madbean colossalus aka mxr flanger power supply

[tabbycat]

hey debugging freaks,

am fairly clear about a power supply issue with the collosalus (am using the madbean 2012 pcb, savvas has done a layout for the 2015 here http://guitar-fx-layouts.42897.x6.nabble.com/file/n23859/madbean-collosalus.png) but am confused by a power cap value.

however, there is a slight difference between the 2012 collosalus and the 2015, in that the 2012 used only a lt1054 charge pump to bump 9v to the standard 18v for this cicruit, whereas the 2015 offered that but also a switchable 18v direct in option.

from comparing the 2012 and 2015 power input sections, and savvas's vero (which omits the optional lt1054 charge pump in the 2015 layout and is 18v in only) it seems i just have to put the 18v straight into the 7815 regulator input, bypassing the lt1054 option entirely. seems obvious enough.

but i notice there is also a cap value difference immediately after the regulator, between the 2012 and the 2015 versions. the 2012 regulator is directly followed by a 10u cap (c26) and the 2015 by a 100u cap (c27) which is quite a big difference.
i think there were reported noise issues from some builders of the 2012 design, thought to be due to the use of the charge pump. could that be why the 100u appears in the revision? increasing the value of this cap by 10x seems a big leap. yet the rest of the circuit seems unchanged.

so basically, should i go with the 10u or the 100u? i have already populated board before thinking about direct in 18v (i would actually prefer direct in 18v) but not a problem to remove and replace. if i'm bypassing the lt1054 then potential noise issues are not relevant.

what do you recommend?

as this is my biggest build to date i don't want to blow it up, so while i might be gung-ho and play around with a more expendable build, i'm verging on caution with the power in on this.

[strewel_peterson]

I think those cap changes are most likely belt-and-braces extra smoothing : the 2016 layout also ups the caps to ground before the regulator to 470u in parallel with 100n, which is something I've seen before (I think the different characteristics of thectwo caps address different kinds of noise?).

Safer to wait for more answers, in case I'm wrong, though.

[tabbycat]

strewel_peterson wrote

I think those cap changes are most likely belt-and-braces extra smoothing : the 2016 layout also ups the caps to ground before the regulator to 470u in parallel with 100n, which is something I've seen before (I think the different characteristics of thectwo caps address different kinds of noise?).

Safer to wait for more answers, in case I'm wrong, though.

thanks for your thoughts on this one, sp.

am wary of getting it wrong and ending up with noise that makes it ususable. can get away with a bit of noise on a fuzz, just disappears in the chaos, but modulation seems to exaggerate it in a grim way. on the other hand would going from 10u to 100u be overkill?

what happens before the regulator is not so much of an issue as i want to bypass that whole thing and just go straight in with 18v (as in savvas' layout).
he uses a 100u and has had good reults with it, so maybe that is the one.

i'm just being tentative as this build has a billion ics that would be annoying to burn out if overpowered.

[ξεναγος νεκροπολης]

hi there tabby!
saw your post yesterday but i was in work.
if you want to use a 18v supply all the time, i would suggest to use everything from 470uf to right of the 2015 power supply.
mine is surprisingly quiet and i really think that using a 18V supply for that effect and only helped a lot with that.

[tabbycat]

ξεναγος νεκροπολης wrote

hi there tabby!
saw your post yesterday but i was in work.
if you want to use a 18v supply all the time, i would suggest to use everything from 470uf to right of the 2015 power supply.
mine is surprisingly quiet and i really think that using a 18V supply for that effect and only helped a lot with that.

hey savvas, i thought about you today as i was reading this http://www.theguardian.com/commentisfree/2016/may/09/the-choice-for-europe-rescue-greece-or-create-a-failed-state paul mason is one of our better journalists. i hope you're surviving ok.

re the mxr collosalus, many thanks for the clarification re the 18v network. damn, i was hoping i could get away without that 470u as there is no way it's going to fit on the board. will have to stick it on a daughter board with the 100u and patch that into the pcb. maybe i'll get a lt1054 and try it with the charge pump just in case that isn't so bad, but obviously 18v straight in is always going to be best.

what do you like hate about your build? have you modded it at all?