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The other day I decided to take our Yamaha AN1x apart to gaze upon it "in the buff" and scope out the naughty bits. This keyboard is a synthesizer, of the "analog modeling" class. That is, it is a DSP implementation of an analog synthesizer, so there are things like VCOs, VCFs, VCAs, function generators, etc. in there but all are done numerically rather than with analog circuitry ala MOOG. It can do a pretty nice pipe organ, and the EP patches aren't too bad, but as you might expect it isn't nearly sophisticated enough to make realistic piano sounds. Polyphony is a low 10 I believe - this is more of a lead instrument than anything else. I don't think Yamaha made too many of these, ours was a Sam Ash floor demo so we got it pretty cheap a long time ago.

My main interest in disassembling it was to examine the X-Z controller on the left hand side of the instrument. Being X-Z, it senses where your finger is on it in the X (side to side) direction and how hard your finger is pressing in the Z (downward) direction. If you've ever played with an AN1x for any length of time you know how lively and responsive this controller is - I've never encountered anything quite as musical on any other keyboard. Patches generally use the X axis of it to set the cutoff frequency of the low pass filter. When the order of the filter is high, even slight changes to the cutoff frequency can make a dramatic change in the overall sound. It's loads of fun to play with. OK, on to the disassembly.


Here is the AN1x disassembled. You have to remove every freaking screw on the bottom to access the insides. The bottom then lifts off and everything is securely mounted to the top plastic section. I don't know about you, but in the past I've been burned by removing too many screws, so it always gives me a queasy feeling when I end up having to remove them all. Anyway, you can see the massive PWBs for the keyboard assembly and for all the I/O, along with a central main board, and a tiny board for the X-Z controller located above the pitch & mod wheels (shown here on the right since the unit is flipped over).


A view of the main processor board. That's a lithium backup battery at the upper left, with 2Mb SRAM below it and a general purpose H8 processor to the right of it. A daughter card is plugged into the center of the main board.


A view of the daughter board unplugged and sitting on top of the main processor board. Same exact two chip set on both, must be some kind of DSP, perhaps with associated ROM. That's some DRAM and I believe the D/A converter in between.


A view to the right side of the guts. Here you can see the pitch and mod wheels, which BTW are only supported by their respective pot shafts & pot bearings (not the most rugged arrangement). Above them is the X-Z touch controller. The touch pad mounts under the tan PWB, though I had removed it by the time I took this picture, so the PWB screws are shown removed here. The pad plugs into that white connector near the top of the PWB. That's a dual op-amp (4558) on the PWB, not much else, though the trimmers are something of a surprise - EEs always try to design those out if they can - they are expensive, and literally no one wants the added manufacturing step of adjusting them on the assembly line.


The X-Z touch pad removed and sitting on my bench. To remove it you have to remove the 4 screws holding in the tan PWB, then slide the plastic sleeve on the electrical connector forward so that it releases the printed mylar cable.


And here is where the crying starts. I really thought the X-Z touch pad was capacitive in nature, like those laptop mouse pad thingies. When I first opened up the AN1x I was somewhat shocked to find almost no circuitry supporting the touch pad (see previous photo) but when I peeled back the top protective plastic on the pad, the awful sickening truth was laid bare. My beloved touch pad, with which I'd had so much fun, so many fond memories, turned out to be a cheap contrivance made of carbon deposited conductive plastic! I had been taken in by a simple resistive sandwich! There are some things in life one is better off just not knowing, and for me this was one of them. I went and took a shower but couldn't wash away the tawdry, used feeling I had.

Afterward, listless, I played with the touch pad for a while on the bench. Of the five connectors, two are for bulk pressure (~20 Ohms pressed hard, infinite Ohms untouched), and the other three behave like a ~9k Ohm potentiometer - but only when there is a finger pressing on the touch pad. Plugged into the AN1x, I saw a 15ms period inverse 5V sawtooth when the pad wasn't being touched, and almost full 0-5V control range for both axes when touched / pressed (minus a diode drop perhaps).

Here are some of the parts on the main board:

HD6413002FP16 - H8/3002 Microprocessor, Hitachi
HM6281288LFP-8 - 1 Mb (128K x 8 bits) SRAM, Hitachi
LC321664AJ-80 - 1 Mb (65536 words x 16 bits) DRAM, Sanyo
HD62098 - Stereo D/A? Hitachi
Yamaha XS467 - house numbered, uP ROM?
Yamaha YSS236-F - house numbered, DSP?
Yamaha XT113B0 - house numbered, DSP ROM?

I buttoned it back up and checked the keys, wheels, and touch pad - all worked as before, but much of the magic was gone.

LOL!!

Thank you for the fascinating photos and entertaining thread. I obviously need to start hanging out in the digital forum more often.

p.s. I would *never* have enough courage to take apart a functioning electronic device, so I am happy to get the chance to satisfy my curiosity with somebody else taking all the risks!

I either broke - or for one reason or another never put back together (same thing really) - everything I took apart as a kid, and I took everything apart. It got so my family started hiding their personal electronics items.

My fix to break ratio is much higher now, though even if I live to 100 I'm not sure if I'll be able to make up for those early destructive years.

Mamas, don't let your babies grow up to be engineers.

Im thinking of taking my px-130 apart (Yup, electrical engineer) to find a way to allow a 2.1 speaker set to be used in conjunction with the onboard speakers. The onboards have alot of mids that Ive heard many 2.1 systems lack, so I think they would work well together.

Anyone have a good idea of how to do this without having to resolder the entire input area?

I did this a couple of years ago to the Yamaha my wife plays at a small local church. I was using the headphone out jack as a line-out to the PA, but it had some kind of weird, complex auto switch that caused the output to die every once in a while.

I removed the bottom and located the input to the stereo amp inside, and wired a new 1/4" TRS jack to it. That way the volume on the DP controls volume to the PA, and the internal amp is never defeated (it is used as a monitor). Works like a champ.

I did this for my Kawai CP136.
This has two headphone outputs and both disable the speakers when the headphone is plugged in.

The advantage of the headphone output over the line-out is: This is high level audio and compatible with HiFi equipment, while the line-outs are low level outputs. These are made for a PA but the level is too low for ordinary HIFI equipment inputs. Then, of course the plug is easily accessible at the front...

The plugs had an extra contact and this switched a relais. Both contacts where connected in serie and so all I had to do was to short one of the contacts.

I have now one Headphone output that doesnt disable the peakers and I connect my MP3 recorder to this....

Why didnt the Kawai engineers have this idea ;-)

So you just wired a new jack to where the internal speakers connected to the board?



When you say the plugs had an extra contact that you shorted, what exactly do you mean? Do you mean one of the TRS leads as shown below?? Or were your headphone inputs not standard TRS connectors?

There was a nonstandard contact. This had no connection to the audio section.
It switched a voltage that disabled the speakers amplifier.

It was the same with my Yamaha CVP96. I think most pianos that hve two headphone outputs do it this way, otherwise more contacts would be needed and that is more expensive.

So far I know the PX130 recognizes the insertion of a headphone plug and switches the eq automatically. This might be a complication, but I learned fron the german edition of Mikey Mouse and from Daniel Düsentrieb (Gyro Gearloose) : "Dem Ingenör ist nichts zu schwör" (nothing is too difficult for an engineer) ;-)

Peter

Well then, this is good news as the px130 does have the 2 headphone inputs. Ill have to take a look at the jacks and see if it has the extra lead on it. But what do you short the contact to??

Im a very new engineer, so things are still a little difficult!

Now both contact switches where in series.
So if nothing is plugged both contacts are closed, a current flows through them. When a plug is plugged in then one contact opens and the current is interrupted and that disabled the power amplifier. So all I needed was a small drop of soldering tin and I shorted one contact, so that it is always in the "closed" state.

Edit: Probably this was type "C". I did not care much about types unused contacts I could see from the PCB traces which of them where of interest for me and which not...

[img]http://wapedia.mobi/thumb/a4a614775/en/fixed/240/240/Phone_jack_symbols.png?format=jpg[/img]

That said, it is probably not exactly the same for the PX130. You have to look to the actual connections and figure out what they do.

Peter

You are right low-cost 2.1 systems use very small left and right channel speakers that really don't go down very low so even some of the mid-bass has to go through the sub-woofer.

I would think that the best place to tap the audio would be at the headphone jack. This is likely a switched 1/4" TRS jack. If Casio used the now standard "Cliff" style jack the un-switched stereo signal is on three pins along one side of the jack. Drill a hole and install either another 1/4" TRS or to be more like others DPs two 1/4" TS jacks and wire them to the above three pins.

If the headphone signal is to "hot" to serve as a good line out wire up a voltage divider using some 5K to 20K resistors. Your 2.1 system likely has maybe a 20K input impedance the headphone jack is designed to drive 30 ohm headphones. So I'd not be surprised of you need to "pad down" the signal. The divider will add some protection from a short as it will have one resistor in series with your new jack.

Wait, what good would adding 2 more jacks wired to the 2 existing jacks do? Are you saying there are actual physical switches in the onboard jacks and the new jacks should not have the switches?

Also, if the jack is designed to drive a low impedance headphone, wouldnt the signal be too low, not too hot, for a high impedance load??

To the OP: So sorry for hijacking your thread. I hope you dont mind as this is valuable info here and in the spirit of the thread!!

EDIT:

I think I understand the switch part now. I see in this picture a pin that would contact the T pin when no plug is inserted, but when the plug goes in the connection is open. So if this connection is shorted that would fool the system into letting both the internal and external speakers be active right?? Is there any danger of messing anything up by doing this? Id hate to fry something....

No, not speaker level, though some headphone outputs are resistively limited speaker levels.

The guts of the Yamaha were fairly modular, so it was easy to see where the internal line-level went from the sound generation board to the volume control to the amp. Post volume control is where I tapped in, post some buffering IIRC.

The Yamaha had some kind of complex sensing mechanism for the headphone jack. Not a physical switch like you might expect, but perhaps a current sensor going the processor (I only looked at it long enough to determine that tapping into that wouldn't work). They might be doing it that way so that they can defeat any speaker EQ when headphones are plugged in.

BTW, headphone level is very close to line level. You can drive most headphones to comfortable levels with garden-variety op-amps.

Description of switch TRS jack types

See Figure D and corresponding description.

Typically the signal that goes to the internal speakers has that jack/switch wired in series. Some jack switches are more complex and ground the contact rather then just let it "float". The newest devices might be completely controlled by microprocessor. But an old piano likely just uses a simple switch.

But you don't need to care, you want an always-on audio signal. I only pointed out switching jack you you know to tap into the unswitched side of the jack.