Casio DG-20 digital guitar

[Circuitbenders]

I'd be a bit wary of messing with those big square chips  but the one at the bottom middle on 'The main board, track side' with one of the main chips to the right has got bendability (and i'm trade marking that word)  written all over it.

[gmeredith]

You mean "main board, component side" instead?

Here are the 3 main board component side chips:

[gmeredith]

More pics:

The bottom, secondary board:

[gmeredith]

The secondary board main chip:

[gmeredith]

The speaker (5"), and the output socket board with MIDI out. I suspect that this whole module contains the speaker amplifier components also, as there is a lot of components in it:

[gmeredith]

This synth appears to be very modular. There are quite a few discrete circuit boards in it. I really like what seems to be a completely separate amplifier module. That will lend itself well to inserting effects circuits, separate drums output etc. As you can see from the inside shots, there is a HUGE amount of space in there to work with. The front and sides of the guitar also are vacant lots waiting for controls. This thing ain't no tiny SK-1 or something!!

I'm in the process of ordering the DG-20 Service manual from these guys:

http://www.wdgreenhill.com/

I'll let you know what it reveals when I get it.

Cheers, Graham

[kb]

Signal:Noise: 
regarding the filterchip, I'm pretty sure that the MT600 was the only MT that had that chip.  The 600 was a bit of an odd duck and, I think, the very last 'Casiotone.'  So you probably didn't miss out when you sold your MT55.



Graham - thanks for posting these - at long last the secret innards of the DG20 are known!

my guesses at the hardware:

-    first of all, no obvious filterchip 

-    the D931's gotta be the music LSI.  My HT uses the D935 and has a SMD form factor.  Tablehooters (thanks for link to archive!) says  the D931 is the main voice chip for the MT800 and the wonderful MT400V/CT410V, so whatever bends apply to those might apply to your DG?  And by the way, what's going on with that 'tunnel' along side the D931???

-   I'd venture that the M6294-06 is the percussion chip, because my HT has M6294-03,04 chips for drums. 

-   The D78C10 is in my HT, so that's shared.  Probably the main CPU?

-   The D23C256 is also in my HT.  Program ROM, likely.

-   The MB64HB119's certainly turn up on a Google search, but only as a listing from distributors.  Not sure what they are, perhaps RAM?

Now we eagerly wait for you to bend the DG!

[gmeredith]

Hi KB,

The "tunnel" next to the D931 chip is just a resistor network bank. It's glossy and so gives the appearance of being cylindrical, but it's flat and vertically mounted.

So it's sounding very much like it is the sound engine for some MT/HT casio keyboard, modified. The sounds are definitely not sampled PCM, they're synth sounds (except for the drums, they're the familiar PCM sounds, with the snare drum that sounds like a large plastic bucket being hit by an enormous stick of salami), which is why they sound very clean, compared to the PCM sounds released after this era. Interesting in that the Tablehooters website MT800 page mentions that the MT800 was one of the only casio's to run off 9V DC instead of 7.5V DC. My DG-20 specifies 9V DC supply, so that could be another bit of evidence.

I'm going to buy the service manual from www.wdgreenhill.com which will reveal much about the processor and sound circuits. This thing is so well spaced and uncluttered on its board that there is ample room for mods.

Cheers, graham

[gmeredith]

Just got the DG20 service manual, wooooot!!! It has revealed a wealth of info for bending. So far, I've installed large capacity D-cell nicads in it, and a charging socket, working well. Now I can prance for hours!

I've tried disabling the auto power off feature, but to no avail (see my other topic on this subject). I may come back to it and try again later.

The one thing that the schematics reveal is that the DG20 has very modular, discrete sections, very good for bending. It has an LFO section, an analog chorus section with a BBD chip and it's own VCO, and a flanger section (an additional part of the chorus), and a discrete distortion ciircuit!! It also has a LP filter circuit, although it does not appear to be CV controlled or have resonance, just a basic fixed filter, however it does have several selectable R-C networks in it to give different cutoff frequencies. This would lend itself to some analog pot controls very easily.

I'll scan them when I get the chance and show you all!

**update**

I've just uploaded the DG10/DG20 service manual and schematics here:

http://www.jz-server.de/forum/e107_plugins/forum/forum_viewtopic.php?1134


Cheers, Graham

[MarsHottentot]

YOU'RE POST HAS FORCED MY HAND

I'm drooling at the prospect of hearing what you're going to do!
I've got a DG-1, but my bending skills are so bad, I'd be on here basically having all of you tell me exactly what to do!
........................................... ...............................................
No takers?  no?...no?

Anyway, I'm very excited to hear what insane stuff you come up with.
Great board!  Hope you guys don't mind an enthusiast hanging out and cheerleading!

[gmeredith]

I'm storing up all my bends for when I take holidays, so I haven't done any on it yet, but I've been cataloging circuits and all the bend points on it, so that when I get time, I'll do them all. Probably one of the most important bends I want to do is the 1 octave drop mod. I can't believe that Casio didn't provide some bass sounds on this thing. The octave drop will enable me to get this, Kerry Bradley has been helping me design the clock circuit that will do this. Another mod I want to do is add a filter circuit with resonance, which I've been drawing up the schematics for. I'll post them when I finish them.

The DG-1 should be pretty much the same in essence as the DG20, so the same mods should apply to it also.

Cheers, Graham

[MarsHottentot]

SLOBBER!
That's hot!

RE: Casio and missed opportunities.
I don't know how old you are, but as I remember it, when Casio hit it big as the maker of THE SYNTH that every family owned, wild sound options weren't 'cool'.  Parents wanted a piano alternative, not a box that went 'bzzzzzeeeeoOWOWOWOWO' y'dig?.  In fact, there was a real backlash to the whole 'synth sound' generated by analogs. They were seen as confusing and archaic. 'Beep Boop' and 'Devo' were playground insults.  I got called 'Devo' a few times myself.  No, sound emulation was what John Q. Consumer was looking for.

Basically, all of the things that you can dig up on your garden variety synth that would turn them into a modular monster was probably avoided on purpose!

Any other theories?

[gmeredith]

Yeah, I remember those days, in 1985 my keyboard player in my band borrowed this "amazing keyboard" from the music shop he worked at - he rocks in with this Ensoniq Mirage under his arm. **Wow, real instrument sounds!!**
From then on, DX7 electric piano sounds were dead. Everyone wanted real sounds, no synthesis crap. TR909's landed on the market but couldn't sell. Noooooo, it HAD to be a Linn Drum or SCI Drumtrax. My God, even TR707's were considered "real" drum sounds, with their 0.5 second crash and ride cymbals.

I picked up my BLUE SH101 with matching handgrip in the late '80s for $120 in a 2nd hand shop, as well as a Yamaha CS01 and SHS-10 keytar for less than that again together! I got a TB303 bassline for $100, I snapped up 2 TX81Z's for a couple of hundred each at the time, a Casio CZ101 for about $100 and a Casio SK-8 for about $30. None of those keyboards were more than about 6 years old when I bought them. So the'80s were kind to me, look at all of them now (maybe not the TX's) and the prices they're fetching! And the embarrassing old "analog" TR909 has had the last laugh of them all!!

I'm a real sound tweaker, I rarely end up using the preset sounds on a keyboard, so I'm grateful to still have "synths" that you can tweak. I do have a Casio FZ-1 sampler, which is more a synth than it is a sampler because it has an amazing amount of parameters to apply to samples, and a DCF with wicked resonance!

The 80's. What a crazy time!

Cheers, Graham

[Circuitbenders]

ahhhh, the Casio FZ-1 resonance parameter, the stuff that lo-fi dreams are made of 

[MarsHottentot]

I didn't get the synth bug until '94 (although I was feverish for the DG-20 when that came outin the 80's, I'd wail on it in the 'Service Merchandise' store until a clerk would come and tell me to stop), but by then they started to catch back on, prices rose and I was a broken down post-grunge wastoid.  I scored a Roland GR 700 and a half cashed Crumar Trilogy.  The Roland was actually awesome, I kept it for years before selling it in financial desperation.  The Crumar was pretty horrible, but it got me interested.  Circuit bending really sold me, though.  I got a patchbay SK-1 and my brain lit on fire!  These are new sounds!!