Boss DD-2
A compact pedal that fit a digital delay into a stompbox footprint and made the 1980s rack delay look optional.
Overview
Forty-five to sixty-five milliamps at 9 volts, a single 1MΩ input, and a 450-gram die-cast body the size of a paperback. Those numbers don't look like a digital revolution. The delay time is where the spec sheet gets interesting. The pedal covers 12.5 milliseconds at its shortest up to 800 milliseconds at its longest, across four modes that Boss labeled S.50ms, M.200ms, L.800ms, and HOLD. That last one is the tell: a sampler-grade hold function in a compact pedal, years before "looper" became a category.
The service documentation lays out the mode structure plainly. S.50ms gives the 12.5-50ms range. M.200ms handles 50-200ms. L.800ms covers 200-800ms. HOLD locks in the full 200-800ms window. The delay sound is band-limited to 40Hz - 7kHz (+1dB, -3dB), while the direct signal passes at 10Hz - 60kHz. So the dry signal stays wide open, and the repeats get darker and grainier as the delay time stretches.
Boss also published the residual noise figure at -95dBm (IHF-A), which is a quiet number for a pedal of this vintage. Input impedance is 1MΩ and the output wants to see 10kΩ or more, so it works with anything from a tube amp front end to a mixing console. It runs on 9VDC from either a battery or an AC adaptor. Current draw is 45-65mA, depending on where the delay time knob is parked.
Collectors like the DD-2 for the stereo setup hiding inside a mono-looking pedal. It has MONO and DIRECT jacks, and the DIRECT jack routes only the dry signal no matter how the pedal is switched. In stereo mode with a plug in the DIRECT jack, the MONO jack carries the delay signal only. That is a proper wet/dry split, so you can feed two amps from one compact box.
Know the footswitch behavior before you buy one. The service note is explicit: in S, M, or L mode, releasing the footswitch does not change the control signals to the internal switching transistors, because the flip-flop circuit won't turn over until the next press. In practice the pedal latches. Press once to engage, press again to disengage, with no momentary action. HOLD mode is where this gets musically useful, since the pedal captures and freezes whatever is in the buffer at the moment of the press.
Inside, the DD-2 is built around a 4K D-RAM. That is the HM4864, with a 5K4164NP-20 listed as an alternate, and the service note advises using the HM4864P-3 when replacing for lower current draw. A NE570 compander handles noise reduction, an RDD63H 101 serves as the main controller, and the analog switching runs through an HD14066BP. The service documentation covers a clock frequency adjustment for the VCO at IC8, with test points at IC4 pin 13 or IC7 pin 18. It also has separate high-end and low-end trim procedures on the Effect and Volume boards respectively.
The service note also states plainly that the DD-3 differs from the DD-2 only in the pedal — the rest is identical. That's a useful piece of trivia for anyone trying to date a used unit or source replacement parts.
The DD-2 isn't the most feature-dense delay Boss ever made, and the 7kHz ceiling on the repeats means nobody will mistake it for a pristine modern digital unit. But the 800ms maximum, the HOLD function, and the stereo split give it a musical range that most compact analog delays of the period couldn't touch.
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