Casio SA-1 & PT20

[andy_wheels]

thanks for the sa-5 link. i'll be impressed to see something i've yet to find though. think i've now spent far too long fiddling with the insides of the sa's i have... hhehehehe. 

my voltage drop attempt didnt involve a pot. i cut the wire on the board, which should result in the keyboard showing no life, and nothing happened. the synth still worked fine! so things are a little different on the sa-5 than the sa-1.

[sn7ke]

O_o you cut the power-wire and it still works??!!!
=_=?!! sure you cut the right wire then?

lol. Well...anyway! I got an SA-5 too. Do you mind tell me a bit about the mods you did so far? Maybe it can help me when i start bending the SA-5 this week!

[Block]

I got the voltage drop working with a 470 ohm pod, i also tried it wirh a 1k pot (works)
however with both i can only turn the knob a few millimiter before the voltage already is too low.

Hi sn7ke

Using a multimeter and a potentiometer i've worked out that i need about 80-200ohms hooked into the power supply to give a reliable voltage crash on my SA-20.

This is how to turn any 0-whatever pot into an A-B pot (in this case 80-200ohm)
the mini-circuit consists of  2 pre set resisters and a pot as shown below

----------Resister A----Pot------------------
    \                                    /
     \-------Resister B---------/

Resister B should be your top ohmage so 200ohm.
Use the formula A = RB/B-R to get the value of the other resister. (this assumes that the pot goes down to 0ohm)

for me R=80,  B=200 so
A = 16000/120 = 133 ohms

now we have an idea of the resister's values, check the top resistance. P is the pot value, 100k in this case.
Top R = B(A+P)/(A+B+P) = 200(110+100000)/(110+200+100000)=199ohms

so solder some resisters together and we have an 80ohm-200ohm pot!

I generally use preset pots for A & B so that i can tweak, but this is how you get the starting values.

BTW Use a logarithmic pot with this technique to get a linear scale, linear pots creates a inverse log scaling effect for those who are interested

[masyst]

Have somebody a picture of how they done the voltage drop on a SA-65??

[Evoke.T.Macabre]

Hi sn7ke

Using a multimeter and a potentiometer i've worked out that i need about 80-200ohms hooked into the power supply to give a reliable voltage crash on my SA-20.

This is how to turn any 0-whatever pot into an A-B pot (in this case 80-200ohm)
the mini-circuit consists of  2 pre set resisters and a pot as shown below

----------Resister A----Pot------------------
    \                                    /
     \-------Resister B---------/

Resister B should be your top ohmage so 200ohm.
Use the formula A = RB/B-R to get the value of the other resister. (this assumes that the pot goes down to 0ohm)

for me R=80,  B=200 so
A = 16000/120 = 133 ohms

now we have an idea of the resister's values, check the top resistance. P is the pot value, 100k in this case.
Top R = B(A+P)/(A+B+P) = 200(110+100000)/(110+200+100000)=199ohms

so solder some resisters together and we have an 80ohm-200ohm pot!

I generally use preset pots for A & B so that i can tweak, but this is how you get the starting values.

BTW Use a logarithmic pot with this technique to get a linear scale, linear pots creates a inverse log scaling effect for those who are interested

good thinking.  and good description of applying.  thanks-

[djsynchro]

OK here's the deal: (SA-1) Just found this:

In series with the deep crash button solder something like 100 ohm pot.
I didn't have one, so I got 1k with a 100 ohm resistor in parallel=110 ohms I think

Now the Glitchcontrol works in conjuction with the voltage drop!

Turn it up a little, press the deep crash, nothing happens. Now turn up voltage drop a little, and the SA-1 will start crashing. (Or just turn the Glichcontrol up further)

It really expands the amounts of sounds you get. Also without this trim a lot of the times the crashes will be silent. Not with this bend, you can set it so you get a good crash all the time. Also, at some settings now it will glitch when you press the deep crash button, but recover when you let go of it.

I say essential SA-1 bend, go for it.

Have fun!

[nochtanseenspecht]

thanks ! nice one. i will try it out soon. i'm also still a fan of your sa1 distortion mod !

[djsynchro]

This is the essential killer one!!!
Let there be no doubt: You HAVE to install this one it improves the SA-1's glitchability tenfold.

For example, depending on the knob settings and the selected preset, now sometimes I get non stop glitching,
and pressing the deep crash button keeps changing it (Instead of crashing the SA silent)

Let me know if you get it going & how you like it!
  

[Orangery]

... sounds great but I'm having trouble with the voltage crash on my SA-20 (similar to a SA-21).  I'm using a 470 ohm pot which is too sensitive.  I've heard it works best with 200 ohm pot (or less).  Is the voltage crash worth having?

[djsynchro]

Is the pope a catholic? You GOT to have the voltage crash. I used to have 1k, now solderd a 500 ohm in parallel so that's 500 ohms, works fine. try 200 (or just try wiring some resistors in parallel.

You gotta git da voltage dawn boyyyy! 

[andy_wheels]

i've also found the voltage crash to be quite sensitive and prone to just turning off rather than crash in a nice way.

i reckon the way forward could be one of those small preset pots that you set and leave. set it to a nice crash setting and then it'll do the same thing every time. could even be triggered by a switch.

[djsynchro]

Can I politely disagree? The Voltage drop, Scream & Deep Crash trim pots I have all work together.
They all have small ranges where the glitching will be changing so you really need to have them on pots.

It's true that you don't really get a nice long smooth run where the glitching will fade in, but hey it's not an analogue volume control or something, it's a short circuit.

I have just built another SA-1 as a present for someone. It has a "version 1" board, made in Japan (Mine's version 3 made in Korea) 220 Ohm for Deep Crash trim, 2200 for Scream, 500 ohm (1k with 1k resistor in parallel) for voltage drop. Works great with fresh batteries. Still fiddly to operate though :-)

[Orangery]

I've calculated that a 470 Ohm pot and a 1400 Ohm trimmer should work nicely for the voltage drop crash but... they have to run in parallel... so what does that mean, one wire split halfway up with a pot, trimmer in each then rejoin?  I used two separate wires for each of the variable resistors but it didn't work as I expected it to.  Am I going about this the wrong way?

[nochtanseenspecht]

@ djsynchro ; i followed your instructions (100 ohm pot in line with the deep crash) and you're right,
it is a must have !! my sa1 keeps crashing in a nice way at a certain setting. nice one , thanks !
most loops i've heard before, but i dont need the reset knob nomore.
btw, i just opened a realistic concertmate 970 : it seems to puke out the same loops as the sa1 if i crash it (?)
but in stereo with chorus ! (the soundchip is named m6387-08)

[djsynchro]

I've calculated that a 470 Ohm pot and a 1400 Ohm trimmer should work nicely for the voltage drop crash but... they have to run in parallel... so what does that mean

One wire to the centre connection of the pot, one wire to one of the outer connections (This is clockwise/anticlockwise, I have mine so clockwise increases resistance -->> and brings on the crash)

Resistor from center to the same outer connection as the wire. Now some electrictity runs thru the pot, some thru the resistor-->> Parallel!