first time builder, difficult first pedal

[gross_motor]

Hey everybody. First post! Name is Lucas A.

I've never built a pedal before, but I do have a nice soldering setup and have replaced electronics in several guitars, and I did build a small synth project once. I'm confident I could do it with instructions etc. I know what the different components of pedal building are, but that's about the extent of my knowledge. I joined this forum because I have a pedal I want to recreate, the problem is the circuit uses all surface mount components and it seems to be pretty complex. The pedal is a Behringer OD300. It is apparently based on a Boss OS-2, but I purchased an OS-2 and it does not have the same sound. I have played a lot of overdrive pedals and the OD300 has been my favorite for years, so it would be nice to have a high quality one in a solid enclosure.

I took some pics of the board:




I also uploaded the pics to the community schematics thing that may be higher res: https://www.diyschematics.com/schematics/index.php?/category/community

The stock pedal has a pot on top that goes from overdrive to distortion. Pete's pedals in St. Louis swapped that out for a switch for me. I was going to have him try to put it into a boss enclosure but it didn't work out.

I always keep the pedal totally on overdrive. From what I understand there are 2 circuits for OD/dist and the pot blends them. I wouldn't mind having the option to switch to the dist circuit, but I'd be happy if I could just build a pedal with the OD circuit also.

So I can read all the values for the components on the back of the board, which gives me a nice place to start, but I'm not sure what that IC is as it doesnt have any markings on it. I do think it is an opamp of some kind though. I can also read the cap values on the front of the PCB. So the hard part is the actual circuit diagram I guess. Another complication is the pedal has a weird switch to turn it off and on that I'd prefer to replace with a standard footswitch and true bypass (I have a nice buffer at the beginning of my chain).

So I know it's probably a long shot, but if anyone here can look at the pics and understand how to diagram the circuit for either the whole pedal or just the OD circuit, I'd really appreciate it and wouldn't be opposed to giving some kind of compensation if the build worked out. Thanks a lot!

[Govmnt_Lacky]

Welcome Lucas!

The IC is most likely a quad op-amp like a TL074, TL084, LM324, etc. Unfortunately, if the IC does not have the markings then you may need to research the internet to see if someone has identified it OR possibly someone on here knows the answer.

As for the True bypass, it would not be difficult and would in fact get rid of some of the switching components that are on the board making the parts count lower.

As for the trace..... that one may be a DIY thing. If you have the patience you could try yourself. Since the parts are identified on the board (resistors, caps, etc.) then you could give it a go. Otherwise, maybe reach out here and see if someone has already done the leg work and you could go from there.

Good Luck! 

EDIT: Looks like the transistors are either BC846 or J113. And the chip labeled 56K (563) is a 4-resistor bank. It has 4 seperate 56K resistors in one package.

[Kevin Mitchell]

Welcome to the forum!
That IC is likely going to turn out to be a quad opamp - a LM324 or similar would be my first guess.

We can't see what's going on with the traces under those jacks and pots. But a multimeter can 

-Do you have a multimeter? You'll want to reverse engineer it by following the traces and drawing the schematic.
-Using a schematic drawing software like kicad will help. Start by placing all of the opamps and transistors on the page and link them up in a neat fashion until the input meets the output, from there fill in anything you've missed.

You'll want to breadboard your drawing with through-hole parts to verify your work.

[gross_motor]

I do have a nice fluke multimeter I inherited actually. I'm not familiar with everything it can do but I can test continuity with it. I have a breadboard setup on the way along with lots of parts so I'll start plugging away at that and see where I can get.

[Kevin Mitchell]

Good luck!

Try to keep in mind the oddball parts. Here's some info on what I'm seeing and thinking for through-hole alternatives.
-Input jack is switching, that's why it has an extra lead that the output doesn't have. This is likely to disconnect battery when no input is plugged.
-The chip labeled "563" is going to be a resistor array containing 4 56K resistors. Treat it like 4 independent resistors.
-The "846" transistors can likely be any generic NPN. I'd use 2N5088 or 2N3904 on breadboard for those.
-113 is a "J113" n-channel jfet. A through-hole version can be purchased.
-"3V9" is likely going to be a 3.9v dual zener. Use the diode function on your meter to sort on polarity to determine common anode or common cathode.
-"4148" switching diodes can be 1n4148.

As you question parts try to source the datasheets to inspect & verify pinouts. If you get stuck the forum will be happy to help!

[ElectricDruid]

Behringer also made a OD100, and there are mods for the OS-2 that are supposed to work on that too. If I had to guess, I'd say Behringer's first pedal was a direct clone with very few changes (OD100) and then they later did a slightly-more-tweaked one (OD300). Nonetheless, I'd suspect that the OS-2 schematic would be a good place to start if you're tracing it. Yes, you'll probably find differences, but if you find that some of it is the same too, it'll save you a lot of time. Some of the changes might be in component values, rather than actual schematic changes, so that would help too.

I can't find an original Boss schematic for the OS-2 anywhere. I'd recognise the style, and anyway, all the ones I've seen don't have the FET switching on, which the Boss would certainly have done.
This seems fairly complete:
https://www.domguitar.ru/uploads/posts/2013-04/1366375393_3_boss_os2.gif
This is decent discussion of the circuit too, but the schematics leave a lot out:
https://electric-safari.com/2018/10/05/boss-os-2-overdrive-distortion-mod/comment-page-1/

HTH, Good luck!

[duck_arse]

to my untrained eye, all that stuff on the sticking out part of the board looks like flip/flop and switching/routing fets and guff. if you are true bypassing, you can omit all that. pretty much. and as druid sez, get the circuit diagram that is similar, and trace the differences. there mat be much less diff than you'd think.

[ElectricDruid]

to my untrained eye, all that stuff on the sticking out part of the board looks like flip/flop and switching/routing fets and guff. if you are true bypassing, you can omit all that. pretty much.

+1 agree with Duck. That part on the bit sticking looks *a lot* like the two-transistor flip-flop that's familiar from a hundred schematics. It's even laid out on the PCB like the schematic.

That board doesn't look too bad to trace. The parts all have values which helps sanity-check things a lot. The transistors are all marked, for example: "846" (BC846 presumably) and "113" (J113 JFETs for the switching presumably).