DOD FX53 vs FX55B

Fancy Lime · September 25, 2019, 08:04:42 AM

Hi folks,

I've been looking at some old DOD schematics and realized that the FX53 Classic Tube and FX55B Supra Distortion are pretty much identical apart from some rather minor changes to component values. Schematics:

http://www.americaspedal.net/fx55b/fx55bschem.jpg

http://schems.com/Schematics/Distortion%20Boost%20and%20Overdrive/DOD%20FX53.gif

The FX55B one is the official, the FX53 seems to not have an official schematic so that one may or may not be 100% correct. The diodes to ground may in fact not be there in the FX53. Does anyone know? Or is that indeed almost the same thing just rebranded for marketing reasons?

The pcb seems to be the same and the FX52 Classic Fuzz and FX50B Overdrive Plus seem to also share it. I really like the sound on all of these, although they seem to get little love in general, for some reason. I love the flexibility and simplicity of the topology. Very illustrative in terms of the differences between overdrive, distortion and fuzz. Or lack thereof...

Cheers,
Andy

bloxstompboxes · September 25, 2019, 08:56:01 AM

I made my own layout of this a few years ago and included the differences between DOD pedals that use the same basic circuit with different values.

https://www.diystompboxes.com/smfforum/index.php?topic=112861.msg1043522#msg1043522

Fancy Lime · September 25, 2019, 09:18:00 AM

Nice! Thanks, Eric!

Andy

bool · September 25, 2019, 09:53:24 AM

You could most likely trim down this topology to a one dual-opamp/single-chip schematic.

thetragichero · September 25, 2019, 10:23:46 AM

dod did this A LOT, using the sane pcb doneness for 3 or 4 pedals. tho me that smacks of since pretty ingenious thinking on their part. i happen to love everything about dod pedals besides the fact that any one I've ever had had been funky with the led: if it's plugged in, led is on just low. brighter when effect is on, but drove me mad for awhile

bloxstompboxes · September 25, 2019, 01:29:42 PM

Looking back, I may have mislabeled a component or two. For example, C10 on the layout looks to be C14 in the parts list on FX53. Easy to figure out though, methinks. Let me know if anything needs clearing up.

bloxstompboxes · September 25, 2019, 01:31:38 PM

Quote from: bool on September 25, 2019, 09:53:24 AM
You could most likely trim down this topology to a one dual-opamp/single-chip schematic.

I suppose the input and output buffers could be left out, or even replaced with simpler transistor buffers. I was trying to stay true to the original, minus the switching, of course.

bool · September 25, 2019, 03:39:28 PM

Looking at the circuit I don't think that any of both buffers would add anything to the tone. So if purist true-bypass; these should be left out ... and after that back to the usual "upgrades"; opamp rolling and diode rolling etc.

Rob Strand · September 26, 2019, 06:13:41 AM

Those model look OK but in general DOD factory schematics contain a lot of bugs. The later versions of the pedals don't fix the bugs either they just have different bugs. Crazy stuff.

bloxstompboxes · September 26, 2019, 01:46:28 PM

Quote from: Rob Strand on September 26, 2019, 06:13:41 AM
Those model look OK but in general DOD factory schematics contain a lot of bugs. The later versions of the pedals don't fix the bugs either they just have different bugs. Crazy stuff.

I know. I tried to build an fx60 chorus pedal years ago and found at least 3 different schematics, I think. Built two different layouts and even tried to verify against a working original but I missed something. Haven't had the time to reverse engineer the thing for my own schematic.

Rob Strand · September 26, 2019, 06:25:46 PM

QuoteI know. I tried to build an fx60 chorus pedal years ago and found at least 3 different schematics, I think. Built two different layouts and even tried to verify against a working original but I missed something. Haven't had the time to reverse engineer the thing for my own schematic.

Usually (with some effort) you can see the circuit won't work but fixing it *and* being faithful to the original is a little tricky. In a few cases I've found pics of the PCB and re-traced the areas that look dodgy.

Fancy Lime · September 27, 2019, 05:44:29 AM

Quote from: Rob Strand on September 26, 2019, 06:13:41 AM
Those model look OK but in general DOD factory schematics contain a lot of bugs. The later versions of the pedals don't fix the bugs either they just have different bugs. Crazy stuff.

Hmm, that might explain the 3.9M feedback resistor in the gain stage. Seems an odd choice when combined with a 500k to ground gain pot. Oddly narrow gain range.

Andy

Fancy Lime · September 27, 2019, 05:57:49 AM

Quote from: bool on September 25, 2019, 03:39:28 PM
Looking at the circuit I don't think that any of both buffers would add anything to the tone. So if purist true-bypass; these should be left out ... and after that back to the usual "upgrades"; opamp rolling and diode rolling etc.

I actually like the DOD buffer and bypass system for it's simplicity. It does not have the best rep, though. I have seen it called unreliable. I am wondering if that has to do with the electronic switching or the mechanical actuator. If the electronics are reliable, that may make a good daughter board for switching that can directly replace true bypass switches.

BTW, what is "diode rolling"?

Cheers,
Andy

News:

DOD FX53 vs FX55B