BOSS DS-1W waza craft  [schematic]

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dylan159
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Post by 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:
ds-1w.png
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 The main op-amp in the DS-1 has been replaced by a discrete version, made up of a differential N-JFET input pair, CCS source load, current mirror on the drain, CCS-loaded PNP common emitter followed by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.
    wazads1.png
  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.
front.jpg
back.jpg
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.
Last edited by dylan159 on 27 May 2023, 11:59, edited 2 times in total.
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Post by soulsonic »

Thank you for your work! An early birthday present for me! :D
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.
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Post by dylan159 »

soulsonic wrote: 24 May 2023, 00:45 Thank you for your work! An early birthday present for me! :D
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.
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Post by lrgaraujo »

dylan159 wrote: 24 May 2023, 08:48
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.

Image

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Post by 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.
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Post by dylan159 »

Jarno wrote: 24 May 2023, 19:51 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).
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Post by dylan159 »

lrgaraujo wrote: 24 May 2023, 14:13
dylan159 wrote: 24 May 2023, 08:48
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.

Image
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.
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Post by 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. :lol:
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Post by Jarno »

dylan159 wrote: 24 May 2023, 19:57
Jarno wrote: 24 May 2023, 19:51 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 :)
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Post by lrgaraujo »

dylan159 wrote: 24 May 2023, 22:10 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 :blackeye

soulsonic wrote: 25 May 2023, 02:14 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. :lol:
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 :D

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Post by dylan159 »

Hello again everyone! Soon after tracing this circuit, I felt like it would be nice to have a simpler, DIY friendly version. I've called it DS-R, which stands for "Reasonable": it's a pretty hefty circuit, but I've sized things down when possible. I think it would be fitting to share it here, since it's an adaptation of the BOSS circuit.
I've thought the DS-1 is a nice candidate for using a discrete op-amp, if there's one, because it needs only one of them, and it has some chance to make a positive difference since the diodes don't prevent it from saturating (I think there's some difference between chips there, but so far my test have been inconclusive). That's another reason for being "Reasonable".
ds-r.png
The changes made are:
  • Removed all the electronic bypass and mode switching, of course. Using a 4066 for the mode switching is still a pretty good idea, but I leave that choice to you.
  • All the current sinks have been turned into resistors. I don't think any of the advantages they bring matter here, or for guitar in general. The resistors have been chosen for currents which are close to the ones of their respective sinks.
  • The sound of the DS-1 relies in small part on the high-gain common emitter stage driven by the low source impedance of a follower. I'd have gladly skipped the follower otherwise, but the only other options would be to shift this gain to the op-amp, or to put another op-amp there, neither of them seeming great in this instance. The input buffer is BJT, run at sub-200 mA current to optimize noise, and is as good as it can be.
  • The discrete op-amp uses BJTs for the differential pair. It turns out that the one used in the DS-1w is remarkably similar to the "audio preamplifier" IC used in the oldest DS-1, except for that one being fully bipolar. So, in a way, this is closer to the vintage one in this regard. Not using JFETs at all helps with ease of building, and they're not necessary, with their lack of input bias current, since the stage isn't right at the input and is AC coupled. Open loop gain is just as high, and closed-loop frequency response matches perfectly the waza in simulation.
  • I've divided the "custom" switch into two, one controlling gain and clipping, one controlling the tone-stack flattening, so they can be common DPDT.
    Note even if you're not interested in this version
    Testing this circuit led me to an obvious (in hindsight) mistake with R36 and C26 in the traced schematic. As they're shown there, the gain stays high no matter what in "custom" mode, which doesn't match my experience. The wiring is probably right, given they've split a resistor there, but maybe the value of the resistor is off by a factor of 10? That still results in a bit too much gain, but is less extreme. Maybe this is something someone else can check, since I don't have the unit; I've done the hard work already :wink:
    This is why I've decided to leave out those two components completely, which allowed me to condense the gain and clipping switches and gives the best results. As a consequence, the feedback path has been simplified greatly.
  • The tone stack and output and pretty much the same, just with fewer coupling capacitors, given the absence of the bypass muting.
  • The power supply section has been simplified: no discrete regulator, but just a capacitance multiplier to keep the input stages free of noise (and it's a very BOSS thing to do).
Here's a demo, if you're curious:
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