Boss DSD-2
A compact digital delay with real sampler guts in a small pedal case. The service manual also admits that its sibling is the same machine in different clothes.
Overview
The DSD-2's spec sheet reads like a delay pedal, but the numbers are odd. Delay time runs from 50ms to 800ms at the maximum. The sampling/delay frequency response is quoted at 40Hz to 7kHz (+1 / -3 dB), which is early digital all over. The input is a 1MΩ FET-input stage, and the output wants to see 10kΩ or more. The listed weight is 450g, printed in the manual as "11bs". Collectors have learned to read past that typo. Signal-to-noise in normal mode is specified at -100dBm or less on the IHF-A weighting.
The documentation is the interesting part. The service notes state plainly that "the difference between DSD-2 and DSD-3 is nothing but the pedal", so the two units are otherwise identical. The same notes say the DSD-2 First Edition service document is superseded and merged into the later revision. That kind of housekeeping helps a lot when you're trying to service one of these decades later.
Internally the DSD-2 is a multi-board unit. The service literature lists an Effect Board (75228520, pcb 2292016801), a Switch Board (75228540), a Volume Board (75228530), a DC Supply Board (75228550, pcb 2291097800), and an LED Board (pcb 2291049600). Replacement boards were supplied as a set of three PCBs rather than individually. Anyone chasing a dead unit should know that before hunting parts. There's also a documented circuit revision. Units prior to serial number 573100 (pcb 2292016800) were built to an earlier layout, and the manual says the circuit was changed for factory reasons with "no performance difference between this and modified one". A low-serial example sounds the same, but it needs a different board.
The calibration procedure shows the digital side of the DSD-2. Technicians set the master clock frequency at the VCO (IC12) by scoping pin 13 of IC4 or pin 18 of IC7 and trimming RT-1 on the Effect Board for a period of 12.12µs (82.5k ±1kHz). That yields a master clock of 5.28MHz ±64kHz at the top end. The low end is set with RT-2 on the Volume Board for a 50µs period (20k ±0.2kHz), giving a master clock of 1.28MHz ±12.8kHz.
Boss's own literature from the period also places the DSD-2 in a wider family. A contemporaneous write-up on MIDI-to-CV/gate gear lists the DSD-2 Digital Sampler among the devices that can be triggered from a gate output, alongside the Boss HC-2 Hand Clapper and the CE-300 chorus.
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