Dumb Muff Octave Question

[johnadon]

I'm not sure if what I'm doing is futile or even if it's been done before (correctly). I decided to play around with my Big Muff and insert the Foxx Tone Machine Octave up section just for kicks. I picked the output of the sustain pot as the insertion point for the what I'm assuming is the entire octave section of the Foxx Tone Machine. On GGG's schematic I extracted the parts from Q2 all the way to what would be the sustain input input of the rest of the Foxx circuit, Q3. I included a capacitor between the output of the Big Muff sustain and the Foxx portion of the circuit.

I think it's pretty obvious that I have a biasing problem on the Q2 transistor since I'm getting the sputter typical sputter/splat. Plus I have to turn the sustain on the Muff all the way up even to achieve the sputter. On the Foxx section I'm using the resistor values specified in the  Foxx schematic. I did not include the section in the Foxx that goes from the emitter of the Q1 to the emitter of Q2 and the junction of the diode and Q1 emitter resistor to ground.

I guess my questions are: Is it even feasible to approach the circuit this way or do I have a simple biasing problem on what would be Q2 on the Foxx? Or does it just plain ruin the gain structure of the Big Muff? Would the Tone Machine snippet work better in another section of the Muff, if what I'm wanting to do is feasible? And I guess I should ask the obvious: Is there already such a circuit in existence? I haven't been able to find one.

Thanks for any opinions!

[aron]

John,

I would try this.... check out how Gus did the octave up with transformer. Put that at the end of the Big Muff!!! I wish I had tried this.

http://www.diystompboxes.com/pedals/SOU2.GIF

[El Heisenberg]

John,

I would try this.... check out how Gus did the octave up with transformer. Put that at the end of the Big Muff!!! I wish I had tried this.

http://www.diystompboxes.com/pedals/SOU2.GIF

wow, thatd be a pretty simple and usefull add on to the big muff. I have my Fulltone Ultimate Octave clone, and like it. But i've always thought the green ringer before or after the big muff or another distortion sounded way better.

A big muff with an extra foot switch, to turn on an octave like that would be simple. That's the way the tychobrae gets the octave. It's my least favorite sounding octave tho. But simpler than putting switchable a green ringer in front or after it. Next Big Muff I build is gunna have the transformer octave.

[Processaurus]

I did not include the section in the Foxx that goes from the emitter of the Q1 to the emitter of Q2 and the junction of the diode and Q1 emitter resistor to ground.

You got the circuit fragment end right, the cap to Q3, but you answered your own question almost, you need the entire front end, from the circuit input to Q3 to get the famous Foxx octave.

http://www.generalguitargadgets.com/pdf/ggg_ftm_sc.pdf

I would put it on the front end of the muff, and true bypass it.  Maybe use a trim pot to attenuate the foxx output (the "sustain" pot), to match the gain of the non foxxed signal.

[johnadon]

Thanks much for the replies. I like the Foxx octave sound considerably better than the Tycho Brahe, but I long ago cannibalized my Octavia build for parts because I wasn't that fond of it. Since I've  already got a Tone Machine running before my Big Muff in my chain, I'm thinking I'm going to try the "Octavia at the end" mentioned.

Also, shortly after I posted I realized I didn't provide a link to the schems, and my computer locked up as I was typing a follow-up to provide the links.  I couldn't remember what it was I'd been doing once I'd re-booted so they never made it here. Apologies! :-)

[El Heisenberg]

Consider the green ringer with the switchable filter mod. You could add that in front or after the BMP in the same box with another stomp switch. Have you tried the GR with a big muff?

[johnadon]

This has been an interesting exercise. I decided to build another Big Muff from scratch with each stage modular, e.g. in/out leads from each stage. I also put the input through octave stages of the Foxx Tone Machine on the same board. I had great fun patching them together in different orders. In the end, though, I ended up inserting the Foxx portion at the input to the Muff Sustain pot lead, true-bypassable. I also left the octave switchable as it is on the Tone Machine but had to use some extra lugs on the octave side to decrease the resistance between the collector and ground of Q1 on the Big Muff to keep it from compressing the attack to inaudibility. (I don't know what the technical term for that is, but I know there is one.) When the octave switch is not engaged I don't need the reduced resistance there. Once again I have no idea why, but I'm happy to have found a way to make it work.

I originally left the Foxx Sustain pot out, essentially setting it at max, but discovered that you could achieve slightly different tones with it in the circuit even though it was just after the input/sustain portion of the Big Muff. Since I have two sustain knobs that go up to eleven, that makes a total of 22. :-D The second sustain isn't that dramatic an addition, but it was worth the few dollars I put into the pot.

And of course I put in about a million other switches to do neat things that I'll never touch again, including a really ugly octave down that scares my cats (it oscillates at a very low frequency with that switched in though). :-)

Strangely, this build is quieter than my original Big Muff build even when the Tone Machine snippet is patched in. This is especially surprising considering my board looks like a ball of stiff yarn with all the wires going everywhere.

I patched a few other of my boards into different stages including the Green Ringer and they were all pretty awesome. The Big Muff lends itself really well to experimentation since the stages are easy to separate. I really appreciate all the suggestions!!! .

[El Heisenberg]

if it wouldnt be too much trouble, how about opening up the paint program and pasting together a rough schem?

[kristopher612]

here is a fuzz i built up and posted a couple days ago. it has the octave portion of the FTM, which i modded slightly, in a true bypass DPDT stich before a beebaa type fuzz.  just copy the components inside the switch and put that in front of your BMP.  It works better with a clean signal going in since it has less harmonic content to deal with, giving a better octave IMHO.

[Processaurus]

I noticed you omitted the notch filter in the feedback loop from Q2 to Q1, have you tried it both ways, and if so do you remember the difference in sound?  I suspect the notch filter in a negative feedback loop makes a mid boost filter, which probably is where the Foxx gets its reputation for one of the more present FWR octaves.

[kristopher612]

never tried it with the notch filter.  I tried it without, and the octave was so clear that i felt it was unnecessary.  It you match the resistors, caps and diodes from Q2 up to where they join up at D1/D2 and the 100K resistor, it is a great octave.  I didn't have to follow the usual caveat of rolling down the guitar tone knob as long as i played close to the neck.  also i just noticed that I forgot the 2 100K resistors coming off the 10uF caps to ground.  Those were included in my build.  I was in a hurry the first time i posted the scheme, and didn't realize i had forgotten those 2 resistors.

[johnadon]

I tried the Foxx Tone Machine snippet in front of the entire circuit, but found the octave to be more pronounced after the big muff input/sustain stage - but only after I lowered the resistance to ground of the base on Q1. (I think it was the base - I'll need to look at it again and it should be easy to spot because I made it switchable on an extra set of lugs on the octave switch.) I get a really good octave all the way down to the 5th to 6th fret or so. I'm not well-versed enough to know why that is, but I imagine I was bringing the Big Muff gain down to about what the normal input level for the Tone Machine is - which is kind of dumb now that I think about it. It's like having two transistors to keep the input at at the same level. That reasoning falls apart though after considering the (Big Muff) sustain control still lets out a huge amount of gain when maxed out going into the Foxx Tone Machine snippet even with the lower resistance from base to ground. I wish I knew more about this stuff. :-( I'll try to copy and paste together a pic of what I did this evening if I have a chance.

What you say about getting the clean signal with less harmonic content going into the octave circuit makes WAY more sense, but it worked better the opposite way for me. I fiddled with the circuit so much that it's possible I changed some cap values to roll off a whole bunch of upper harmonic content going into the octave up portion. I don't recall doing this though. I can't wait to look at it again to find out how many ways in which my memory has failed me as I typed this. :-)

[johnadon]

I'm so awful with graphics and I couldn't even label the sections when I got to the end of the editing, e.g. Big Muff input/sustain followed by Foxx Tone Machine input/octave/sustain followed by Big Muff first clipping stage. Totally primitive image, but hopefully the circuit snippets are recognizable. I don't know if this is a bad thing, but I copied and pasted the portions from generalguitargadgets.com. If this is allowable I want to credit them. If not I'll take this out immediately.



No idea if I'm posting the image right either. :-)

[kristopher612]

it makes sense that it would be more pronounced after the BMP input stage.  it's boosting the clean volume going into the FTM octave section.  if it works, then go for it.  you might try the values i used in my build if you haven't yet.  they worked well for me , but this may be better in this particular circuit.