Build: Midibox FM

[playthatbeat]

So, i mentioned previously about the OTHER 'Sammich' midibox kit available, the SAMMICH FM, and how it was inbetween batches.. I wanted a MBFM,
so i got the bits and did it..

I needed:

* CORE module kit and pic
* Digital Input board (DIN module)
* OPL3 board & various parts
* OPL chipset
* Box/case (cheapest i could find!!)
* LCD screen
* 10 buttons
* 1 encoder
* 5 pin DIN sockets (for midi)
* Panel mount 1/4" Jacks (for audio out)
* usual nuts & bolts and wire and crap
* PSU that did +/- 12V

This page has the basics, I used this core and the OPL3 board from the same guy (smashtv) http://www.ucapps.de/mbhp_opl3.html

Got my OPL3 YMF262 and pairs of YAC512 on ebay, a nice cheap 20 x 4 display and went for it..

You can get a kit for the CORE of coarse, so that was the easiest bit.. Getting the bits for the OPL board was annoying, as certain things weren't available, like the 2.7pf caps - all i could get of them was a 'bullet belt' of VERY small SMD, so i used them at the back of the board, and used 2.2pf for the other 2 places near the middle.

Got them done anyhoo, and since i had a 1/2 broken DINX-4 from my MBAY build, i threw in some buttons as well.. the ESC, select 1-8, and i connected up the main encoder as i had a scrap BOURNES encoder in the crap box. i also connected up a button for CFG. I had planned to use the entire thing by remote (midi) using the Midibox FM CTRLR SysEx Editor application, but the thought of buttons pleased me.

I rigged a piece of proto board with micro switches, and used bolts and extenders to hold it behind the case, drilling holes to let the buttons poke through. really simple to do once i'd made the board up and layed it over graph paper to make a pattern for the holes. This pattern is then taped to the surface of the box, and a hot soldering iron is used to burn pilot marks thru' the paper, then these holes are made proper with a drill.

I wanted a screen, and hooking that up was of COARSE the biggest pain in the ring, as always. BUT, done now, and looking fine. These LCDs are the 2nd most expensive item in the build, being an odd shape. You can get non-backlit ones on fleabay for $6, but as you can see, i fell for a nice blue/reverse one that cost me nearly triple the price of a non-backlit

I had a problem with Idle noise - this was cured by taking the (-) ground from the audio out sockets and connecting them directly to the PSU ground, instead of the point on the CORE board as per the build instructions.

I used a TRACO txl035-1212d PSU to get the +12 and -12 v DC power: the biggest expense in the whole project, but after fuc*ing about on previous builds, this had to be done. I know you THINK you need +5v as well, but You don't. Just power the OPL board with the +/- 12v & gnd, and the CORE board from the +12 and gnd. Turn down the adjust on the PSU to minimum, which is about 11V to keep the regulator on the CORE from getting too hot.

The build was fine really.. Pay heed to the way you interconnect things, and You will be fine. Follow the build instructions to the letter, and if You have noisy outputs, run the shield on the audio out jack(s) to the gnd of the PSU like i did..

If you are going for a pure remote version, you only need the CTLR app and the 2 boards and PSU.. You don't NEED a screen or buttons..

How does it sound? its a 4op FM synth.. very much like a Yamaha DX100 or 27 or 21, but this CLEANER sounding, multitimbral, has some new quirks and is a little glitchy.. in short, a tradeoff that wins.. See the next post for a sample of it in Detroit mode

NEWFLASHNESS: There is another batch of Sammich FM being done, so if you want a full kit, no fuc*ing about, then contact 'wilba' - You will find him at the midibox.org forum, and there are plenty of details on him in the various Wiki pages for SammichSid And SammichFM at midibox.org.. This will bypass 100% of the drama in building and gathering and so on.. he EVEN HAS THE OPL CHIPSETS.. I would have totally gone this route had the SammichFM been available when i got the itch..

[playthatbeat]

First play with the MBFM.. just a stabby chord while fiddling about, the usual..

[playthatbeat]

now the gory details in picture form..

you can see all the important bits here.. i mounted the CORE and OPL boards on the metal plate that forms the bottom of my case.. the rest of it was used to hang the screen and controls and encoder boards on, using mini bolts and nuts and such..

Interconnections were with ribbon cable from SmashTV and plugs/pin SIL risers where i could..

You can also see the tiny OPL chipset (SMD) soldered onto the underside of the OPL board.. there is no avoiding this - even the Sammich FM kit needs You to get in there and do it.. It's EASY. seriously. just tin 1 pad and hold the chip in place, then tap the pad with the iron, it will anchor.. you can re-heat and shift it if you aren't sure, but just go ahead and dab all the pads with solder with the pins over them and make it happen. you will get the idea after 1 or 2 pins. just take it easy, and be quick & sure of yourself. If you are not sure, then go ahead and tin up all the pads - then cut some strips of masking tape, and tape your chip over the pads - easy to do since there are only pins on 2 sides, you can run the tape across the chip to hold it in place, then tap/feed the pads to bond the legs to them. you CAN bend these little legs you know, but only a couple of times..

You can also see how i got it all into the case.. that shot is from behind of coarse, with the unit on it's back. Yes, the case is meant to be used the other way up, but it was alot easier to cut a window for the screen in the plastic then in the metal base! Yes, thats the BANKSTICK off to the right, taped to a piece of foam.. The power socket is an old 4-pin CB microphone plug and socket, i used 3 pins to do -12v +12v and GND..