ADDAC 900B Busboard VS.2 (2010s)

This board sits behind the modules and keeps a Eurorack system powered. It has one useful trick.

Overview

It makes no sound, has no blinking lights and takes no patch cables. If your Eurorack system powers on and stays stable, the ADDAC 900B Busboard VS.2 might be the reason. It's a flat strip of PCB with neat rows of pins, tucked behind your modules, and it distributes power from your supply to every module in the row. What sets the VS.2 apart from a generic passive bus board isn't obvious at a glance. It has integrated +5V regulation, pulled from the +12V rail, capable of delivering up to 500mA. That matters for modules that need +5V for logic, displays, or digital brains, like sequencers, screens, or microcontroller-based effects.

Active bus boards include full voltage regulation and filtering on board. The 900B is passive and doesn't regulate +12V or -12V. It relies on your power supply to deliver stable rails, which is standard for most Eurorack backplane designs and follows the Doepfer A-100's original passive architecture. The +5V adapter is where ADDAC adds some real utility. Before this became common, builders either had to wire in a separate DC-DC converter or avoid +5V-dependent modules altogether. The 900B VS.2 puts the conversion circuit directly into the bus board without eating up panel space. For a DIY builder or skiff designer trying to keep things compact and reliable, that's a small victory.

The board uses 14 pairs of 2x8 pin boxed headers at standard Eurorack spacing, so it works with any module that follows the 16-pin power connector norm. The "VS.2" designation suggests a revision, likely improving on earlier versions with better trace layout, cleaner power delivery, or sturdier +5V regulation. Documentation is sparse on the exact differences, but owners report fewer ground loops and cleaner power distribution compared to generic bus boards, especially in densely packed 84HP or 104HP frames. You won't fall in love with it sonically. You notice it when your system boots reliably and your OLED screen doesn't flicker or reset mid-performance.

Specifications

Key Features

Integrated +5V Power Conversion

The standout feature of the 900B Busboard VS.2 is its built-in +5V regulator, which draws power from the +12V rail and steps it down efficiently to supply up to 500mA. Basic passive boards only distribute the standard ±12V and GND. Many modern Eurorack modules, especially those with digital displays, microcontrollers, or FPGA-based processing, require +5V to function. Without it, users have to add external regulators or limit their module choices. The 900B VS.2 removes that hassle for DIY builders who want a clean, integrated solution. The conversion is handled by onboard circuitry, not a bulky add-on, which saves space and cuts wiring.

Low-Impedance Power Distribution

ADDAC markets the 900B as a "low impedance" bus board, meaning the copper traces are designed to minimize resistance and voltage drop across the length of the board. In practice, this gives more consistent power delivery from one end of the row to the other. That counts in larger frames, where modules at the far end might otherwise suffer from sag or instability. It isn't as sturdy as active distribution systems with local regulation, but the layout improves on cheaper alternatives that use thin traces or poor grounding schemes. The boxed headers provide better contact and durability than blade connectors.

Passive Design, Proven Reliability

True to the Eurorack standard, the 900B doesn't attempt to regulate ±12V. It assumes your power supply handles that. This keeps the design simple, reduces heat, and avoids another potential point of failure. For users with a high-quality, well-filtered PSU (like those from PedalPCB, TipTop Audio, or Intellijel), this works well. The passive design also makes it easy to put into custom frames or skiffs without compatibility worries. Service technicians note that failure rates are extremely low. There are no moving parts, no complex ICs beyond the +5V regulator, and the board is built to withstand repeated plugging and unplugging.

Historical Context

When ADDAC introduced the 900B Busboard VS.2 in the early 2010s, the Eurorack ecosystem was expanding rapidly, with more boutique builders and DIY enthusiasts entering the scene. The original Doepfer A-100 passive bus boards had set the standard. As modules grew more complex, with digital displays, USB interfaces, and embedded processors, the need for +5V power became widespread. Many builders were left improvising, adding separate DC-DC converters or limiting their module selection. ADDAC's solution was to integrate the +5V conversion directly into the bus board without increasing its footprint. That put them ahead of many competitors who either ignored the issue or left it to the user to solve.

At the time, companies like Make Noise and Intellijel were beginning to explore active bus boards with full regulation and filtering, but those came at a higher cost and complexity. ADDAC's approach offered essential +5V support while staying true to the modular philosophy of simplicity and user control. The 900B VS.2 wasn't the first to offer on-board +5V, but it was one of the first widely available, well-documented options from a respected modular brand. It filled a niche for skiff builders, DIY frame designers, and small-format systems where space and reliability were paramount.

Collectibility & Value

The ADDAC 900B Busboard VS.2 isn't a collectible in the traditional sense. It doesn't appreciate, isn't rare, and doesn't command a premium on the secondhand market. Used units in good condition typically sell for $40 - $60 on forums like MOD WIGGLER or Reverb. New old stock or unused boards occasionally appear for $70 - $80, which is near the original retail price, so they're hard to justify unless you're building multiple systems. The board has no moving parts and minimal electronics, so failure is uncommon, but the +5V regulator can be damaged by reverse polarity or overcurrent if the system is improperly wired. Collectors and builders recommend checking the regulator IC for signs of overheating or physical damage before purchase. Replacements are straightforward for those with soldering skills.

One quirk: because the 900B VS.2 relies on the +12V rail to generate +5V, it places additional load on the +12V supply. In systems with heavy +5V draw (e.g., multiple modules with OLED screens or USB interfaces), this can lead to +12V sag if the PSU isn't adequately sized. Builders are advised to account for this when calculating total current draw. Every 500mA on +5V consumes roughly 250mA from +12V due to conversion inefficiency. A 2A +12V supply might seem sufficient, but with +5V conversion, effective headroom drops faster than expected. This isn't a flaw in the board, but a design consideration. The 900B VS.2 is best suited for mid-sized systems or skiffs where power demands are moderate. For larger cabinets, a dedicated +5V supply or active distribution system might be preferable.

If you're restoring or building a vintage ADDAC-based system, the 900B VS.2 is a logical choice, especially with ADDAC's own modules, many of which rely on +5V. It's also a favorite among skiff builders for its clean layout and reliability. Newer bus boards from brands like Ghewar or Ciat-Lonbarde offer more advanced filtering or modular expansion. The 900B VS.2 stays a solid, no-nonsense option.

Similar items on eBay

No exact ADDAC System 900B Busboard VS.2 listings are live right now — these searches show current ADDAC System and similar vintage synth gear on eBay:

As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.

Related Models

• ADDAC System 200PI Pedal Integrator
• ADDAC System 213A Eurorack Bridge
• ADDAC System 403
• ADDAC System 705 Dual Noise
• ADDAC System 813
• 2hp DC
• 2hp Fold
• 2hp LPG V2
• 2hp Rash
• 2hp VCM