messing with an arion moc-1 (boss oc-2 clone)

[Quackzed]

i just scored an arion moc-1 cheap on evilbay. It sounds pretty good on its own. 3 knobs ,direct signal vol, 1 octave down vol, and 2 octaves down vol.
both octave signals are pretty heavily filtered and volume wise neither is as loud as the bypassed signal. while the 1 octave down is only a few bits below unity when cranked , the 2 octaves down signal is pretty low volume. so it would be too quiet to use on it's own. though its loud enough to beef up the low end behind the other signals...
and the filtering does a good job of getting the oct 2 to sound round and 'bass like' ...
    i found most of a schematic ...it's pretty big but heres a link.
http://files.effectsdatabase.com/docs/schematics/arion_moc-1_partial.gif
   so i wanted to try and get more volume from the octaved signals first...
ic1a has a 10k in its feedback loop ,so i increased it for more gain and settled at 57k .
at 100k it was too noisy and distorted but at around 57k it sounded much louder (oct 2 around unity now) without any bad noise or distortion, or affecting tracking.all signals are louder now. cool.
    now i'm trying to tackle those low pass filters right before the octave output pots... not having any luck, i tried cutting c9 on oct1 but it was adding noise and fizz as well as brightening up the signal, c10 removed from oct2 gave me no signal at all for oct2...
i'd like to get it to where i could add a swich to go from 'filtered and basslike' to 'mostly unfiltered' and synthlike buzz.
any ideas ?
maybee smaller caps at c9 + 10?

[Quackzed]

aha! mr. butterworth's ahead of it's time filter... sad he was overshadowed by his delicious wife's syrup. 

wikipedia says...

Butterworth had a reputation for solving mathematical problems that were thought to be impossible to solve. His paper was far ahead of its time and the filter was not in common use for over 30 years after its publication. At the time filters were largely designed by trial and error because of their mathematical complexity.

so it looks like a 2nd order sallen-key type butterworth low pass filter,i think i can reduce the 330k resistors to say 100ks for a rolloff at @1k instead of @ 300 ?ish.. i'll have to try it out and get back...

[stringsthings]

Sally Butterworth:  Honey, I've making some pancakes for breakfast.

Stephen Butterworth:  Not now, baby ... i'm inventing a filter !

Sally :  ( sigh )

..................

later that evening ...

Stephen:  hey, Sal?
Sally:  yes, sugarcakes?
Stephen:  what's this sticky stuff all over my workbench?

[Quackzed]

 
   well, i messed around with the filter a bit, the circuit had 2 330k resistors, so i tried 100ks in r16/r17 (brighter with a bit of buzz) then bypassed the 2 330ks entirely(full bore buzz) in the end i went back and forth between jumping just one 330k r16(half bore buzz with alot less fizz and noise) and jumping both, and decided that jumping both wans't as usable due to too much noise and fizz... so i added 2 spst switches.
1 jumpers r16 and the other jumpers r25, for a more trebly and synthy tone for 1 oct down (r16) and 2 oct down (r25)
so in all...
cut c7 for a bit brighter tone for oct1
cut c11 same for oct 2
changed r8(10k) to a 57k
and added 2 switches:
1 jumpers r16 for a buzzier oct1 sound
1 jumpers r25 for a buzzier oct 2 sound.
i was thinking of adding an octave up to it, but i couldnt decide which, now i'm thinking of maybee adding an fx loop deal... to insert an extral parallel stage to blend in with the octaves..hmmm...

[stringsthings]

awesome .... any chance for sound clips? 

octavers are neat .... have you checked out Craig Anderton's Roctave Divider for ideas?

http://hammer.ampage.org/?cmd=lt&xid=&fid=&ex=&pg=12

[Quackzed]

yeah, i'll try and put some soundclips up in a few days. not sure where to host em... if anyone has any advise...?
octavers for some reason, make me want to play funk.  i/ve been playing weird funky riffs through this thing all day...
i'll bet my neigbors are sick of my modding noise  by now..
rocktave looks like a great diy down octaver along these lines, fuzzed up and synthy. between the 2 switches and all the blending options this thing has a ton of tones. ill have a hard time deciding what the core tones are for the soundclip. 
i'm bringing it to an open mic tonight, to see how it sounds at stage volume. 

[stringsthings]

i like Soundclick for audio .... http://www.soundclick.com/default.cfm

core tones?  anything goes ! 

[Quackzed]

so i plugged this thing into my twin at a decent volume the other night, and it was a little scary. the low end of this thing is huge! at bedroom levels it was pretty low, at room levels i was afraid it was gonna hurt my speakers!!! i seriously clicked it on and whoa... the 2 octave down signal was making the whole drum kit vibrate, i turned down the 2nd octave fast. but its cool that it has so much low end available now, more than too much really. otherwise its fun to play through. with the direct signal off and just the 1 + 2 octaves on and set for unfiltered they blend really well and each at very low settings just sort of adds texture to the louder octave before being destinguishable as a second voice. still enjoying this thing...

[Quackzed]

just a little revision, turns out, my ic1a resistor change 10k to 56k was fine for my single coil guitar, but my humbucker guitars are pushing it into distortion, so maybee leave the 10k alone... or up it only to 22k ...
anyway i figured i'd post it for posterity...

[charmonder]

hi im really interested, im not sure if youve seen these videos but someone out theres got his boss oc-2 modded up pretty well
http://www.youtube.com/watch?v=LobWtFAtS1Q
http://www.youtube.com/watch?v=up5SKmEOZeI

basically hes found jumper points so you can make in the circuit to bypass the filter like you have, and also theres one to bypass the envelope which makes the synth track the volume of the guitar.

Im assuming there are direct parallels to the moc-1, that schematic you posted is that only a partial schematic? does it have everything I need to figure out where those jumpers need to be?

[Taylor]

hi im really interested, im not sure if youve seen these videos but someone out theres got his boss oc-2 modded up pretty well
http://www.youtube.com/watch?v=LobWtFAtS1Q
http://www.youtube.com/watch?v=up5SKmEOZeI

basically hes found jumper points so you can make in the circuit to bypass the filter like you have, and also theres one to bypass the envelope which makes the synth track the volume of the guitar.

Im assuming there are direct parallels to the moc-1, that schematic you posted is that only a partial schematic? does it have everything I need to figure out where those jumpers need to be?

If you check out the octave down circuit on my site (link in signature), in the PDF I explain how to tap into these other signals, make the filter variable, etc. It's written for my PCB, but the info can be applied to the OC2 or other similar circuits.