velleman hack

[turing]

hi, just picked up a little velleman signal generator, with an eye to converting it into a dub siren. trouble is all the useful things like frequency, pitch etc are all fixed.
waveform is easily done, as it's just jumpers that i can replace with a rotary switch. i was hoping that someone with a better understanding of schematics might be able to point out where i can sub in pots and switches, to give as many vaariable controls as possible. here's the schem . http://www.velleman.be/downloads/0/manual_mk105.pdf
any thoughts?

[zjokka]

don't know if you're already hacking you way through that poor kit , if not have a look at this diy dub siren:

http://www.interruptor.ch/dub_diysiren.shtml

haven't tried it myself, but do know there some very useful stuff on making dub on that site. Heavy dub scene in Switzerland, ever since Lee Scratch Perry married some Swiss countess or something.
Can't help on the schematic though, I'm sorry.

Do keep it posted.
ZJ

[slacker]

The frequency is set by the combination of R1, R7 and C3, check out this site for a nice explanation of the 555 circuit used.
If you want to make the frequency variable replace R1 or R7 with a pot wired as a variable resistor. You could also add a switch to add another 47n cap in parallel with C3, switching this in would cause the frequency to half, giving a kind of octave jump effect.
If you want  more ideas have a look at smallbear's tremulous bear trem pedal which uses the same basic 555 layout.

[turing]

brilliant, thanks for the help, i'm off to butcher that poor unsuspecting pcb now. about the interruptor siren......i had stumbled across that before, but was slightly nonplussed by the gnomic instructions. maybe when i'm a little more confident.