experimental scope - poking the x0xb0x

[antto]

but it needs all the knobs and buttons and leds
to be precise..
Venom has 24 buttons (exactly positioned as on the 303) and all of them have a LED (unlike the 303) plus the 16 "bank" leds as on the x0xb0x
tempo and volume pots, bank (16 positions) and mode (12 positions) switches, and the 6 "performance" knobs
ehm, here's how it looks now (it will change a bit, and the LCD is not shown here)

so i think it shouldn't be smaller than the actual 303

[antto]

...now i gotta fix my x0x
during all of this, one of R36's legs got ripped off (thus no square) and J6 got stretched, needs a new cable..


fortunately i have more desoldering wick

[guest]

those original cables really sucked
but there wasnt a big selection back then

[antto]

finished up the whole section
i also figured the "E" coefficient can be used to perfectly mimick TM3
in my case (with the x0x) the "E" coeff goes from -2.36 to -0.56

i also approximated the effect of the envelopes going a bit up and down with a dedicated LPF
and the c36 envelope which feeds to the VCA on accents
got the pot response curves for the cutoff/envmod (almost identical) and the decay (slightly different)

now it's indistinguishable from the x0xb0x

guest, thank you so much!

here's a comparison (both synth's sync'ed together via midi) side to side
http://www.box.com/s/8f512c6137bfaeb384a7 (mp3)

[antto]

..i also approximated the effect of the envelopes going a bit up and down with a dedicated LPF..

i was wrong again
this effect comes from C13 itself, envelope bleeds into it at all times
so, i guess that's all about the envelope section

[guest]

sounds great
if i had to guess
id say the x0x was on the right
but i cant really tell any difference

so whats next

[antto]

yeah, the x0x is on the right
for some reason the midi sync to the x0x is a bit "jumpy" i'm not sure why.. maybe it's due to my lousy firmware (some notes might take too long to process)

from the envelopes section - everything is working correctly, except for the VCA attack
the "clicky" thing as you know from the other thread, it's some diode charging up the envelope
in my synth - i just use a LPF, but i set it's attack frequency to fast enough, so it clicks as much as my x0x
that's a minor thing..

what's next?
there are 3 things left in the synth - the sequencer (which is not finished yet) the VCO and the VCF
i will probably revisit the VCO..
i really wanna calibrate my square to a 303, because i still think there is some difference
and the VCF is almost perfect, i just need to do a few more tests

for now, i'll post some plots of the potentiometer curves

[antto]

for the green curve, i don't remember whether i measured the cutoff or the envmod pot (i used my multimeter) but it works for both
the other two are quick approximations, and are not very accurate around the "ends" but it's good enough for me


and this is the naive approximation of D24
i use this to shape the signal from IC12 which is the (main_envelope * ACC) * accent_pot
in my case that signal is in range 0 to 1.0
it's accurate enough, i can tell from the sonogram, i boost my resonance mod to max (R97 to 0Kohms) and then decrease the resonance pot, which makes more of the unfiltered signal to go around C13
this unfiltered signal is exactly the output of D24