foxx tone machine... how do i get the octave up a little louder?

[pinkjimiphoton]

built one of these


and i love it. really nice useful fuzz, and the octave is pretty freekin sublime.

but using it last nite live for the first time, i noticed that the octave was really weak compared to the fuzz... i realize it can't have the ass of the fuzz, but it needs just a hair more.

did the standard neck/tone almost off/12th fret thing, its octaving beautifully, but it just seems like it should be louder.

interestingly, kicking on my univibe made it stand out a lot better.

my question i guess is, if i were to add a pair of bypass caps to the e resistors at the second and final stage, and maybe reduce the 4k7 resistor to ground with a 2.7k-3.3k resistor at stage 2 <or even use a 4pdt footswitch to switch the octave in and out instead of the 3pdt i'm using just 2 poles of now> would that raise the volume up sufficiently do you think?

i saw marks suggestions about changing the second set of diodes, but i really dig the tone as it is, just need a ...ummm...RCH as we used to say more testicular fortitude.

i thought the bypass caps, maybe 2.2uf to 10uF may give a bit more balls,
and then was thinking that if i switched that resistor on the second stage in and out when the diodes are connected it might give that little bit of extra "oomph" it seems like it needs.

the bypass caps not my idea of course, i found it researching an old ampage archive post... but they suggested it on the final 1.5k e stage. i was curious if it may work on the second stage as well.

any ideas/advice are gratefully appreciated. just wanna dial this puppy in just a little better. i use a fuzzface for my fuzz, so most of the time, all i will use is the octave up side of this.

thanks peeps. peace!

[highwater]

my question i guess is, if i were to add a pair of bypass caps to the e resistors at the second and final stage, and maybe reduce the 4k7 resistor to ground with a 2.7k-3.3k resistor at stage 2 <or even use a 4pdt footswitch to switch the octave in and out instead of the 3pdt i'm using just 2 poles of now> would that raise the volume up sufficiently do you think?

the bypass caps not my idea of course, i found it researching an old ampage archive post... but they suggested it on the final 1.5k e stage. i was curious if it may work on the second stage as well.

The second stage is the phase splitter. Any mismatch in the resistors will reduce the octave effect, and a bypass cap would probably eliminate it entirely... but both might be fun to play-around with the next time you want to build another non-octave fuzz.

Easiest thing to try is the Ampage suggestion; no soldering needed, just 'gator clip a big honking cap across the 1k5 on Q4. If that gets the octave setting loud-enough, you can switch that, the diode, and an indicator with the 3PDT. You'd have to be careful about how you switch the cap, or popping could be an issue... but that's above my pay-grade, and anyway it's not worth being clever about it until you know it'll do what you want.

[JustinFun]

I found sticking a hogs foot in front of it really boosts the octave.

https://www.diystompboxes.com/smfforum/index.php?topic=113064.0

I built one where i put a switchable hogs foot in the box - you can even get a decent octave on the bridge pickup and with the fuzz rolled back.

Definitely underrated as an octave fuzz - much better than the superfuzz for me, which I've never got on with (although maybe I'm just doing something wrong as everyone else seems to love them)

[Mark Hammer]

I may be misunderstanding your post, but the diodes to use Schottky with instead of Ge or Si is the pair coming off Q2, and NOT the back-to-back pair going to ground.  This allows more signal to pass without chopping off the nose and tail of notes.  Some folks might prefer the semi-gated sound of Si in that position.  Personally, I prefer the smoothness of the Schottky.  It also makes for less of a grainy fuzz when the octave is turned off.  On the other hand, the crossover distortion produced by forcing the entire signal to pass through one diode with a higher forward voltage may be something a person likes.  The ideal is probably to switch between the two Schottky types when octaving, and no diode when the octave is defeated.

I think the diode pair to ground, found in a number of commercial octave-up units. tends to be misunderstood.  Often mis-interpreted as the basis for the fuzz, you'll find if you lift that ground connection, you still get plenty of fuzz.  What you will lose, however, is the clamp on level they provide. 

That ersatz limiting effect is important.  Remember that picking a string unleashes all the harmonic content at the outset, which all gets doubled by the circuit.  The octave gets lost in the doubling of all those harmonics.  The string is also slightly deformed, with a teensy bit of pitch bend, making the octave harder to hear at the outset.  The circuit doesn't "know" how to identify the fundamental; it just doubles whatever it gets that can pass through that first pair of diodes.  As the note sustains, the harmonic content fades away, and the overall level subsides to focus on the note fundamental. 

Veteran users of octave-up units will know that the trick to getting pleasing octaving is to a) use the neck pickup, b) fret above the 7th fret, and c) roll the tone back on the guitar.  All of that emphasizes the fundamental and downplays the harmonics. 'B' is important because the shorter the string length, the less compliant it is, and the less harmonic content.

By holding the level fairly constant, via that 2nd diode pair going to ground, one allows the octave to "bloom", by coming out from under the flurry and haze of doubled harmonics, without the progressive loss of level that would occur if the diodes weren't there.  In other words, killing the dynamics helps in this instance.

However, the price one pays for doing this is that the diode pair to ground introduces a bit of its own clipping; especially if you use Ge diodes in that location.  Dino suggests inserting a small-ish value of fixed resistor (e.g., 470R-1k) between that second diode pair, and ground, to soften any clipping they introduce, while keeping as much of the limiting effect as possible.  I'll suggest also putting a small-ish value cap (e.g., 1000pf)  in parallel with that diode-pair-plus-resistor, to further trim back on any doubled harmonics that still remain.  A person may want to dicker with the tone control as well, but I'll leave that to them.

I find that with Schottky diodes for the first pair, I can get clearly audible octaving down to the 5th fret, and even a bit lower on the unwound strings.  If I were to use flatwounds, I suspect I could get it below the 5th on the wound strings as well.

All in all, it's not a matter of making the octave louder, but of making the doubled content you don't want softer/quieter, so that the octave is more noticeable.

[pinkjimiphoton]

thanks for the suggestions guys, i'll rip it off my board tonite after the gig.

the two things i noticed the other nite the first time i used it, were that the overall pedal needs to be a bit louder,
but the octave is around only 70% of the percieved volume of the fuzz.

if memory serves, i used either 1n34's in it all around, or 914's. the guy's bloody site keeps going down everytime i try to look up the bom. ridiculous. probably one or the other.

don't really have room to add another board to the pedal , not to add another pedal to my board at this point. i suppose i can live with it, just a drag to have to tap dance on the univibe on the other side of the board every time i use it, but man, it sounds great together.

i'll try some shotkes and see if it helps. will make it track more like gus's ousb it sounds like, but i hope it doesn't harsh the tone too much... the ousb is the best tracking of all the octave ups i've messed with, but there's so much filth for me its just unuseable unfortunately.

i agree that the diode pair to ground is to limit it or add a bit of compression. i got yelled at on one of my projects for including a switch to choose diodes like that or not. they were strictly just to add a little squish at the end to keep volume levels more constant, but because the switch "didn't do anything" <smh> the guy was all upset. he thought compression meant compressOR. <smh> in later builds i left the switch out and the clipper on, tho it limited some of the stuff you could do with it.

so.... shotkes for the first diode pair, bat41's i think i have in my bin still from years ago. check.

add a small resistance between the second diode pair, ala jack orman's warp controls. check. i'll lift the ground end, and try a 2k -4.7k trimmer and dial it in. check. will try a smallish cap there too to smooth it over. but i love the way it sounds now, just need more on the octave.

i'll at least try the final stage bypass cap and see if it gives a bit more juice, too. thanks guys!!!

as usual gig tonite so it'll be a couple days before i can get to this, but i appreciate the advice.

rock on!! and stay tuned

i just realized my router was off for some reason and checked the bom... all in34a, probably where the volume issue is coming from?

>>>fOXX Tone Machine<<<

This is replica of original Foxx Tone Machine guitar effects unit came out in 1971 and was
made for only a few years, but its fat-backed, fuzzed-out sound has made it a coveted piece
ever since. It has been a favorite of such guitarists. Assembled in the USA, the Tone Machine's
controls include volume, sustain, and and Mellow/Bright fuzz tone knobs, and an octave/sustain
switch.

It is a very nice project with a classic fuzz sound, and a very good octave up effect. The octave
in this pedal is more pronounced than in the Tycobrahe Octavia.

Resistors 
Resistor part numbers are for 5%, 1/4-watt carbon film resistors 
1 - 4M7
1 - 470K
1 - 150K
5 - 100K
3 - 47K
1 - 22K
2 - 15K
1 - 10K
3 - 4K7
1 - 1K5
2 - 1K
1 - 220 ohm

Potentiometers 
3 - 50K taper pot (16mm)
(2x Lin 50K for Sustain/Tone & 1x Log 50K for Volume)

Capacitors 
8 - 10uF Electrolytic
2 - 0.1uF Orange Drop
1 - 0.05uF Orange Drop
1 - 0.003uF Orange Drop
1 - 0.001uF Orange Drop

Transistors 
4 - 2N3904 (originally 2N3565)

Diodes 
4 - 1N34A Germanium diodes
1 - Red super-bright LED, water clear lens

Other Parts
1 - Hammond 1590BB aluminum enclosure
1 - Switchcraft enclosed stereo input jack
1 - Switchcraft enclosed mono output jack
1 - 3PDT Stomp Switch
1 - DC Power Jack with N/C Switch, Plastic body
1 - 24 gauge white stranded hook-up wire
2 - Black plastic knobs, 1.04" dia.
1 - Black plastic knobs, .75" dia.
1 - LED mounting clip, 2-piece
1 - SPST miniature toggle switch

highwater, a good rule of thumb i've found for reducing noise is to have the ground connection with switching connected to ground, and then use the switch to ground whatever. tends to be the least noise. if ya do it the other way, the item connected to the switch, and then the switch to ground <with the switching of the switch pole to ground, i mean> ya get more pop.