[sdiy] First DIY synth (555 osc.'s)

[Scott Gravenhorst]

Take a look at the specs for an ICM7555.  It's a drop-in
equivalent for the 555, but CMOS.  The data sheet says that
there is no crowbar effect during switching as there is
in the bipolar version.  They show a scope trace of each
part during switching and the difference is stunning.  The
LM555 consumes 3 ma with a 5V supply, where the ICM7555
draws 50 _micro_ amps at 3 volts and 180 microamps at 16
volts.  So for a battery operated device, the ICM7555 is
a much better choice.

">>>marjan<<<" <urekar.m at EUnet.yu> wrote:
>> hmmm, a couple people wrote saying this.  it's definitely possible that
>> it's the battery slowly dying.  i should note i probably overstated the
>> stability. i went away for 15-20 minutes came back and it was
>> signifigantly differing in pitch; octaves in minutes was probably what
>> you might call a fish story.  the battery was dead the next day.  in any
>> case, what do i know about stability anyway?
>
>My first synth was based around 555s, and in the start I had them
>powered
>from 9V batt (or two large 4.5V ones) but 555 has large current peak
>while changing it's state, wich strucks battery very hard, and I think
>no matter how new batt is it'll drop the voltage during transistion
>and batt will recover from it in some finite time, so rail transients
>affect the stability in large scale. You can make it better by
>decouplong
>rails with 10-100n ceramic cap near the chip plus to coonect pin 8 thru
>100ohm res and 100uF cap to gnd, while using regulated power (at least
>78xx or zener+transistor), battery is inconvinient here.
>Chip itself shouldn't be worse performer than resistor used. Second
>source of unstability is charging cap. First I used any I had, most
>of the time ceramic (disc). Using poly showed to work better in overall
>range (audio), but then I had no idea why...
>
>I used to prefilter square out (both audio and lfo) with small
>RC constant to tame a little those squares as they are wery sharp
>and made all sorts of ringings and bleedthrus around in my system.
>Use some opamp or transistor buffer if you use "triangle" out
>from the cap (it's rather sort of expo triangle).
>
>
>marjan


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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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