Modding a Danelectro Fab Tone

[lethargytartare]

Been away a while, but got on a building/modding kick recently, so trying to document anything that isn't already well-traveled territory -- hence this Fab Tone.  I've had a few of these over the years and still have one that I use regularly, but always want to have SOME way to dial the fuzz down.  I decided to mod it and looked around only to find bits and pieces of things people have done to make it more generally usable.  So I figured I'd document the three things I plan to do:

1. R14 -- that seems to be the first choice for taming it.  One guy put a diode there, but another comment I found interesting was from a guy who put a 500k pot in there.  Having the ability to go from near-zero resistance to higher resistance seems the most potential fun, so that's my plan there.
2. C5 -- the prevailing advice is to yank it to eliminate the mid scoop.  I tried to trace the board and can't tell if you have to jumper it or can just pull it.  Comments seem to say either, so my current plan is to use a switch to jump it or leave it in effect.  So that should be an easy way to keep the stock option (which, personally, I don't mind) and have the mod option...an spst, and wired to the trace side, done.
3. The diodes.  Here's my plan:  I'm going to run wires to a small board with a pair of sockets in the spare battery space (everything is going to go there, actually) so I can swap in different diodes, LEDs or omit them entirely.  I'm really not sure how long it would take me to pick a setup I like enough to solder it all properly, and the range of options make it too enticing to leave that as an open tinkering option, so that's my plan there. 

The nice thing is that the metal Fab has a ton of free space inside, so there really won't be much of a challenge in getting things to fit.

If anyone has any suggestions or cautions, I'd welcome the input.  I'll post pics and try to get sound samples up.

Cheers all!

[lethargytartare]

Wiring done.  Honestly, this is a really simple set of mods, a switch, a pot, and 2 sockets and some vero, and then whatever diodes you want to use.  Pics tomorrow, and I'll try to do some sound clips.  The nice part is that these mods let you keep the pedal in its original config -- put the stock-correct diodes in, switch on the cap, set the new gain knob to roughly 470o and you're stock.  Then you can tinker with the gain and mid, and experiment with diode combos, (or omit them entirely).  Fun stuff.  I definitely see more uses for this with the gain and fab dialed all the way down.  Amazing there's still a lot of drive to it with the gain (2k) and fab all the way down.  I'll probably give it one try with the new pot path open entirely.  Oh and with the gain and fab all the way UP, it's ridiculous -- too noisy to be useful, but also kinda nutty -- notes sustain forever, starts getting octavey-squelchy...and loud.  So, having that in the bag is kinda fun.

[lethargytartare]

(open images in a new tab to see full size)

The spare battery space:


Boards removed:


The components that will be changed.  Note, the three greenies in a row are numbered, from inside to out, C4, C6, C5.  It's odd, but well marked on the board.  So if you do this mod, don't accidentally jumper C6, which is where you'd expect C5 to be:


Board with wires and controls in place:

[lethargytartare]

Testing went well, everything sounds good.  I'll get everything back into the chassis, and will probably test a couple of larger pots before mounting that and calling it a day.  I'm also going to make the outside with a clear indicator where the 470ohm position is so that I can easily bounce back and forth between the changes and the original configuration for future reference.

I haven't dug into the circuit enough to know if a better solution would have been to simply remove R14 and put in a much larger value pot in the Fab spot.  The way I have it now, I think it's like two pots in series that both impact the gain, and that seems inefficient.  I have to go look at the schematic...

[lethargytartare]

The finished pedal.  I called the switch a "mid boost" so up is on even though it's actually bypassing a cap.  But it keeps the toggle away from the knob and it more likely to be in the on position most of the time (I like having the mids back).  The colored stickers are red for max (which is min resistance and max distortion) blue for min (10k resistance), and the yellow is roughly at the 470ohm mark, the stock amount of resistance.  I started with a 2k pot, and that was fine.  I tried the 500k and it was unusable -- 95% of the pot's travel had no impact and everything happened in a tiny slice at the end.  I settled on 10k -- I just wanted to make sure I had the most practical resistance...I guessed 10k would be fine, and it seems to work out well.



Here, in the battery compartment, you can see everything in the spare battery slot.  I haven't done any testing with other diodes yet.

[aron]

Nice Job

[jez79]

amazing tutoral pics, great!
hope it sounds amazing! I will incorporate your ideas into the fabtone I am working on, cheers!

[lethargytartare]

Quick addendum:

I tried a few diodes, no real surprises:

- I put the 4148s back in, tested, yep, just like stock. 
- I put in germaniums, and the output was significantly lower, but the tone was very nice -- definitely better.  Plenty of volume available -- I had to have the volume at 3-4 o'clock for it to be a comfortably over unity, whereas with the other options the equivalent output was probably around 1 o'clock.  If anyone else does this, it's worth trying that option for a while...it was nice.
- Then I tried a few varieties of LED combinations, all 5mm (in my pics above the leds are 3mm), red+yellow, red+green, red+blue...I  liked the LEDs best -- nice tone, good output.  Did the colors matter?  I think so, but not so much that I could (a) pick one over the others, or (b) know if I was actually hearing a difference, or just wanted to. 
- 4001s didn't fit my sockets, so I didn't try that setup...and I was done experimenting, so I let it go at that.

So I stopped at red and blue 5mm leds. 

Oh, and I'm not sure I mentioned it, but dialing both gains up to max is not fun crazy, it's just unusably noisy.  So don't get your hopes up that there's a cool craziness up there.  Which, I guess, suggests that a better option than a pot would be a toggle with a couple of resistances that give you the options you like -- e.g. I could see the stock value, a very high value, and one somewhere in the middle somewhere (with an on-off-on).

Ok, and now I'm thinking about that wealth of space in the battery compartment -- if you did a smaller toggle for the mid-cap short, and a toggle for the gain resistor (instead of a pot), you could surely fit a toggle in there that lets you swap the diodes -- germanium, led and stock...could you get 4001s on there too...a 3p4t rotary (and then you're back to a pot-sized thing in there)...pretty dang cool! 

[supertulli]

Hi everyone. Picking up the suggestion, here goes my build of the mod. Added three switches, the midEq switch jumpers C5; the gain switch sets at R14 a 18k resistor in the Low (off) position, and series that with 6.8k at mid and 1k at hi positions respectively. The clip switch selects between LED, stock 1N4148 Si diodes and 1N60 Ge diodes.

Really worth doing all the mods as they are really simple and the case offers plenty of space for all three switches, or even more if you choose to tweak further. And the pot is IMO a tad to much as the fab and gain pot would overlap easily. The setting I chose gave me 3 ranges with marginal overlap by the fab pot, that is, the mid gain lowest fab would pick up just before the maxed fab in the low gain; and similarly for hi and mid gains.

If you take all combinations and the small overlapping of any two switch combinations, it's like turning a pedal into 18 (all different) pedals! 

Thanks to lethargythartare for posting the very nice instructions.

Cheers