SA-2 notes, pt.II: the Amp

since i was using this old record player, i wanted to keep the original speaker and the original 500K pots.
as an exercise, but also because the construction of pots/shaft/knobs on them is not easily replaced.

first thing i tried was a ruby amp.
that didn't seem too happy about the speaker i wanted to use.
out of the parts bin came another contestant: the LA6500.
it would need a bipolar supply for extra headroom/volume, but i can live with that.
has the added benefit of not needing coupling caps -added one at the end for speaker protection, but don't think it's really necessary.

so i put in a transformer to power both the amp and the keyboard from the mains.

no more wallwart!

some moons of testing later i installed this:

* a 071 preamp, with a fixed gain of about 700%.
the first pot (originally the tone control) is taming the input.
it can still do clean sounds, but when the output is hot enough, the signal gets clipped by a pair of back to back yellow LEDs. sounds really nice, and the signal never exceeds 4 - 5Vpp, which is very reasonable for the poweramp.

* lowpass, taking off some clipping harshness

*LA6500 poweramp, with the second pot acting as a master volume.
slightly amplifiying the signal further, and providing enough current for the speaker.

i mounted the LED clippers in front of the speaker, the cone of which i sprayed white.

now the speaker 'lights up' when the signal is clipping, which looks as ridiculous as that gooseneck led.

all in all it sounds great, looks nice and it's plenty loud. 

not complaining.

SA-2 notes, pt.I: the keyboard

alrighty
the lowdown.

the keyboard happened to fit exactly in the case of a broken 60's philips mono record player.
that means any bends and mods were no longer restricted to the size of the SA-2 case.

for mods and bends, i went digging through too much info on the Circuitbenders forum and over at CasperElectronics, where i found a neat SA-7 schematic. turns out to be almost 100% identical to the SA-2.
different clock crystal, and a cap more or less, minor stuff.

sound selection is normally reduced to Tone 0, 1, 2 and 3 buttons.

now, some extra poking and wiring can complete this matrix:

that's all 100 SA-1 sounds, 5 drumsounds and possibly 5 demotunes.
more on that here.

with an old school pushbutton switching array, i wired up essentially a 5PDT switch.
in one position, you get all 10 sound select buttons,
in the other, the bottom 5 are the drumtriggers - the top 5 create random glitches by injecting the amplified audio back into datalines 11, 12 and 13. that would be the first true bend, strictly speaking.

next, i tried the Reed G. aleatron crash mods, but felt it blacked out on me way too much.

fun for recording samples or whatever, but for playing it live it was just too fickle. so: decided to crank that bend up a notch.

since the crashes depend on throwing the clock out of whack - so the little darling doesn't know where it is in its program anymore - i was looking for a way to interrupt the clock stream with more precision than the standard Aleatron mod offers.

enter CMOS.

took most of the puzzle pieces from the excellent MFOS website.

(scroll down to Synth DIY 101 - MickeyMouseLogic.)

look at the top two inverters: first one debounces a momentary switch so we get a solid ON signal.

second one turns that push into a fixed length pulse, no matter how long you hold down the button.

that pulse then triggers a 4066 analog switch, very briefly connecting (in this case) C11 on the casio board to ground, through a 47R resistor.

i tried putting the pulse length on a pot, but it doesn't actually seem to make the crashes all that more intense.

you just get to a certain point where it will just crap out on you (until you reset the power, that is.)

the whole thing does seem dramatically more stable.
maybe a bit less drastic on the glitching side, but it will still do the odd aleatoric tune every now and then, which is my main goal anyway. and it crashes a LOT less.

so, two crash buttons (and a power reset button).
as seen on the schem, i found a pitch bend as well. it actually works best when it is spitting out glitchy loops already - taken too far in normal mode, it will start to behave erratically and not recover.
since i was using that 4066 and 2 crash points are also in the pitch bend, i just wired that one up there as well.

that left me with one inverter on the 40106.
oscillator! LED driver! LDR across pitch bend pot! optovibrato! HAHAAA!
i put a nice blue LED on a gooseneck so i can position it anywhere i want it against the LDR -
looks very ridiculous.

extra stuff: added a distortion bend, running AN8053 pin#5 to OKI pin #5 through a switch + pot, as found on the circuitbenders forum.
the AN8053 pin is a frequency compensation output, basically a double of the amped signal.
the OKI pin is the unamplified audio output.
so we're getting a very crude feedback loop, essentially: amp audio out to amp audio in.
not sure if i like this one so much. might need to try a different pot value (have a 1K in there now.) it does sound great on beats though, adding a kind of filter resonant sound.

it goes especially well together with a frequency shift mod: parallelling the AN8053 pin#6 cap with another cap, or even better - touchpoints. sounds nice, although i think i made the wiring on this a bit too long, adding unstable capacitance and introducing nasty static. have to try a new switch there anyway, so that part's on the ToDoList.

i put a second LDR on a switch, to choose between bridging the distortion pot or the volume pot (i did away with the digital volume control and just added a pot at the speaker wires. not using the speaker, either.)

that makes for either pulsing fuzz or tremolo, when lit by that gooseneck led.

next up: the insert jack.
the OKI output has a jumper somewhere before it gets to the 1.5K resistor. i cut that, and put in a switching jack.
most fx pedals seem to like the unamplified signal better, so there you go: an easy fix to have your cheap Behringer pedals behave more predictably with Casio keys.
minor drawback: the feedback loop does have very different results when faced with fx in there, if it does anything at all.
but hey - i tried the led vibrato with a tape delay in the insert jack..
shit is gorgeous, so pooh pooh.

Norwegian Harvest, Remote Style

The Kunstisizer from Wrap Arts Centre on Vimeo.

this funky performance box is made by the almighty Roar Sletteland, whom i met over at BEK.
it was commissioned by the Wrap Arts Centre, and while i was there it was still in its foetal conceptual stage.

after we were talking about the idea of making an electronic instrument that had a few demands to it
- it had to be simple, because thirty pieces would have to be handmade - anyone would have to be able to play it - portable and standalone - to be integrated on stage in a 'theatre' kind of idea, etc etc -  i actually had a very vivid dream about just such an instrument. it was made for two players facing eachother, controlling each other's sound.

normally i'm not the kind of 'it came to me in a dream' kind of person.
so i thought it was hilarious. still, the idea sort of stuck.

so this is my claim to the Most Esoteric Non-Participation Award of 2011.

the concept survived, although it looks quite different than what i subconsciously had envisioned -
and i have no clue as to what is in there, as far as electronics go.
all i know is i'm honoured to have been (a very small) part of this.
and very curious as to what the participants will do with it.
keep you posted!

Casio SA-2 bend/build report

over a year ago, i started bending my Casio SA-2. 

never really happy with how it was turning out, it got left in one of many corners somewhere.

recently i picked it up where i'd left it.. here's what happened to it, kinda.

standard issue. pic found on the net.

the victim.

bottom: homemade buttons on tactile miniswitches
top: mode select switching array

crash electronics

insert jack top left

tape delay inserted

LFO drives LED drives LDR

new amp, original speaker

amp clipping makes the speaker light up.

End Result (for now)

more explanation, notes on bends, mods, amp etc coming soon.

Norwegian Harvest, pt.III: Arne's Stick Of Joy

dug up the footage of the dual oscillator joystick.
my man Arne S. had bought a noysestick on eBay, but the range was totally limited.
we used the oscillator basis and put it in a nicer joystick, which had a lot more buttons as well
aka more options for mods and bends.

since it stayed in norway, this is all from memory..
i think it houses 2 oscillators on a 4093 IC.
(not entirely sure, because i'd expect 4 oscillators then, but ok.)
each osc pitch is on a joystick axis.
your triggerfinger activates one oscillator,
the other has a momentary on/off button as well as an on/off switch.
master volume control slider on the side.
don't really recall what the two pots on the front do, to be honest.
some buttons switch in different caps for different pitch ranges,
some buttons make the two modulate eachother.
some buttons don't do anything at all.

the keyboard is basically an extra resistor ladder that gets spliced into the pitch control of oscillator 1.
keyboard also holds a bend with an led on one of the slider switches, but i have no idea what it hooked to what.
it did sound nasty though.
i'm sure i drew up a schematic while working on it, but (of course) i don't have that here either.

anyway - it's noisy, irritating and obnoxious. just how we like it.