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:
- 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.
- 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 The main op-amp in the DS-1 has been replaced by a discrete version, made up of a differential N-JFET input pair, CCS source load, current mirror on the drain, CCS-loaded PNP common emitter followed by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.
- 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.
- The mode switching uses an additional analog switch to invert the signal for the complementary switches. Nothing too remarkable here.
- 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.
- 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.