Chaos machine mod for use with bass?

ficelles

Member
I've built my Chaos Machine and just got it working after a minor build issue, it's a great pedal but reduces lower frequencies of the dry signal and I'd like to use it on bass... looking at the schematic I am thinking that IC2.2 along with C4, R7 and R29 are making an active high-pass filter with a cutoff frequency around 72Hz and if I double the value of R29 that will take cutoff down to around 36Hz. Only issue is it's also acting as high pass for the two resonant filters so I guess I'd have to be careful of extreme filter settings... has anyone else modded this for use with bass?

[Edit] Thinking again, maybe I could get the same result by changing C4 which would only affect the dry path... 220nf looks like a good value.
 
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skuddington

New member
Hey, I've just finished my first pedal, I play bass and was having similar thoughts. I think alot of circuits just cut bass by their nature, as lower frequencies are just more dc-like and an ac circuit doesn't deal with them well. Lot of commercial pedals get around this with a clean blend knob- mix in some unprocessed input to reintroduce the lost low end. I've not gotten as far as figuring out what that should look like. I think a simple double gang pot wired the right way should work, but to make it usable you might have to also have a level control for the wet signal, or put it after the volume put, at which point you don't really have a volume control anymore... Might work like a dg alpha omega at that point
 

skuddington

New member
I've had a look at the schematic for the chaos machine, and I'm no expert, but if the Dry knob doesn't let you get enough low end into your signal, i.e. if you want more low end in the "wet" signal, i think thats going to be alot of work. For reference, the clean blend i was talking about can be seen in the schematics for the obsidius drive, signal is taken from the input buffer, mixed into the drive signal coming from the drive level pot on a B100K, and then fed into the output filter. The dry knob on the chaos machine is not doing exactly that, but is doing something similar. Id love to see if its possible to mod the wet signal for more low end!
 

ficelles

Member
A the moment I'm experimenting with a buffered blend circuit from FuzzDog, not quite there but I think it will do what i want.
 

ficelles

Member
Happy to say this is fixed with an offboard mod... I have dropped the dry pot from the Chaos Machine and in its place is the blend pot from a Fuzzdog Blender pcb. I had to experiment with pot values as the recommended 100k pot didn't work well but a 10k pot is giving me ideal results. This pedal is now very usable for bass.

IMG_2568.jpeg
 

Chuck D. Bones

Well-known member
C3 and C4 limit the bottom end in the dry signal path. Bump them up to 470nF or 1uF and you should have plenty of dry bass signal getting thru without having to resort to an off-board mixer.

You could play the same game with C5, C6, C14 and C15 in the wet signal paths, the only caveat is there may be some LFO bleed-thru if you increase those caps.
 

ficelles

Member
C3 and C4 limit the bottom end in the dry signal path. Bump them up to 470nF or 1uF and you should have plenty of dry bass signal getting thru without having to resort to an off-board mixer.

You could play the same game with C5, C6, C14 and C15 in the wet signal paths, the only caveat is there may be some LFO bleed-thru if you increase those caps.

Already tried C3/C4 with no success, my guess is the LF loss is happening between IC1 and R5. Anyhow with the blend circuit now in place I'm going to stop experimenting, but I'd be interested to hear if anyone finds an onboard fix sometime.
 

Chuck D. Bones

Well-known member
The dry path & mixer parts of the circuit are easy to analyze. My recommendation should have worked. Any parts subs, intentional or otherwise?
 

ficelles

Member
It was a 100% stock build and works perfectly except for the LF loss in the dry path. I also thought C3 / C4 would have the desired effect and if you calculate the relevant cutoff frequencies that would seem to support that idea, but swapping those caps out didn't have any effect - hence my thinking that the LF loss must be occurring earlier on. I'm not going to do any more mods to my build but maybe the next Chaos builder can try a few options before their board is in an enclosure...
 
Thanks for the great thread posts folks. I'm experiencing similar problems with the Bigger Muffin Fuzz, no lo end for my bass guitar. It as nice to gain a little info here about capacitors and changing their values.

Thanks,
 
Happy to say this is fixed with an offboard mod... I have dropped the dry pot from the Chaos Machine and in its place is the blend pot from a Fuzzdog Blender pcb. I had to experiment with pot values as the recommended 100k pot didn't work well but a 10k pot is giving me ideal results. This pedal is now very usable for bass.

View attachment 10490
Let's see the front of this beauty. Is that the buffer in the lower left just to the left of the 3PDT?
 

Feral Feline

Well-known member
If the Dry pot is wide open, it's effectively running C3 & C4 in series, which would drop the collective capacitance to 50n, no?

I don't have the Chaos Machine, but now I want it so I can slam 2µ2 film caps into C3 & C4;
then socket C5, C6, C14 and C15 and keep pushing those values up to the point of bleed-through then back off to the next cap size down before it bled through.
 

ficelles

Member
Let's see the front of this beauty. Is that the buffer in the lower left just to the left of the 3PDT?
It's the blender circuit, but an onboard mod would be far better if someone gets one working... I probably didn't try enough alternate cap values.

Front view is very plain, just black with purple knobs.
 

ficelles

Member
If the Dry pot is wide open, it's effectively running C3 & C4 in series, which would drop the collective capacitance to 50n, no?
I'm probably reading this wrong but it looks like C3 + 100K dry pot is making a simple passive RC hpf, and C4 with R7, R29 and IC2.2 is making an active hpf... not sure though how the filter inputs though R8 and R28 might affect all that.

Disclaimer: I am no electronics engineer so feel free to shoot my limited knowledge down in flames :)
 

Feral Feline

Well-known member
Using Orman's calc, http://www.muzique.com/schem/filter.htm, the C3 & 100k Pot gives a corner freq of 15.9Hz and turning the pot down to 1k gives 1592.4Hz — but then it goes through C4...

Please forgive my ignorance, but I still don't understand C3 & C4. Seems redundant. Why not just jumper one or the other? While contemplating that, I noticed mix A and B are the same dealio:

Op-amp > 100n Cap > B100k Pot > 100n Cap > R10k


When I suggested in my previous post of pushing the values of C5&C6 as well as C14&C15, I hadn't yet noticed they were exact copies of the order indicated above. So in each case they're blocking bass big time with series caps giving just 50n. Every step is blocking bass, not just the clean signal.
 
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