Chrisoft::Blog(r#"RBUS-ADAT devlog")

Origins

Funny enough, the origins of this project has nothing to do with -R-BUS or ADAT.

Ideas to build a digital only version of the EDIROL SD-80 surfaced in -early 2023 as an extension to my SD-80 modding plan. Beacuse my SD-80 is -half broken (headphone amp on analog output 1 fried due to my stupidity, -see my second -SD-80 post for how it happened) and I only ever record it through -its digital outputs anyway, I believe I can drastically reduce the -footprint of it by taking out all the analog outputs and removing the -now unused ±15V rail, making the device USB bus powered at the same -time. There was also plans to add a second digital output to the modded -SD-80, however the plan was never finalized, let alone implemented -because of my lack of proper electronics knowledge and soldering skills. -The idea was therefore shelved.

Meanwhile in early 2022, I acquired a Roland XV-5080 (which I still -have a long overdue review to write). I was also only recording that -thing digitally and sometimes felt that wasting the other 3 stereo -outputs is a shame. I did a bit of research and apparently the R-BUS -port on its back outputs all 4 stereo outputs of the synth. Later I -found out there was the DIF-AT and DIF-AT24 that can convert R-BUS to -ADAT which is still fairly common on modern audio interfaces. However -for a small box that doesn’t really do much, asking price for the DIF-AT -is absolutely crazy – every single listing I saw was ~$200. And the -DIF-AT24, which supports 24-bit ADAT output (in contrast to DIF-AT’s -20-bit output), is pretty much unobtainium. So I decided to live with -recording through its S/PDIF output for the time being.

In September 2023, by pure coincidence, I found a listing on ebay of -a chip described as “ADAT optical encoder/generator”, which was the coolaudio -V1401 that later would become the heart of my design. After reading -its datasheet I decided it would pretty much make my SD-80 digital mod -trivial, with the added benefit of carrying both stereo output channels -on a single port. So I opened up the service manual for SD-80 and -started to study which pin each signal should go to. However I quickly -realized that performing the mod would require soldering around the XV -chip inside the SD-80, which is still a thing that I’m not really -willing to do; and that I could easily test out my theory on XV-5080’s -R-BUS port because the digital audio output pins on XV-5080’s R-BUS port -is pretty much directly connected to the XV chip through an -inverter.

To summerize … I came up with a solution for a problem that I made up -for myself.

Background check on the chip

The seller of the chip claims the chip is an equivalent of the AL1401 -from Alesis, which sounds quite interesting as Alesis is actually the -company behind ADAT (Alesis Digital Audio Tape, as for why it’s a -tape not a optical interface… that’s a story for another time). -Suspicion that this chip is a Chinese clone arose. So I did a bit of -background on the company … [1]

Turns out, of course it is. While its roots can be traced to the US -in the 90s, design team of coolaudio is now located in China -[2]. Better still, it’s a brand -of Music Tribe, which is Uli Behringer’s company. Yes it’s the same -person who founded Behringer which is best known as the legal (/s) clone -audio equipment manufacturer. ~~No wonder why coolaudio’s product -portfolio is all clone chips.~~

Well, the original AL1401 is pretty much impossible to find nowadays, -so I really have no choice don’t I?

Ill-fated commencement

I ordered the V1401 chips before my end-of-year vacation travel. When -I returned from my vacation, I found these in my mail box:

Suspicious packets -

which may look suspicious to law enforcement… but they are actually -just chips. Not the edible kind.

My prior experience with electronics is only limited to reading -schematics and disassembling (and destroying in the process) hundreds of -home appliances. So I guess I have seen hundreds of printed circuit -boards but I haven’t ever made or designed one of my own. I did take a -class during my undergrad that involved programming FPGAs, which did -have a “drawing schematics on a computer” component to it, but that -didn’t have anything to do with PCB design.

Since I do not have any prior experience working with EDA software, I -toyed with an Chinese online EDA toolkit that literally has “easy” in -its name (EasyEDA) and drew a tentative schematic for the supporting -components. Apparently it wasn’t that different from what I used when I -was taking the FPGA class, but at this stage I still haven’t confirmed -many aspects of the characteristics of R-BUS yet. As a result there were -a multitude of issues with this schematic. However it did help me come -up with a list of components (“bill of materials” in more professional -terms) needed for the project. I ordered these together with some -prototyping supplies online, hoping to actually build a prototype once -they have arrived.

The error-riddled -schematic -

I need an audio interface with ADAT inputs because none of the bunch -I already own has one. Since the Scarlett 18i8 3rd gen was on sale for -$360 at the time, I decided to get one.

When I was reviewing the datasheet for the components I ordered -[3], I -found out that I’ve ordered the wrong optical transmitter. The part I -ordered was TOTX1353 which only supports up to 500 kb/s data rate … less -than 1/20 required by an ADAT data stream. However for some stupid -reason that I couldn’t recall, I decided to try prototyping with it -anyway.

I soldered one of the V1401 chips to the SOIC carrier board. As this -time I used plenty of proper, good quality flux as suggested the MacBook -repair guy Louis Rossmann [4], the result didn’t look -nearly as bad as my previous SMD soldering attempts and I was quite -happy with it.

On the following day I started showing mild symptoms of a common -cold. Later that night a fever kicked in. The next day I decided to use -an expired Cornweed [5] test kit on myself and found out Cornweed was -growing inside me (hence the name of this subsection).

I got a week off from my workplace to get rid of the Cornweed. Since -I already felt much better after one day, I started breadboarding. It -was finished pretty quickly. But soon after that I found out there was -more than one thing wrong with the optical transmitter module I chose – -the module doesn’t have a drive circuitry built in and it pretty much -just a bare LED. There is no way in hell that it can be directly driven -from the output of a 74LS04. The LED in the transmitter only barely -lights up when the output is active. At this point I finally realized -that I can’t use this out of spec piece of crap in the final design -anyway, so I placed order for a few transmitters that are more fit for -the job.

- - - - - -

The chip on its -breakout board -

The breadboard -prototype before it was working -

When I was trying to wire in the DB-25 terminal block, I found out -that I don’t have the proper flathead driver for the screws. So I had to -get one of those as well.

Once I really had all the items I need, I started putting things -together. The process was fairly easy but the audio interface didn’t see -the ADAT signal on the first attempt. I double checked all the -breadboard connections and inputs to the chip, which appeared to be all -correct. Feeling tired, I removed the prototype from my desk to work on -it the following day, unplugging all the cables in the process.

To my utter surprise, the thing straight up worked when I plugged it -in on the next day. It turns out that the port on the new transmitter is -very tight and takes quite a bit of force to insert the plug all the way -in.

Working prototype! -

Designing the board

I decided to switch to KiCad soon after I started the actual -prototyping process, probably due to my bias towards free software.

Drawing the schematics wasn’t hard. Although I did have to read the -manuals to find out how buses work in KiCad.

There is no symbol for the V1401 chip in KiCad’s default library, and -no symbol or footprint for the optical transmitter. I had to learn how -to draw these and make them myself. Fortunately the process is pretty -straightforward and the datasheet has everything I need.

I spent some additional time studying the digital / analog audio -output section of XV-5080 to find out the format of digital audio data -coming out of the XV chip. Once that was done I was able finalize the -schematic. I started learning routing in KiCad soon after that. However -that effort was put on hold as soon as I realized I should really -validate the schematic on breadboard first.

Once I got the breadboard version working, I started working on -routing the board again. It started pretty difficult, as certain -crossings couldn’t really be avoided. However once I started making -liberal use of vias the problems got solved pretty quickly. I then -recalled seeing large ground plane on most circuit boards that I’ve laid -my eyes on and found out those can be made in KiCad with “zones”. -However for some (not completely insane, but still pretty stupid) reason -I thought adding too much copper could add to the manufacturing cost, so -I was … quite stingy with the zones. Maybe I should fix it in the next -revision.

Finally I added some personal markings on the board. I decided to try -the svg import feature of KiCad and drew something in Inkscape within a -minute. Once placed on the board it actually looked pretty nice. Yes it -is a Touhou reference, now stop asking why.

- - - - - -

Unfinished -schematic in KiCad -

First attempt at -routing. The board was laid out very differently. -

Board production and final -assembly

The design was now ready and I started looking for PCB manufacturers. -I settled between a few Chinese manufacturing providers for price -considerations. My final manufacturer of choice was JLCPCB, mostly -because they have the best reviews in China. I submitted the files and -waited anxiously for the boards to arrive.

The boards arrived astonishingly fast. In just 5 days it went through -the entire production sequence as well as the Pacific Ocean, and arrived -at my door steps. I test fit all the components, which all fit just -fine. Next was the final assembly which also went pretty smoothly. After -a quick test the board was found to work perfectly. I was actually -shocked that the very first PCB designed by me worked first try. To be -fair the board itself is pretty simple. It was figuring out the R-BUS -protocol that made the project slightly tricky. Actually I’m pretty -surprised to find out that nobody has done the work already given the -service manual of XV-5080 has been floating around on the Internet for -many years now. Anyway, this has been a fantastic starter electronics -project for me and the process has been quite enjoyable.

- - - - - - - - - -

- - Box from JLCPCB - -	- - It’s between my -fingers… - -
- - First two -components installed - -	- - Assembly finished - -

IT’S ALIVE!! -

Full project timeline

2023-09-27: V1401 chip found on ebay.
2023-12-09: V1401 chips bought from ebay seller.
2024-01-10: Schematic attempt with EasyEDA.
2024-01-11: First batch of components ordered.
2024-01-17: V1401 soldered to breadboard adapter.
2024-01-18: Second batch of components ordered.
2024-01-20: Switched to KiCad. Schematic finished except missing -symbol and footprint for optical transmitter.
2024-01-21: Breadboard built. Created symbols and footprint for -optical transmitter in KiCad.
2024-01-22: Started learning PCB layout in KiCad. First attempt to -route the PCB made. Routing halted later that day.
2024-01-26: First working breadboard prototype. Routing resumed and -finished the same day. Learned how to use zones in KiCad. PCB design -revised.
2024-01-27: PCB submitted to JLCPCB for production. 10 boards -ordered.
2024-02-01: PCB arrived. First board assembled and passed -testing.

Full material cost

This includes all orders placed specifically for this project, -including stuff that can be later used for other purposes. Prices listed -before VAT.

- ------ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Item	Qty	Vendor	Price Total
Half-size breadboard	5	Adafruit	25.00
Breadboarding wire bundle	2	Adafruit	9.90
Adafruit Perma-Proto Super Pack	1	Adafruit	34.95
Hook-up Wire Spool Set - 22AWG Solid Core -- 6 x 25 ft	1	Adafruit	15.95
Hakko Professional Quality 20-30 AWG Wire -Strippers	1	Adafruit	17.50
SOIC-20 breakout 3 Pack	2	Adafruit	9.00
Adafruit Parts Pal	1	Adafruit	19.95
TOTX1353(F)	10	DigiKey	92.88
16SEPC100M+TSS	20	DigiKey	11.56
SN74LS04N	25	DigiKey	19.30
CTS 208-4	10	DigiKey	5.76
DB25-SL-25	10	DigiKey	12.60
CFR-25JB-52-1K	100	DigiKey	2.47
CFR25SJT-52-2K2	100	DigiKey	2.47
1N4002B-G	30	DigiKey	4.32
25SEP10M+TSS	20	DigiKey	18.84
C320C104K5R5TA	50	DigiKey	5.05
FCR684208T	10	DigiKey	33.75
V1401	10	ebay (av13)	30.00
JUXINICE DB25 Male to Male Cable 3 feet, -26awg Tinned Copper Wires,Double-Shielded with Foil &Metal Braid, -D-SUB 25 pin Cable RS232 Serial Cable in Black	1	Amazon	12.99
Antrader 2PCS DB25 Breakout Connector -D-sub 25-pin Female Adapter RS232 to Terminal Board Signal Module	1	Amazon	11.99
Focusrite Scarlett 18i8 3rd Gen USB Audio -Interface	1	Sweetwater	359.99
Mako Driver Kit - 64 Precision Bits	1	iFixit	39.95
PCB Production	10	JLCPCB	14.50

Grand Total = $810.67

Potential future work

~~First of all I need to fix the stingy ground plane.~~

V1401’s datasheet isn’t very clear on whether it can generate a -24-bit ADAT stream. Recordings made with the Scarlett 18i8 seem to have -the full 24-bit resolution, but that could be due to interpolation done -by the audio interface or operating system. Testing this requires an -oscilloscope which I currently don’t have.

It is highly feasible to implement an ADAT encoder / decoder in -software on cheap microcontrollers like the rp2040. The ADAT protocol is -documented here and -seems fairly straightforward to implement. This also has the added -benefit of making sure that 24-bit ADAT is really supported. However -this will also more than likely require an oscilloscope for debugging. -I’ll also have to learn rp2040’s PIO programming and theories on PLL -operation, both from scratch.

Exposing the MIDI interface on R-BUS also seems possible. However it -seems that XV-5080 doesn’t make use of the MIDI interface on R-BUS -[6].

~~Maybe I’ll add more Touhou references to the silkscreen, who -knows.~~

I want one! What should I do?

First of all I’d suggest giving the manual -a read to make sure this board really does what you want.

If you have made up your mind to get a board, I have some bad news -for you. Unfortunately right now there’s no straightforward way obtain -this board. Mainly because I have never sold anything online. Also this -board is bound to be a very niche product, and possibly can’t even -recover the development costs if I decided to sell them. Those are the -reasons why I currently have no plans to sell the board.

So right now your options are:

Build the board yourself. The design is fully open source and build -instruction is included in the manual. If you are comfortable with -electronics DIY projects, this is probably your best bet.
Let me know you want one! Right now I still have a few -pre-production boards lying around. As long as you’re willing to cover -the terrible USPS shipping rates I’m willing to assemble a board and -send it your way. Of course you’re welcome to pay a little bit more… but -any excess for now will be treated as donations (a “pay what you think -it’s worth” model) – as I don’t have pricing fixed yet. Also if enough -people have expressed interest in the board I might actually start -selling them…

You’re an idiot and -your design is trash!

First of all, thank you. I am indeed a massive idiot.

If you have suggestions on how this board could be improved, please -consider sending them to me. As a beginner in electronics design I can -definitely use any piece of advice coming from pretty much anyone in -this field. Any constructive suggestion will be greatly appreciated.

Of course other types of contributions will also be appreciated. For -example this board currently lacks any kind of enclosure as I have zero -idea how to create 3D models for real-life object manufacturing. Help in -this space is desperately needed.

Acknowledgment

I’d like to thank Palto for being extremely -supportive towards this project, including putting up with my endless -DMs on Discord.