From Yech to Yeah! - modding a DOD FX53

[Mark Hammer]

I had a significant birthday the other day, and one of my oldest friends gifted me with a box of pedals he had collected over the years.  Some were great, some not so much.  Among the second category, which my friend described as "sucking tone", was a DOD FX53 Classic Tube.  I recall modding one for a friend several years back and not being particularly inspired with it, pre or post mod.  Plugging the new one in, I concurred with my friend's view.  It was neither "classic" nor particularly tube-ish.  So, I took an hour to see if I could improve it.  Here's the schematic.

The circuit is virtually identical to the FX52 Classic Fuzz, except that where the FX53 has both feedback and clipping diodes, the FX52 has just clipping diodes.  I have enough "fuzzes" so I thought I'd try and nudge it more in the diretion of something like and SD-1 or TS-9, albeit with a different tone control.

First thing, I removed the two clipping diodes.  They can be seen in the lower left hand corner of this gutshot, nuzzled up against the LF353.  I like double clipping, but I have the amp to help with that, so one set is enough in the pedal.

The second thing I did was change out the 120pf feedback cap in that clipping stage for 82pf, to raise the rolloff point a bit.  I also dropped the value of the feedback resistor from 3M9 to 1M5.  Max gain was still going to be much hotter than even an SD-1, but would be a bit more dialable.  The treble rolloff would start around 1.3khz, compared to the 340hz of the stock unit.  So, not shrill, but a bit more vocal.

The tone control is an interesting one, but generates far too much "woof" to the left of the midpoint.  It was clear the 10uf cap (C11) was at fault, so I traded that for 220nf.  It still has some girth/body to the signal, but much less woof.  No TS mid-hump, either.

I would not describe these mods as turning it into a collectible.  And I suspect that an hour on the bench may not have been enough time to nail the optimal changes.  But it sounds a helluva lot more interesting, better for bluesy playing, more usable, and cuts through nicely.

These units show up regularly on used gear lists for a song...more than likely because my friend and I aren't the only ones with a dismissive opinion about them.  But they make a nice platform for experimenting, and are worth picking up for that reason IMHO.

[bloxstompboxes]

I made a post somewhere here with a layout and everything if someone wishes to build one. I built mine stock except added an asymmetrical clipping switch in the feedback loop, I think it was.

[Mark Hammer]

I may just stick a small resistance in series with the feedback diodes to soften the clipping a bit.

[bluebunny]

I had a significant birthday the other day

Happy (belated) Birthday Mark!   

[digi2t]

Happy Birthday Mark!! (From one 'ole fart to another  ).

I have just the gift for you...

At the end of the month, I'll be heading to your neck of the woods. How about I bring you this to noodle with for a while?



Then you'll be able to say that you've ACTUALLY SEEN... IN THE FLESH... A BONAFIDE... REAL...

MN3214. 

[Mark Hammer]

Yowza!

I'll be home, Dino.  For that, I'm not moving from the spot.

[Mark Hammer]

Incidentally, a did stick a 6k8 resistor in series with the clipping diodes, and it sounds pretty nice. 

[Mark Hammer]

Nota bene: I misspoke.  The two diodes in the lower left-hand corner of the gutshot are the feedback diodes.  I kept those.  The clipping diodes are the pair in the upper left-hand corner, beside C6.  I reduced C6 from 1500pf to 1000pf, which also helped to open it up a bit.