BOSS DS-1W waza craft [schematic]

[dylan159]

Despite having been around for some years, there's still an aura of mystery around waza craft BOSS pedals. What do they have in common, what is the "waza" factor? What do the custom modes even do?
There's some info thrown around about CCS-loaded buffers, which are nice even if unnecessary for guitar, and they're still just buffers. Is that it?
That said, I have the luck of having a friend who owns the DS-1W and who let me borrow it for tracing without begging too much. Thanks to him, and my hard work, we have what I think is the first traced schematic of a DS-1W:

There's another person that deserves credits, and it's kanengomibako, who traced the BD-2W, a work deserving of its own thread here of FSB but was hard to find. There's not much the two circuits share in the end, but I was able to double-check my guesses on the parts numbers of the transistors and diodes based on their schematic. As you might know, markings on SMD parts, if any, tend to be hard to read and very generic. And these are very small parts, smaller than what I usually see in pedals. In fact, each transistor marking could belong to three or four different devices, although they are all equivalent in function, pinout and specs. I've noted the actual marking for transistors and power supply diodes just in case.

Let's get into some circuit analysis. I will skip over the basic DS-1 circuit and focus on the differences:

1. CCS loads. Input JFET buffer, JFET differential pair, amplifier and buffer at the op-amp output all feature a similar CCS load, with a NPN transistor biased by two diodes and emitter degeneration. The output buffer is resistor loaded.
2. Op-amp. The main op-amp in the DS-1 has been replaced by a discrete version, made up of a differential N-JFET input pair, CCS source load, current mirror on the drain, CCS-loaded PNP common emitter followed by CCS-load NPN emitter follower on the output. This is one step further than the simpler discrete op-amps also used by BOSS in other circuits, and at least some of the reason is to have high open-loop gain to achieve the high closed-loop gain of a DS-1. That said, it's so close to the internal schematic of some simple integrated op-amps one has to wonder why not just use the premade thing at that point.
3. Custom mode. The "waza mods" in this pedal are many, handled by a combination of analog switches and JFET switches.
   • Series capacitor and resistor (R43+C30) are switched in parallel to the top half of the feedback divider.
   • Another series capacitor and resistor (R36+C26) are switched in parallel to the grounded leg of the feedback.
   • The custom mode has two diode pairs in series for clipping, with a series resistor, instead of a single pair.
   • The high-pass capacitor in the tone control is larger, shifting the cutoff lower.
   • The low-pass capacitor in the tone control is smaller, shifting the cutoff higher.
   • The volume control is tapered in custom mode, but this mode is still noticeably louder.
   Overall, those changes all contribute to make the pedal louder and more mid-focused, which I guess are the usual complaints by people that don't like the DS-1. I already have a simulation of the tone control made, so it's easy to show the tone control differences. I've included the loading effect of R71 on the custom version.

   

4. The mode switching uses an additional analog switch to invert the signal for the complementary switches. Nothing too remarkable here.
5. This is the first time I've seen BOSS deviate from their usual discrete transistor implementation of the bypass flip-flop. The switch voltage is first cleared up by a single Schmitt trigger (marking "HA", considering the pinout this is the only thing that makes sense), then fed to a D-type flip-flop IC. Since these two logic circuits are powered with a dedicated 5V supply, the outputs have to be level shifted to 9 V to be compatible with the usual JFET bypass switching.
6. The main power supply rail is regulated and filtered by a discrete regulator. I've measured the Zener voltage to be 9.1 V and the output to be 8.45 V, but I included the diode markings anyway. The discrete regulator is repeated for the 5 V supply, just as extra protection against overvoltage, and then fed to a 5-pin regulator that outputs 5V (measured). The only parts compatible with the marking "A28(2)" are 2.8 V regulators and dc converters, but I've reported the correct pinout, connection and output voltage on this board.

Finally, some pictures of both sides of the board for who's curious. They're pretty standard for new BOSS pedals, with maybe a bit more attention to detail.

Final notes: while I'm pretty confident in this schematic, especially for the signal path, this is still a traced schematic and it's not guaranteed to be free of errors. I've noted each part I've drawn in the schematic on a picture on my tablet, so at least all components should be accounted for. Not all resistors had markings, some being very small and uniformly yellow, but I've measured them both ways and was able to get accurate readings that are very close to standard values, so those should be fine. The only exception might be R54 and R70, but those don't really matter much. Desoldering capacitors on a new borrowed pedal would have been an abuse of my friend's generosity, so SMD capacitors don't show a value. Thankfully though, any capacitor that has a value of some relevance for the sound is instead a THT polypropylene capacitor, so I could write values for those.

[soulsonic]

Thank you for your work! An early birthday present for me!
It's exciting to see 2SK880 being used in a commercial guitar pedal. This is the first time I've seen it used in a pedal outside of my own designs. I started using them a few years ago when 2SK117 became impossible to get, and I really like them.
Also cool to see them using a discrete opamp. Overall, I am very pleased with the design ethic I see here.

[dylan159]

Thank you for your work! An early birthday present for me!
It's exciting to see 2SK880 being used in a commercial guitar pedal. This is the first time I've seen it used in a pedal outside of my own designs. I started using them a few years ago when 2SK117 became impossible to get, and I really like them.
Also cool to see them using a discrete opamp. Overall, I am very pleased with the design ethic I see here.

It could be 880, it could be 209, the two have the same specs and the same markings. Either way, the way they're used makes sure almost everything could work with little adjustment. There's no reason to keep using only J201 and 5457 either.
I don't share many design choices, but the use of a discrete op-amp in a DS-1 almost makes sense, since there's only one and it's expected to saturate. Either way, I actually like the custom mode. If I were to remake it, I'd probably cut down a few things while keeping the high open loop gain.

[lrgaraujo]

It could be 880, it could be 209, the two have the same specs and the same markings. E

The 880 is actually TINY. I think toshiba packages have different names, but the 2sk209 is equivalent to a sot-23 and the 2sk880 is equivalent to a sot-323.

[Jarno]

Wow, that is actually quite fancy, quite a lot discrete semiconductors. Cool, do wonder why they haven't used an internal smps to up the power supply voltage, since they have used a dedicatedncircuit for the bias voltage.

[dylan159]

Wow, that is actually quite fancy, quite a lot discrete semiconductors. Cool, do wonder why they haven't used an internal smps to up the power supply voltage, since they have used a dedicatedncircuit for the bias voltage.

Can you explain me what you meant? The supply is only stepped down and the bias voltage is made from a resistor divider as usual (or diodes for the CCS).

[dylan159]

It could be 880, it could be 209, the two have the same specs and the same markings. E

The 880 is actually TINY. I think toshiba packages have different names, but the 2sk209 is equivalent to a sot-23 and the 2sk880 is equivalent to a sot-323.

Ha that's right, it's not evident from the datasheet and both say "small package", but the 880 is smaller if you look at the measurements.
The transistors in this were all sot-23 sized; those dual diodes though, oh boy.

[soulsonic]

I can tell you from experience that you can solder the 880 to the footprint for a SOT-23, but you have to be very careful. Don't sneeze on it.

[Jarno]

Wow, that is actually quite fancy, quite a lot discrete semiconductors. Cool, do wonder why they haven't used an internal smps to up the power supply voltage, since they have used a dedicatedncircuit for the bias voltage.

Can you explain me what you meant? The supply is only stepped down and the bias voltage is made from a resistor divider as usual (or diodes for the CCS).

Looked at it again, I mistook the flipflop IC for a PSU part, LOL

[lrgaraujo]

Ha that's right, it's not evident from the datasheet and both say "small package", but the 880 is smaller if you look at the measurements.
The transistors in this were all sot-23 sized; those dual diodes though, oh boy.

I've learned it the hard way

I can tell you from experience that you can solder the 880 to the footprint for a SOT-23, but you have to be very careful. Don't sneeze on it.

I've adapted the sot-323 footprint on eagle to be a little easier to etch and solder, which, now that I think of it, makes it very similar to a sot-23 footprint