Casio SA-21

goldenbaby · December 14, 2008, 08:59:00 PM

Bright, pretty robustly functioned keyboard. I love the drum pads, but can't see myself using more than a handful or two of the 100 tones in the bank. I poked around briefly but didn't find anything very reliable or awesome, but there's got to be something kicking around here, at least a pitching bend or some distortion. If I can get some distorted low frequency playability out of these keys, then I'll put on some strap pegs as well, for live usage.

I know Casios are classics, but I've heard very little about the Casio SA-21, though it has similarities to someo f the others SA series.

computer at sea · December 14, 2008, 09:58:49 PM

Try the voltage drop with this guy. There's details over in the SA-1 thread.

Signal:Noise · December 21, 2008, 01:54:50 PM

Voltage drop only works with batteries on this one, I was unable to find a point on teh board that would get the voltage drop to work with a DC adapter. I may have pictures from back when I modded mine, I'll have a look for you at some point.

goldenbaby · December 21, 2008, 09:42:56 PM

That'd be awesome.

Gordonjcp · December 21, 2008, 11:09:16 PM

Quote from: Signal:Noise on December 21, 2008, 01:54:50 PM
Voltage drop only works with batteries on this one, I was unable to find a point on teh board that would get the voltage drop to work with a DC adapter. I may have pictures from back when I modded mine, I'll have a look for you at some point.

One would assume that you'd need to put a resistor in series with the output of the voltage regulator, otherwise the regulator will... regulate ;-)

goldenbaby · December 27, 2008, 06:40:41 AM

Quote from: Signal:Noise on December 21, 2008, 01:54:50 PM
Voltage drop only works with batteries on this one, I was unable to find a point on teh board that would get the voltage drop to work with a DC adapter. I may have pictures from back when I modded mine, I'll have a look for you at some point.

That's cool, I plan to stay batteried. But could you direct me as to the bends you found on this? It's hard finding info on this guy, he's not a very popular SA keyboard it seems.

Tried a 1k pot for the voltage drop, but it didn't work. I don't think I'll be able to obtain a lower value pot, so how would I obtain 100 ohms of resistance by throwing some resistors in parallel. I don't know how to calculate that.

goldenbaby · January 18, 2009, 11:04:16 PM

I'm still wondering about this keyboard, as none of the other SA series info I read -- regarding other models -- is useful for this keyboard. And I have not found a great pitch bend or distortion yet. The voltage drop should be easy, just not sure what kind of resistor to get: supposedly pretty low value, but I'd hate to buy another pack of another value, and it be useless. 200 Ohm, if I remember right. It's hard for me to even find that value of pot, so how do I calculate what statics I need to put in parallel to achieve such minute resistance?

PolyPhuckin · January 19, 2009, 08:46:02 PM

I have an SA-21 waiting for me to open her up, quite interested to see what i can find.

What i generally do for power crashes is set up a potential divider, i find its a lot more stable and you can set a lower voltage limit rather than taking it all the way to zero. heres a good page on setting one up http://www.beavisaudio.com/Projects/DBS/

Granted, that page is telling you how to set one up for FX pedals, but its easy to apply it here as well.

computer at sea · January 21, 2009, 12:44:08 AM

Thanks for the great link!

PolyPhuckin · January 21, 2009, 07:42:30 PM

Yeah amn, the guy who runs that site has some amazing projects and ideas on there.

goldenbaby · January 21, 2009, 10:54:33 PM

K, maybe I'll give that a shot. What values would you recommend using to better suit a small Casio like the SA-21?

PolyPhuckin · January 23, 2009, 11:32:30 PM

Off the top of my head, i cant remember what voltage the SA-21 runs on, 6 i think

generally what i've found with power crashes on the lower SA's is that you get the best crashes when the voltage drops by only a few volts, say 3. You get a good range then and lots of play.

+6V__
|
|
VR 1KΩ
|
-------------------∧
|    |
1KΩ Take the power for the circuit from between these two points
|    |
|          |
0V------------------------v

(does that make sense? $:-\$ )

This set up will drop it to 3 volts, if you find that this is too much, exchange the 1K fixed resistor with a 2.2K. This'll bring it up to about 4.12V

Play around with combinations until you get something that works.

goldenbaby · February 05, 2009, 02:43:49 AM

Dude, I got those parts on hand and gonna try it tonight. The SA-21 is actually 7.5V, which means your diagram might give me even more control. Either way, I'm amazed I can get such control out of 2 1k ohm components.

PolyPhuckin · February 05, 2009, 07:39:57 PM

Haha. thats true, i dont know why i thought it was 6v

But if you replace the fixed resistor with a 4K7 resistor it'll only drop to about 6.1v which should be fine. If you left it as it was then you'd be dropping to about 3.75v, which is a bit too much of a drop.

goldenbaby · February 06, 2009, 10:40:13 PM

I tried the 1k pot w/ 1k fixed and I still didn't have enough control to tune into CRASH mode.

If by 4k7, you mean 4.7k pot, then I'm gonna try a 5kohm fixed resister to see if it works.

Apparently 470 ohms crashes the machine nicely, but I can't find that low of a value locally, unless i want to pay $10. It's bunk.