Hot-Rodding an OD-3 kit

[Cozybuilder]

An E-Bay seller has been marketing various pedal kits, among them a modified "Boss OD-3" kit. This is available in 3 options: with a painted & predrilled box ($19.99), a painted but undrilled box ($17.99), or with a plain box ($14.99), delivered. The price seems reasonable, but is it worth it? Some would say no, others think it is. I already built the painted & drilled box kit, as reported in this thread:
     "Has anyone built the DIY kits from the seller protaitone on ebay ?"

This project builds on the lessons learned from that experience. If you choose to build this kit, read the other write-up for additional information not repeated here.

That pedal sounded good, fit the box (after moving the I/O jacks a bit), but I felt it could be improved on. So back to the breadboard; the first objective was to improve the circuit sound. This was done by changing the electro and ceramic caps in the signal path to polyester, the ground caps to either MLCC or Tantalum, and some of the component values were changed (details are provided below on the schematic). In fact, all of the kit capacitors were changed. Once satisfied with the circuit sound, the next step was to try out some mods. An internet search showed that Keeley developed 3 mods a few years ago for the Boss OD-3. Each was tested, gives a different voice to the pedal, and sounded good, so I incorporated each of them. These were put on switches, arranged to give the most variety for the least amount of real estate. This includes the original OD-3 circuit, so you don't lose the original pedal sound by modding it. On other forums that was a concern a few years ago.

In the end the pedal is capable of delivering sounds from clean boost at one extreme, to high gain fuzz at the other, with a huge volume boost. The tone control works very well. This project has evolved from a good pedal made from a $20 kit, to a great pedal from a $15 kit. So, with all this info I decided to show what could be done with a cheap pedal kit from China, and how to do it.

Here is the modded circuit:                                                                                    And the kit as delivered:

 

These are the parts I recommend replacing:





Note the extra holes drilled in the PCB shots- these are needed for replacing EC3 and EC6 1uF aluminum electro with Wima 50V 1uF polypropylene caps; EC4 with a 1uF MLCC (you can sub a 2.5mm lead spacing ceramic here without drilling); the D3 and D4 diode leads are relocated into the space occupied by EC2; EC2 is relocated to share holes with R9 and R10; 2 holes to add a reverse polarity protection diode above R2; and 6 additional holes for the leads to the mods (All holes are in the populated cards). Notice that none of these holes damages a PCB trace.

The leads to replaced parts and mods are wired as follows:
  EC3: this is located as shown so that the hole in the board can be used for a standoff if desired. Referring to the EC3 designations, the +side is hard-wired to top of R12, the - side to bottom of R11.
  EC6: Using the EC6 designations, the +side is hard-wired to R25, and the - side to C6. Also note that the EC6-C6 junction is used for a lead for the 'Dirty Boost' mod, crossing under R26 on the trace side; the other lead is connected to R20 for this mod. Look closely at the photos above for the hole locations.
  EC4: The lead is hard-wired to the anode of the nearest unmarked diode. Alternatively you can sub a 1uF ceramic cap with 2.5mm lead spacing.
  EC2: Place R9 and R10 in their holes, and place the +lead of the 10uF Tantalum cap with R9, and -lead with R10- do not solder until these are all in place, and resist the temptation to enlarge the hole- these PCBs have minimal soldering surface to start with.
  Diodes D3 & D4: The holes are located to avoid the traces, and allow enough space to lay the diodes flat. Be sure to use an insulated wire between the diodes so they don't short to the original EC2+ solder point. 2 additional holes are drilled below R14 for the "Clean-Boost" (or "Diode Lift") mod. One lead goes to the diode leads just relocated, the other lead goes to C4.
  The third mod is a "Distortion and Volume Boost". It just requires 2 holes for the leads, one to each end of R17.
  A 1N5817 is placed above R2 for reverse polarity protection.

In addition to improving the sound, the above changes make the board significantly shorter, so that you have more flexibility in placing it in the enclosure. I chose to make a Wedgie, see this thread:
       "Wedgies Anyone? A 1590B tutorial"
for instructions.

This is the toggle switch arrangement I used:                                                                 



The two resistors for mod 3 (schematic, 8K2 and 2K7) are placed on a small daughterboard on the SPDT.



And the $15 kit completed:

[Cozybuilder]

Some of you will have the additional parts, others will have to order. Most of the parts are available from Tayda, the others from Mouser. For some items, there is a minimum order quantity.
Tayda:                                                                                              Mouser:
OD-3#    Amt     SKU        Description                                                OD-3#     Amt      Mouser#                     Description
Vol,Drive $1.00   A-1650   Alpha 16mm 100KAudio Pot (2 ea)              EC3,6      $0.84    505-MK521/50/10       Wima 50VDC Film cap, 5.0mm spacing (2 ea)
R5          $0.12   A-2247   470 ohm resistor (10 ea)                            C4           $0.47    80-R66DD3470AA6AJ  Kemet 63VDC film cap, 7.5mm spacing (1 ea)
Added     $0.12   A-2626   2K7 ohm resistor (10 ea)                            R3           $0.15    270-2.7K-RC               Xicon 1/8W 2K7 ohm resistor (1 ea)   
R11        $0.12   A-2312   3K9 ohm resistor (10 ea)                            R4           $0.15    270-8.2K-RC               Xicon 1/8W 8K2 ohm resistor (1 ea)
R15        $0.12   A-2328   6K8 ohm resistor (10 ea)                             sub-total  $2.54
Added     $0.12   A-2337   8K2 ohm resistor (10 ea)                            shipping   $4.99
R30        $0.12   A-2329   220K ohm resistor (10 ea)                           Total         $7.53
Q3          $0.04   A-228     BC327 PNP transistor (1 ea)
Added     $1.89   A-361     DPDT Latching Footswitch PCB (1 ea)
Added     $0.85   A-5110   DPDT mini toggle on-off-on (1 ea)
Added     $0.47   A-5108   SPDT mini toggle on-off-on (1 ea)
D5, 6      $0.02   A-157     1N4148 switching diode (2 ea)
Added     $0.06   A-159     1N5817 Schottky Diode (1 ea)
C3          $0.03   A-1448   1000pF Monolithic cap (1 ea)
C8          $0.03   A-1366   .01uF Monolithic cap (1 ea)
C12        $0.04   A-1472   .022uF Monolithic cap (1 ea)
C7          $0.04   A-1476   .056uF Monolithic cap (1 ea)
C1          $0.12   A-142     .470uF Monolithic cap (1 ea)
EC4        $0.12   A-321     1uF Monolithic cap (1 ea)
C5          $0.10   A-701     8n2 Poly box cap (1 ea)
C6          $0.09   A-559     10nF Poly box cap (1 ea)
C9          $0.10   A-703     18nF Poly box cap (1 ea)
C11        $0.09   A-561     33nF Poly box cap (1 ea)
C10        $0.10   A-563     47nF Poly box cap (1 ea)
C2          $0.12   A-707     68nF Poly box cap (1 ea)
EC2,5,7  $0.36   A-1472    10uF Tantalum cap (3 ea)
EC1        $0.23   A-633      22uF Tantalum cap (1 ea)
subtotal  $6.62   
shipping  $1.33               
Total        $7.95

As you can see, if you have to order each part needed, it basically doubles the kit cost (I already had everything in my pedal-building supplies). You might also want to upgrade the jacks and knobs, I used Switchcraft I/O jacks, unswitched 9V power jack, and aluminum knobs.

[Derringer]

bookmarking this thread

thanks for the info Cozy!

[duck_arse]

what with all this development work done by cozy (that he shouldn't have needed to do), it will be intersting to see if any changes "appear" on subsequent boards/kits purchased from the geezer. it would be in the sellers best interests, surely.

[mitchschaft]

Do you happen to have a shot of the component side of the daughter board for the switch?

Did you use a .4 bit and 26awg wire for the holes? or .3 and 28awg?

[Cozybuilder]

The hookup wire is teflon coated 26AWG solid core. I use a 0.8mm bit for drilling the PCB (and for pilot holes on the box too).

The mod is just two ¼ Watt resistors mounted on the same side as the SPDT toggle on a small piece of perf- I didn't take a shot of the other side of the daughter board, but heres the wiring diagram:



Remember the toggle lever selects the opposite side pole, so as drawn the lever up selects the 8K2, lever down selects the 2K7.

[mitchschaft]

I just finished putting the switch together. I used stripboard since that's all I have lying around. I'm pretty sure I got it right. Let me know if I didn't:







I have to wait on the drill bit to arrive to finish the rest of your mods. Thanks for giving me the chance to learn. This is awesome. I learned about the switch being opposite last night from looking at datasheets and such.

[Cozybuilder]

Your switch looks OK to me.

[mitchschaft]

Everything in my end is working out so far. Except the dirty boost doesn't give a slight volume increase like you state that it should. It sounds as loud as "normal". Clean boost is definately louder. Any ideas?

[Cozybuilder]

Hi Mitch-
You should be getting a volume boost with the dirty boost option. Please verify that the leads for the switch in your build are as shown in the schematic. Note that I had to revise the component placement on the PCB to accommodate this change.

[mitchschaft]

Instead of moving the D3/D4 leads, I cut the trace that leads to C4. I didn't move the other components since they fit in the hole fine and I wasn't worried about them sitting flat. I can't remember if I changed out R5, R11, R15 and R30, though.
Other than that, it's wired up the same.

/edit
I forgot to swap out those resistors.

[Cozybuilder]

I made a mistake on the list- R15 (1K) is fine, its R13 that needs to be changed to 6K8, look at the schematic. R30 change to 220K is crucial. R5 and R11 will affect the tone.

[mitchschaft]

I had R30 correct. It was R5, R11 and R15 I missed. I swapped them out and it killed the volume. I guess I'll swap R15 back lol.

[mitchschaft]

I call this 'Ode to OD-3'. Not as eloquent as yours, but it's effective.









don't mind the lifted pad repairs at the bottom left:


I didn't use the same caps, kemet and wima, as you. Could that be why I don't get a volume boost in dirty boost mode?




I just need to add the switch labels. The off LED is a bit underwhelming. I should add one to each corner. Thanks for all the tips!

[Cozybuilder]

Hi Mitch-
Thats the first time I've seen someone use the Off LED on one of these kits, and you get bonus points for illuminating a light plate. Good job 

The "Dirty Boost" essentially cuts out a filtering stage, so you should see a volume boost regardless of the type of caps used, unless that filter cap to ground is open (C7, 47nF). Your wiring looks correct, so other than that I'm at a loss as to why you don't see the volume increase. How do the other mods work for you now?

[mitchschaft]

I don't get it either. I've stared at everything for hours. C7 seems fine as far as I can tell. Continuity is there all around it. Unless it's a bad cap. If that's all that's "wrong", then I'm happy. it still changes the sound some. I haven't tried it through another amp, though.

I decided to use that little plate spacer to give me a few more mm's of space instead of drilling the jack holes out. I found them on ebay. They're 3D printed and the guy uses them for his homemade vape machines ha. Plus, I wanted to use the off LED just because it's there.

All the mods work great. I love the switches and I learned a lot from the experience. Not bad for $30 all in. One thing I learned is don't apply too much heat to the switch lug. I killed the 3PDT (that's why I couldn't get clean signal) and the SPDT switch from that. Too bad that other thread got killed.

[AdminoPasswordo]

Hi Cozybuilder,

I know, this is a very old thread, but, believe it or not, it is the only one I could find about the OD-3 Overdrive Clone that I just bought.

Mine came with next to no info on how to build it. I got a BOM and schematics which do not match. While I don't feel confident enough to follow your modding instructions I guess I can pull off the unmodded build.

I am most interested in (1) the polarity of the FETs (the icons on the board seem to be reverse), (2) the wiring of the off board components (I can infer some of the wiring from the schematics but I'd be more confident if I had some confirmation. What do I connect to [on] and [off], is [J] for jumper?) or if you had an old (3) photo of the assembled board. You are mentioning an even older thread "Has anyone built the DIY kits from the seller protaitone on ebay ?", which for the live of me, I can't find. Is it still online?

I know this is a lot to ask, but any help is appreciated.

Cheers,

Andy

[Cozybuilder]

Can you post details on the kit you purchased, such as the schematic, photos of the PCB (front & back), and the parts list?

[Derringer]

I bought one of these kits not long after Cozy made this thread. I finally built the thing a few months ago. Cozy's schems that show the part numbers were indispensable. I perused all his pics relative to this build in photobucket to get the big picture.

I'd definitely recommend breadboarding the circuit before committing to solder ... I did, and that in itself helped me figure out the JFet orientation as well as find which resistor values and higher quality caps I needed to sub from my own parts bin.

[AdminoPasswordo]

Hi guys,

I bought this kit: https://www.aliexpress.com/store/product/DIY-Overdrive-pedal-Guitar-Effect-Pedals-Electric-Effects-BLUE-Suite-OD3-Electric-guitar-effects-pedals/1045809_32324066430.html?spm=2114.12010612.0.0.VAB1mW

The BOM matches the board with the exception that there are only 4 diodes. The schematic seems to be of the unmodified original OD-3.

I traced the PCB and drew the schematic of the board, cross referencing the schematic Cozy supplied above. That helped me understanding the kit much better. The fact that the PCB and BOM differ from the schematic that is shown on the suppliers website seems to be down to the fact, that the circuit has been simplified to reduce the component count.



Thanks for taking the time.

Cheers,

Andy