Foxx - Tone Machine  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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trjones1
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Post by trjones1 »

I'm surprised there's not more on this pedal. IMHO, this is the best fuzz/octave circuit out there. I'll add my layout. It's a pretty tight, compact design using board mounted pots and miniature 10uf electrolytics in order to pack it into a board that will fit mounted the long way in a 1590BB. You could probably even stuff it into a B size box if you're ambitious. The asymmetrical layout and wonky position of Q1 were necessary evils because of the board mounted pots and size limitations, but I've built a couple of these from this layout and they sound great.

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This is my completed build:

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If anyone builds from this layout, let me know how it goes.

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Post by mictester »

:applause: Nice build, but your board is very cramped! I've built dozens of these - no two quite the same - and I did a small PCB layout for it, which included the pots. I got the board to look good as well - all the transistors are in a nice row, and the resistors and capacitors line up too.

No two of them were ever quite the same, because the players who bought them often wanted slight changes, including a clean boost output option, changed tone circuit, more drive and so on.

It's well worth experimenting with values in the tone circuit, in the preamp stage (to give more drive), and in the distortion stage. The guys at Foxx had done a really good job of getting the values right, but it's really open to modification!

If anyone's interested, I'll post my PCB layout (when I can recover it from an old hard drive!).
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Post by Crumbchildz »

Changing or removing the clipping diodes has a (obviously) dramatic impact on the sound. And I totally agree with Mictester, no two of these ever sound the same. Some are huge and ballsy, some thin and metallic. Either way, they're always usable. :wink:
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Alex Frias
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Post by Alex Frias »

I built one using the same components described on GGG and it sounded great, very like what I know as it must sound.

On the other hand I made another one including some mods an addons to match some goodies on Prescription Electronics Experience and Fulltone Ultimate Octave. This unit is what lives in my pedalboard at this moment.

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Chrome Dinette
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Post by Chrome Dinette »

These are great pedals, but I like mine better after a couple of changes. I have one of the reissues that I picked up cheap, used.

I put a dc jack and led on it, for starters. I used a smaller cap at the input to the first gain stage. I also replaced the first transistor with a Russian MP10a. Now the pedal is a little less flabby on the bottom end and the gain is more manageable, for me.

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Post by RnFR »

what's up with the mp10a? is it Ge? npn?

i like the nfb between Q1 and Q2. you can get some nice tonal shaping this way. compare it to the fuzz face and you can see the difference.
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Chrome Dinette
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Post by Chrome Dinette »

The mp10a is npn ge. I bought a bunch of them on ebay for cheap.

I have used similar feedback sections in some home made 3 transistor fuzzes, with switchable caps to adjust the tone.

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Post by Thaxt »

Looking over the insides of my Foxx Tone Machine (purchased used in 1983) I see that this one has (2) 270pf caps shunting to ground in 2 places - presume this is to tame that octave screech & overall treble a bit more. I wonder if this was a latter day addition by Ridinger?

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Post by ringworm »

I've been trying to do so some research and make up a layout for this but have come across an anomaly with the known schematics (GGG and FuzzCentral). Both of these schematics show only 21 on-board resistors (excluding pulldown and led resistors) but having checked out some gut-shots there are 22 on-board resistors.
FOXX_TONE_MACHINE_GUTS.jpg
I have marked the extra resistor (10k) with a yellow 'X'
You can see it is not included in the gut-shot of this Paraclete Fuzz Sustain.
P1030801_800.jpg
But here it is again in another Tone Machine shot.
IMG_0816.JPG
It appears to be connected to the 'sustain' pot.
The top gutshot has 3 x 10k resistors while the circulating schematics only show 1. I'm presuming that one of the 10k is a replacement for a 15k.
Could anyone provide a trace side shot of an original pcb for verification of this extra part? Or does anyone have any idea what it does (if anything)?

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Thaxt
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Post by Thaxt »

Changing the diodes does indeed produce dramatic results w this pedal.

Try LEDs, 1N4001s, 1N4148s, 1N914s, FETs as clippers, et al. And the AMZ "warp" mods make great adjunt possibilities with the diode changes

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Post by Dr Tony Balls »

Not that there arent a number of great layouts already, but here's one I just whipped up. It satisfies my own personal OCD to have the resistors lying down and most of the caps appropriately spaced. Its also a bit bigger than the standard layout for those of us that build big boxes.

farm8.staticflickr.com/7091/7302952724_51075cd25f.jpg

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ringworm
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Post by ringworm »

An attempt to clone the original layout. Has optional parts that where included/absent from the original and it's OEM brothers and sisters. Let me know if you spot any errors. Enjoy.
foxx.pdf
(213.23 KiB) Downloaded 440 times

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IvIark
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Post by IvIark »

Forgot to add this, but may as well now for a bit of variety. This one is verified and should fit in a 1590B easily enough.

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Post by DesertCruiser »

Hey, I just came up with a cool and really simple mod (bet somebody already done it) that let's you enable a "super gain" mode when the octave is disabled.
You just switch the loose end of the cap at the emitter of the 2nd trannie down to eart to let it act like a bypass capacitor instead whitch will increase the gain of the 2nd trannie.
I guess this disables the tone shaping feedback loop from the 2nd to the 1st transistor as well, which would increase the gain even more.

This is easily done by changing the ON-OFF octave-switch to a three mode ON-OFF-ON switch and connect the middle pin to the "emitter cap" and one of the other pins to the diode's cathode. Now the signal connection is broken between the diode and the cap instead of between the diode and the resistor, works just as good.
Now to the good part, just connect the third pin of the switch to ground and you got yourself a Tone Machine with three modes instead of two. Simple.

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This third mode has got crazy/unusable amounts of gain which maybe can be good for solos and stuff..
I breadboarded it and it's really noisy so you may want to roll back the gain or the volume on the guitar a bit when in use.
Could be a good idea to just rewire the oiginal switch and add a "super gain" footswich instead to be able to turn it on and off fast when you're giggin.

What do you think? :)

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Post by cortezthekiller »

ringworm wrote:An attempt to clone the original layout. Has optional parts that where included/absent from the original and it's OEM brothers and sisters. Let me know if you spot any errors. Enjoy.
foxx.pdf

This is an excellent replica file, though I noticed one difference between it and other schematics of the tone machine:
C12 is specified as 0.03uF in this version, whereas other schematics show it as 0.003uF. This affects the high end of the tone
control and is the only difference/error I've found.

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ringworm
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Post by ringworm »

Good catch! The 0.03uf was listed on the schematic (the one I worked the project up from) but I see 0.003uf everywhere else. I never got round to actually building this up, so wouldn't have spotted the mistake. :oops:

Update below:
foxx.pdf
(220.67 KiB) Downloaded 371 times

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The Rotagilla
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Post by The Rotagilla »

Hey guys,

I just built out a Tone Machine and there seems to be excess noise and I'm also picking up radio signals. I happen to have a Fulltone Ultimate Octave here as well and it's much quieter than my build. I've implemented most of the UO mods (left off the Bright/Fat switch) which brought down the noise floor a little but I'd like to get rid of the radio interference. Any suggestions would be greatly appreciated, thanks.
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mictester
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Post by mictester »

Try 47p (approx) capacitors from base to emitter of the first two transistors. Don't worry too much about the actual values (but don't make them too big or you'll lose treble).
"Why is it humming?" "Because it doesn't know the words!"

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Post by astrobass »

How are you filtering your power supply?
What does your wiring look like?
Is it in an enclosure?

Show some pictures. Odds are you're either not doing as much filtering on the power supply as they are, or your work isn't as tidy. Sloppy wiring WILL give you a noisier pedal.

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