack.
Play the bass line over the drum pattern. Start playing in time with the drum pattern.
Press REC to stop recording.
Turn the arpeggiator OFF.
Select a piano voice (e.g., voice 2).
Press SHIFT+PLAY to start a looping playback.
Jam over the playback.
Press STOP to stop playback.
Recording doesn’t start until you begin to play the bass line. That locks the bass to the drum pattern. You need to stop recording just before the next loop iteration begins.
If you need some jazzy chords, try: GM7/E, Fm7/B, FM7/D, Em7/A (also notated as Em9, Bm11, Dm9, Am11).
Doggone it, seems like I should be able to layer live arpeggiator into that mix! I’ll keep trying.
Update: Practice makes perfect. Yes, you can get four lines going. I recorded drum and electric piano following the procedure above. With the recorded parts playing, I started a looping bass arpeggio. Finally, I solo’d over the three running parts. Neat, and as complex as you might want for a little practice jam.
Questions
As I begin to explore the A50 MIDI implementation, there are a number of unanswered questions. First and foremost, can I save and restore recorded MIDI data? Does the A50 respond to SysEx messages for reverb and chorus type? Can I drive the A50 with the old Synth Arp and Drum Pad application and make use of its range of arpeggios? Can I load my own simple backing tracks into the A50’s recorder memory?
The final word
After my initial reluctance, I’m glad that I bought the PSS-A50. Apparently, some folks aren’t so happy as A50s turn up as Open Box items quite frequently. Even though $100 is not much, you can save a few extra bucks if you’re willing to buy an open box item. Given the build quality, you might not want to chance it, tho’.
The A50 does not have a full General MIDI sound set. The sound set is close enough for rock and roll, however. Here is an MP3 of the A50 in action (Traffic’s Feelin’ Alright). Wish I could play that piano solo at the end …
Interested in more PSS-A50 content? Check out these posts:
I’m still thinking about Yamaha PSS mods, most notably, the PSS-A50. Open box A50s are coming on the market and I get the itch to modify an A50. I don’t want to buy a brand new unit since I will immediately tear into it with a screwdriver, drill, and worse! 🙂 Here’s a few more thoughts.
After looking at the PSS-E30 Remie teardown, that speaker has got to go. Even without the speaker, I don’t think there is enough room for the Korg NTS-1 as I first planned.
littleBits filter module
Second-besties, I’m considering a littleBits solution. Lots of folks mod the Korg Monotron to get access to its filter, but oddly, they don’t consider the littleBits filter module. I did a few preliminary experiments with the filter and delay modules using the Yamaha SHS-500 Sonogenic as a stand-in for the PSS-A50 sound generator. The filter and delay sound great although I need to add an envelope generator to make the filter quack and bark.
My main concerns at this point are:
Driving littleBits audio without the Microphone module and the Speaker module. Both modules would take up unnecessary space. I’m just don’t know (yet) if regular headphone levels are strong enough for the littleBits 0 to +5 Volt signaling convention.
Physically and electrically securing the littleBits modules to themselves and the A50 chassis.
Finding 5 volt power in the A50 in order to supply the litleBits modules.
Of course, there’s the problem of mounting the littleBits modules so that the controls (potentiometers) poke through the A50 speaker grill.
I investigated the PSR-F50 audio and digital electronics. The PSS audio amp is mostly likely different than the F50. So, I need to get the A50 service manual. The service manual should help me find the +5 Volt rail, too.
I took another look at the Yamaha YMW830-V processor pin-out. The YMW830-V is also known as the “SWLL” processor. It is a system-on-a-chip (SOC) containing the CPU, memory, and tone generator. The SWLL has five pins (TRST, TDI, TMS, TMS, TCK, and TDO) for serial input/output — most likely USB. This doesn’t bode well for people who want to add 5-pin MIDI to the A50 (or other SWLL-based keyboards).
Reface YC key scan matrix
The PSS series, the Reface series and the SHS-500 share the same 37-key keybed. The key switch matrices are similar. They all break the key range into groups of six keys. Each keybed is a 6 group by 6 key matrix with a dedicated group to scan the fourth C key. The PSS and Reface/SHS differ in the number of key contacts as the Reface/SHS are velocity sensitive and the PSS is not. The Reface/SHS have two contacts per key and the PSS has one contact per key. The Reface/SHS have a total of twelve sense lines (2 lines per key) while the PSS has only six sense lines.
6×6 must minimize ribbon cable width or something because Yamaha will subdivide 61 keys into upper and lower banks in order to deploy six keys per group with 6 groups per bank maximum. You’ll see this practice in the synth product line, too. Just sayin’.
The Yamaha SHS-500 and Reface series use the same MIDI I/O dongle. I came across this rather nice diagram (below) of the SHS’s MIDI port. It should help you to whip up a custom cable or two. [Click image to enlarge.]
I made a little more progress delineating Yamaha’s mini-key product lines. The PSS series is built for low manufacturing cost. Thanks to PSS-E30 (Remie) and PSS-A50 tear-downs, we know that the PSS series is based on the ultra-small, relatively inexpensive SWLL (YWM-830) processor.
So, what to make of the Yamaha SHS-300 and SHS-500 keytars?
The SHS-300 shares the same basic spec as the PSS series: 32 voice polyphony, 8cm speaker, only one effect (reverb), no MIDI, no Bluetooth, etc. Sound quality is comparable to the PSS series. I suspect that the SHS-300 is based on the SWLL, too.
The SHS-500, however, has a much better spec: 48 voice polyphony, MIDI and audio over USB, MIDI over Bluetooth BLE, 9 DSP effects, Master EQ, chorus, reverb, etc. A glance at the SHS-500 service manual shows that the SHS-500 has much in common with the current PSR E-series keyboards, including the SWX03 processor.
If I get the time, I’ll write a quick post about SHS-500 internals.
The SHS-500 is definitely a cut above the SHS-300 in build quality, sound, MIDI capability and tweak-ability. I’m sorely tempted to take a bite of the apple. NAMM, however, is fast approaching (16-19 January 2020) and good sense tells me to wait. Yamaha’s pre-show press release promises 75 new products including a new family-oriented home keyboard.
Product personality is determined by the plastic skin/parts, software in the embedded serial ROM, and the addition/absence of the USB interface integrated circuit (IC). There may be a few other minor differences, but it would be difficult to pin them down without the service manuals. Speaking of which, if you start a mod project, I strongly recommend reading the PSR-F50 Service Manual because the F50’s guts are very similar to the PSS series.
Unless you really want the F50 or E30 voices and functionality, the A50 is the best choice for a mod. The A50 has the USB interface IC and the necessary firmware supporting MIDI over USB. The A50 has a higher street price than the other models, but USB MIDI is worth it.
At the 100,000 foot level, there is plenty of empty space inside for a small microcontroller (e.g., Arduino) or sound mangling analog electronics. You could choose to either keep the speaker if you want portable sound or ditch the speaker and go solely with the headphone output to external amplification.
If keep the speaker, you could easily add some sound mangling circuits like a filter or effects. The littelBits filter might be a good start and is certainly small enough to fit in the empty space. Should be easy to tap into battery power as the battery leads are exposed.
If you ditch the speaker, you have a lot more space to work with. I’d be tempted to add the Korg NTS-1 once it’s available. The NTS-1 can process external audio and has digital effects. Previews have given the digital effects high marks. Unfortunately, the NTS-1 is spec’ed 12.9cm by 7.8cm by 3.9cm, which won’t fit directly into a PSS case. A lot depends upon the size of the NTS-1 electronics board. Even if we can’t fit the NTS-1 into a PSS case, the NTS-1 would be a nice complement to the A50.
Without the speaker, one could use the front panel real estate for additional controls. With all of the arpeggios and such, manual control over filtering and effects would be welcome (in addition to the A50’s fixed motion effects).
At the 50,000 foot level, any one of the PSS models could be stripped down for parts. The case and front panel may or may not float your boat, but you could use the shell and front panel for a keyboard project of your own. It would be easy to apply new graphics to the front panel. The front panel buttons are a switch matrix which can be easily mapped out and then scanned by your code. The front panel has a three digit 7 segment display that needs to be multiplexed and driven.
The keybed is quite useful. The keys are affixed to the bottom of the case, so unless you’re reusing the case, too, you probably will need to cut the keybed out of the case, leaving everything as a unit. The keys sit above a printed circuit board (PCB) with the rubberized switch contacts.
Reface YC switch matrix
I’ll make a leap of faith here and assume that it’s the same keybed as Reface. The schematic above is taken from the Reface YC Service Manual. The key matrix has seven select lines (BK0 to BK6) and twelve sense lines (MK10 to MK21). Your software needs to drive one of the select lines and immediately read the sense lines. There are two sense lines per switch for the “lower” and “higher” key contacts. Software can determine key velocity by measuring the time between contact closures for an individual key.
The most tasty enchilada is the digital logic (DM) board. The A50 board, in particular, could form the basis of a USB MIDI tone module. One could add 5-pn MIDI by bridging a 5-pin DIN and the USB micro-B port. The DM board is quite small: 13.5cm by 4.5cm. And clearly, the DM board can be battery powered. Even if you re-housed the DM board and front panel board, you still would get a very compact module.
Modding at the 10,000 foot level gets difficult. There are the usual difficulties tracing signals and soldering surface mount (SMT) devices and signal paths. Even if you strip out the SWLL (YMW-830) integrated circuit, I’m not sure what you would do with it!
Nor am I confident that the firmware can be easily by re-engineered. Yamaha have never documented wave chip internals, so you don’t have much guidance. There isn’t much code — firmware and waveforms reside together in the 2MByte serial ROM. I would guess that the firmware is SH architecture. Even so, reverse engineering would be a difficult task. I have my doubts about repurposing the code. At best, one might be able to add or change the waveforms?
Personally, I’m inclined to go the sound mangling route.
A few more thoughts before closing.
The A50 is not a General MIDI module. If you want a (mostly) GM/XG compatible Yamaha tone module, I suggest the Pocket Miku NSX-39. Also, while stumbling around the web, you might want to check out the Yamaha YMF-825. It’s a 4-op FM chip which Yamaha released for makers.
