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Yamaha DX7 Technical Analysis

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Re: Yamaha DX7 Technical Analysis

#91

Post by HeyLaughingBoy »

mikewarot wrote: post #82

The numerically controlled oscillator (NCO) aka Direct Digital Synthesizer (DDS) at the heart of this is one of the most elegant things I've encountered. I once used an NCO to adjust for belt speed variation in a machine that applied hot glue to corrugated boxes in a production environment. The CPU I had at the time was constrained to 512 Bytes of EEPROM to store the program in, and it (the NCO) really helped fit tha…

I have to ask. Was the MCU by chance an MC68HC705K1?

Asking for a friend :-)

Re: Yamaha DX7 Technical Analysis

#92

Post by QuadrupleA »

I've been restoring a closely related DX11 recently - one interesting tidbit of over-engineering, the keyboard matrix for the tact switches on the front panel (not just the musical keys) has a diode for every switch, to apparently allow "chords" of 3 or more programming buttons to be held and scanned at once. Can't see why it's needed during programming of the patches, but I might be missing something. Maybe someone had a kickback deal with the diode vendor to ship an extra 40 of them per unit :).

Re: Yamaha DX7 Technical Analysis

#93

Post by jlarcombe »

z5h wrote: post #71
tgv wrote: post #4

Plogue, a Canadian software company, have recently released a (software) emulation of the DX-7 in excruciating detail. Here you can see part of the trouble they went through: https://www.youtube.com/watch?v=XJ97iXQrqzw . Suffice to say that they used a logic analyzer to discover gritty details that no other analysis of the DX-7 I know has ever paid attention of.

I like to think I’m a synth nerd in the know, and certainly chat a lot and read synth forums. But Plogue have flown under my radar. This looks like great stuff at a good price. Do you own any of their soft synths?

they're super great, their software is ace. we used to work with them at my old company and they're lovely people too!

Re: Yamaha DX7 Technical Analysis

#94

Post by RusticCajun »

jacquesm wrote: post #5
danbmil99 wrote: post #2

Awesome -- the DX7 had a huge musical impact.

I repair them to keep them in play, impossible to get some of the parts so I tend to use one that is too far gone to repair a number (usually three or so) of others and then I still end up with some more spares that might come in handy later. They are incredibly durable, one that I got had been in a fire but it still worked, even though more than half of the keyboard had been burned off. The mainboard went on to repa…

Do you work at all with KX88's? I've got one laying around. Got it for the college dorm. Wasn't as good as my acoustic, but it kept my fingers working. How can I contact you directly?

Re: Yamaha DX7 Technical Analysis

#95

Post by jacquesm »

QuadrupleA wrote: post #92

I've been restoring a closely related DX11 recently - one interesting tidbit of over-engineering, the keyboard matrix for the tact switches on the front panel (not just the musical keys) has a diode for every switch, to apparently allow "chords" of 3 or more programming buttons to be held and scanned at once. Can't see why it's needed during programming of the patches, but I might be missing something. Maybe someone…

I think without that diode there would be ambiguity about which switch is pressed, it keeps the rows and columns in the matrix separate so no current can flow back to other rows/colums when one key is pressed.

Re: Yamaha DX7 Technical Analysis

#96

Post by jacquesm »

RusticCajun wrote: post #94
jacquesm wrote: post #5

Earlier quoted context omitted.

I repair them to keep them in play, impossible to get some of the parts so I tend to use one that is too far gone to repair a number (usually three or so) of others and then I still end up with some more spares that might come in handy later. They are incredibly durable, one that I got had been in a fire but it still worked, even though more than half of the keyboard had been burned off. The mainboard went on to repa…

Do you work at all with KX88's? I've got one laying around. Got it for the college dorm. Wasn't as good as my acoustic, but it kept my fingers working. How can I contact you directly?

Haven't seen one in the wild yet, jacques@modularcompany.com is my email.

Re: Yamaha DX7 Technical Analysis

#97

Post by tomcam »

noizejoy wrote: post #14
tgv wrote: post #4

Plogue, a Canadian software company, have recently released a (software) emulation of the DX-7 in excruciating detail. Here you can see part of the trouble they went through: https://www.youtube.com/watch?v=XJ97iXQrqzw . Suffice to say that they used a logic analyzer to discover gritty details that no other analysis of the DX-7 I know has ever paid attention of.

Another venerable DX7 software emulation worth mentioning is the free and open source Dexed[0], which also doubles as a patch librarian for a real DX7. [0] https://asb2m10.github.io/dexed/

Wow, thank you

Re: Yamaha DX7 Technical Analysis

#98

Post by QuadrupleA »

jacquesm wrote: post #95
QuadrupleA wrote: post #92

I've been restoring a closely related DX11 recently - one interesting tidbit of over-engineering, the keyboard matrix for the tact switches on the front panel (not just the musical keys) has a diode for every switch, to apparently allow "chords" of 3 or more programming buttons to be held and scanned at once. Can't see why it's needed during programming of the patches, but I might be missing something. Maybe someone…

I think without that diode there would be ambiguity about which switch is pressed, it keeps the rows and columns in the matrix separate so no current can flow back to other rows/colums when one key is pressed.

You can definitely do 2 simultaneous keys unambiguously without diodes; 3 keys is where you sometimes get "phantom keys" by bridging other rows / columns to each other. Depends on the matrix layout though, if you have say an 8 x 8 matrix for 64 keys and each pressed key is on the same column or row, you can read 8 simultaneously without any problems.

Most PC keyboards leverage this so they can skip diodes, and just route the matrix so that common simultaneous combinations (modifier keys, WASD for games etc.) don't interfere with each other.

Re: Yamaha DX7 Technical Analysis

#99

Post by jacquesm »

QuadrupleA wrote: post #98
jacquesm wrote: post #95

Earlier quoted context omitted.

I think without that diode there would be ambiguity about which switch is pressed, it keeps the rows and columns in the matrix separate so no current can flow back to other rows/colums when one key is pressed.

You can definitely do 2 simultaneous keys unambiguously without diodes; 3 keys is where you sometimes get "phantom keys" by bridging other rows / columns to each other. Depends on the matrix layout though, if you have say an 8 x 8 matrix for 64 keys and each pressed key is on the same column or row, you can read 8 simultaneously without any problems. Most PC keyboards leverage this so they can skip diodes, and just r…

Hm. I don't know about that, I thought that the problem already existed for 2 diagonally opposing sets of buttons: you can't tell the difference between the two.

so:

       | | | | | | 
    ---+-+-+-+-+-+-----
       | | | | | | 
    ---+-+-*-+-+-+-----        
       | | | | | | 
    ---+-+-+-*-+-+-----
       | | | | | |
and

       | | | | | | 
    ---+-+-+-+-+-+-----
       | | | | | | 
    ---+-+-+-*-+-+-----        
       | | | | | | 
    ---+-+-*-+-+-+-----
       | | | | | |
Would look identical to the CPU without diodes.

Re: Yamaha DX7 Technical Analysis

#100

Post by mikewarot »

HeyLaughingBoy wrote: post #91
mikewarot wrote: post #82

The numerically controlled oscillator (NCO) aka Direct Digital Synthesizer (DDS) at the heart of this is one of the most elegant things I've encountered. I once used an NCO to adjust for belt speed variation in a machine that applied hot glue to corrugated boxes in a production environment. The CPU I had at the time was constrained to 512 Bytes of EEPROM to store the program in, and it (the NCO) really helped fit tha…

I have to ask. Was the MCU by chance an MC68HC705K1? Asking for a friend :-)

It was a 68HC11, I forget the specific model number, they had a few development boards for $68.11 in the local college bookstore, so that's how I prototyped it. ;-)
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