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I don't use a stencil. Smear paste on the pads, sparingly, and it wicks right onto the pads nicely in the heat. (Only suitable for boards with a solder mask, of course.) This worked really well making 10 TPA3118 boards all at once and all 10 were perfect. And works for the J177 and 2SK208R in my...

Oh, and the choice of 1M or 10K depends on the load that will be put on the bias voltage supply. For jfet input op amps, the input current is very low and 1M ohm is fine and won't drain a battery. But, if you are running from a non-battery power source and have other circuits drawing from that...

This is likely because the op amps used don't have a symmetrical common mode voltage allowed at the inputs. Here's the spec range for a TL072. This means the input voltages for op amp function are from 1.5V above the negative (ground in your case) but can go all the way up to Vcc. So, the ideal...

I use a hot plate to do all the SMT stuff at once. Solder paste on the pads with a toothpick. Stick the parts to the paste. Put the board on the hot plate until the solder all flows. Done. I made some videos of doing this with a TPA3118 board. The solder wicks onto the pads nicely on the hot...

Thanks. I have a laser machine for graphics. So, it only does one color etched to raw aluminum, but I like that aesthetic. I have a BOM in excel format at PCBWay for each. When you order, you will need to specify what parts to install or not.

By the way, if I was going to order them assembled again, I would entirely leave out the drive channel (and pots, LED and LED resistor). Then I would have a small pile I could turn into anything version.

Yes you can order them assembled but they don't seem to have a source for the alpha pots. I've ordered some built and it's not a bad deal but I left out of things that I would need to tweak and install myself.

Yes. This PCB can implement a full AMT pedal in a 125B case if that is what you want. It cannot do the high gain versions, like S2, P2. But, the more gain stages, the more these pedals sound trashy/thrashy. I love the E2 and M2. The O2 is lower gain but really sounds good and is over-drive-pedal...

I've added the O2 schematic and interactive BOM to the PCBWay project. https://www.pcbway.com/project/shareproject/M2_Guitar_module_for_combo_embedded_projects_0a1b466c.html

I've done ear testing between a real O2 and my O2. Mine is better. Really tight, clear, articulate, beefy... Perfect for the amount of gain it is intended to deliver. BAT48 for Schottky, 2SK208R, J177 and 2N5458 all from mouser. All caps in the signal path are polyester film. All caps in the pf...

I have some extras if you want a PCB for the schematic I posted above, if you're in the US. Shipping cost more than it does to order 10 of them from PCBway if you're outside the US. I can post an interactive BOM for the O2 as well or I can share the schematic and PCB if you want to design your own.

Just verified the O2 drive channel schematic is correct since I have a real O2 now...

Also, these drive channels have another gain stage after the volume prior to going to the output and that is embedded in the cabsim after all the footswitching. The FSB1 connector in my schematic is where the drive output would come from a real pedal. I included it on my PCB but do not use it...

Here's the full schematic for my PCB shown with O2 stuffing option on the board. The PCB was designed for B2/C2/E2/K2/M2 so it has a bodge wire to bypass a gain stage for O2.This board fits in a 125B but is meant as the center piece of a combo pedal with extra 9V feeds to all the other modules...

And, I always have the clean channel in my pedals, so I have the input buffer and a feed to the drive on the PCB plus a feed to other drive channels. The combo pedal has a send/return for alternate drive channels fed by the input buffer and selected with a 3-relay ATtiny board. One of 3 drive...

No, but I always have the cabsim in place which has a buffered output. The schematics at freestompboxs has a mistake in the output buffer. They got the push/pull transistor names reversed. I didn't notice that and built a run of PCBs with the mistake. It was easy to use my PCB by changing the...

The specs are virtually identical between 2sk208r and 2sk118r. Use them... Don't worry about the 2n4558. If you have real ones that are within spec, they'll be fine.

Nice. Can see the impact on amplitude on the yellow trace. I'll do some ear testing on the O2 when my BAT41s arrive.

I have a $5K tektronix scope and the picoscope and I use the picoscope almost exclusively because I'm mostly working on audio stuff. It's perfect for audio. The Tek only get opened up when working with digital stuff using 1MHz or higher clock frequencies. The picoscope is useless up there.

I'll get some BAT41. I've been using BAT48 for all my builds and they all sound really good. I don't like the higher gain pedals like S2 and P2. They sound thrashy/trashy to me. That includes the real pedals, not just my builds. Practice testing last night was with active pups into my pedal...