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Filter warble? Check your power input.
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by phono on Wed May 28, 2008 9:17 am

reflowed r95, c28 then additionally c30 c29 c22 c16

problem still persists :S, perhaps c28 is bad? r95 is fine, measured 100 ohms
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Re: Filter warble? Check your power input.

by phono on Sun Dec 21, 2008 5:31 pm

well time to bring this old one up since i never solved this on one of my xox.

I've tried all the mentioned things throughout the forum and it seems the warble isnt related to those issues. I did just make a discovery and that is that if i max all the knobs except decay the warble never starts, but as soon as i dial in 50% on the decay (all other knobs still maxed) the warble starts almost instantly and stops almost as fast when i bring the decay back to 0%.

perhaps the warble is related to the decay circuit in some way, can any of you suggest what i could check in this area to eliminate this dreaded warble once and for all.
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Re: Filter warble? Check your power input.

by guest on Sun Dec 21, 2008 6:14 pm

do you have an oscilliscope

it might be worth looking at the 12v and 5.333v rails
when the warble is happening
and see if they are moving around any
that would at least eliminate the powersupply as the issue

otherwise one of the cvs to the vcf is acting up

does the envelope work fine elsewise
does it sweep the filter
and change decay times
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Re: Filter warble? Check your power input.

by phono on Sun Dec 21, 2008 7:34 pm

guest wrote:do you have an oscilliscope

it might be worth looking at the 12v and 5.333v rails
when the warble is happening
and see if they are moving around any
that would at least eliminate the powersupply as the issue

otherwise one of the cvs to the vcf is acting up

does the envelope work fine elsewise
does it sweep the filter
and change decay times


i dont have a real scope unfortunately, everything else works as expected, the envelope seems fine also. The last time i tried finding the fault i remember reading c28 with a volt meter and it was constant with or without warble. It definately seems in some way related to the decay knob though, (with all other knobs maxed) since i can now dial up warble at will, still i've no idea if that gives you any idea as to what i should look for to fix this.
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Re: Filter warble? Check your power input.

by guest on Sun Dec 21, 2008 8:35 pm

its going to be difficult to find the problem
without a scope
as the issue is a time varying one
so the dc values may not be changing
and just have some ac signal coupled to them

its worth a try to measure the 5.333v and 12v with a voltmeter
even if they dip by 10mv when there is warble
that might indicate something

you could also measure other critical areas with and without warble
c29
c22
c16
c30
the drop across r69
but im not sure it will show anything
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Re: Filter warble? Check your power input.

by phono on Mon Dec 22, 2008 6:59 pm

guest wrote:its going to be difficult to find the problem
without a scope
as the issue is a time varying one
so the dc values may not be changing
and just have some ac signal coupled to them

its worth a try to measure the 5.333v and 12v with a voltmeter
even if they dip by 10mv when there is warble
that might indicate something

you could also measure other critical areas with and without warble
c29
c22
c16
c30
the drop across r69
but im not sure it will show anything


thanks i'll give that a go soon as i get a decent amount of free time to get inside without interuption and i'll post up my results, my meter is kind of cheap so it might read a bit slow, but still its worth a shot since this is really something i'd like to eliminate once and for all
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Please be positive and constructive with your questions and comments.