# Chaos Machine siren issue



## Solderaddict (Aug 14, 2020)

So I’ll get right to it, I have a strange issue with my Chaos Machine. 
When testing everything worked fine all knobs to min/max so in the case it went. 
Since playing it I’ve discovered that if the intensity and resonance settings on either filter (resonance seems more significant) are turned too high the circuit cuts all input signal and just wails this clean continuous siren sound, which changes depending on where the LFO rate is set.
The same thing happens if the signal input is too hot, ie a hard guitar strum or high volume.
When the resonance and intensity knobs are full then the thing is unusable as it just nee naws as loudly as it can - I’m concerned as it sometimes does this out of nowhere and this makes it unreliable for live gigs. 
It works beautifully (even the hissy filters I like) if treated gingerly and both resonance pots are kept low but I think this instability is a sign of something wrong in the circuit - I’ve tried changing the filter ICs but not the LFO ones yet. 
I wondered if anybody else has this issue with the Chaos Machine or any other project with LFO and filters - any insight would be greatly appreciated!


----------



## Robert (Aug 14, 2020)

It's hard to say without hearing it, and I can't recall if the prototype did this or not, but most high-resonance filters will self-oscillate if you crank the resonance control up all the way.       

It's how I tuned the frequencies for each step on the Daydream, in fact.


----------



## Solderaddict (Aug 14, 2020)

Robert said:


> It's hard to say without hearing it, and I can't recall if the prototype did this or not, but most high-resonance filters will self-oscillate if you crank the resonance control up all the way.
> 
> It's how I tuned the frequencies for each step on the Daydream, in fact.



Self oscillation was my first thought but I feel like it’s less like the self oscillation I’m familiar with (delay and feedback looping). I’ll try to get a recording to post so you can hear what I’m on about.
The sound is hard to describe but it’s like an intense siren which seems to switch on abruptly and sometimes off by itself if caused by a hot signal.


----------



## Robert (Aug 14, 2020)

An oscillating filter sounds a bit different from a delay or reverb in self-oscillation.

Here's an example of a bandpass filter with the resonance cranked up too high.   (Be careful, this can be rather loud and high pitched)
https://soundcloud.com/pedalpcb/filteroscillation


----------



## Nostradoomus (Aug 14, 2020)

That’s what makes the Earth Sound Research Graphic Fuzz fun!

Skip to 4:00


----------



## Solderaddict (Aug 14, 2020)

Robert said:


> An oscillating filter sounds a bit different from a delay or reverb in self-oscillation.
> 
> Here's an example of a bandpass filter with the resonance cranked up too high.   (Be careful, this can be rather loud and high pitched)
> https://soundcloud.com/pedalpcb/filteroscillation


See it kind of sounds like that except the sound doesn’t grow from any input source, rather it suddenly cuts in and out of the mix and all other signals are cut out. Watch this space I’ll get an audio clip sent over when I can - thanks for the input though, it definitely helps!


----------

