556 lfo

[noystoise]

im wondering if anyone can help me out, i built a very simple lfo with half of a 556. the problem is that im getting clicking sounds from it even when the output is not connected to anything. i feel like ive had this problem before and somehow figured it out, but for now im stumped.

any ideas?

[LoFi-Ninja]

Have you tied the unused inputs to ground ? Maybe that would help..

[Matt the Modulator]

are you taking the output straight from pin 9? if so try passing the output through a 1UF cap with a 1 meg resistor to ground i could be wrong but i think i sorted out a problem similar to this doing that good luck !

[Gordonjcp]

It's because 555s and by extension 556s are shit.  They suffer terribly from shoot-through, which is where both output transistors are on momentarily thus shorting out the supply rail.

Ghastly things.  Use the CMOS 7555 instead, it's still crap but nowhere near as fatally flawed.

[noystoise]

It's because 555s and by extension 556s are shit.  They suffer terribly from shoot-through, which is where both output transistors are on momentarily thus shorting out the supply rail.

Ghastly things.  Use the CMOS 7555 instead, it's still crap but nowhere near as fatally flawed.

unfortunately for me i think you're right on. i've tried every possible solution i can think of but the click is still there. i'm using the other half as a one-shot, it sort of does the same thing but its really not that bad. i think i have a 7555, maybe i'll use that for a one-shot and use the one left over opamp on the 324 i'm using for the lfo. thanks for the input.

[Gordonjcp]

What might help you is decoupling the supply to the 556.  Use a resistor somewhere between about 33 and 100 ohms in the positive supply, and then a biggish capacitor maybe about 100uF to ground on the 556 side of the resistor.

[noystoise]

thanks but that doesnt work either. it wouldnt be so bad if it only clicked in the high state but it clicks once on high and once on low state too. all i need this lfo to do is trigger a 8-step sequencer and/or the AR generator. i think a simple back feeding comparator will do the job fine with that left over op-amp in the 324 i'm using.

[Gordonjcp]

You could also look at using some sort of logic chip to generate a clock - basically two inverters with an RC network to set the pulse delay.

[justindeloop]

It's because 555s and by extension 556s are shit.  They suffer terribly from shoot-through, which is where both output transistors are on momentarily thus shorting out the supply rail.

Ghastly things.  Use the CMOS 7555 instead, it's still crap but nowhere near as fatally flawed.

yeah i second this - 555's tend to screw up other things running off the same power supply for the reason posted above.

i tend to use 40106 schmitt triggers w/ an RC network as theyre slightly simpler to build and dont have this problem.

[noystoise]

so i tried a few other approaches to the lfo but they didnt work out as well. in the end i just went back to the 555 because both the op-amp and logic chip lfo's i tried gave me the same clicking problem. the only difference was that the were too unstable and stuttered. i will explore more options next time. i just ran a .1mf cap from the output to the gnd. this seemed to help a little bit. this is the final product
circuit bent rainbow synth

[Gordonjcp]

Ooh, that's got quite a nice filter!  Is there a circuit diagram for it anywhere?  What's inside it?

[noystoise]

heres my schematic.

the filter is just a rendition of the MFOS WSG filter. im not really sure what kind of filter it is actually called.

[SineHacker]

good job!