4ms Row Power 40 [RP40] (Discontinued)

Name: 4ms Row Power
Brand: 4ms Row

It’s not flashy, but when your rack stays alive and quiet, you know it’s doing its job right.

Overview

The 4ms Row Power 40 [RP40] isn’t something you show off at a synth meetup—it’s the quiet workhorse tucked in the back of your Eurorack case, feeding clean juice to modules that demand stability. Made by 4ms Company, this 4 HP power distribution module was designed to deliver regulated, protected power to one or even two full rows of Eurorack gear, and it does so with a kind of no-nonsense reliability that earns respect the longer you use it. It’s not just a power supply; it’s a system. You can daisy-chain multiple Row Powers together, all fed from a single DC brick, which makes scaling your setup surprisingly simple. And because each Row Power is independently regulated, you avoid the dreaded cross-talk and voltage sag that can plague cheaper or poorly designed power solutions.

Owners report that the Row Power 40 is “a beast,” more than capable of running two 104HP rows without breaking a sweat. One user noted powering a 3-row system at Meme Antenna with just a single Row Power 40 and found it “totally fine.” That kind of headroom is rare in a compact 40W unit. It’s built to last, with high-grade components ensuring each voltage rail—+12V, -12V, and +5V—is cleanly separated and protected. If you’re expanding your modular setup and need a trustworthy power backbone, the RP40 was one of the go-to solutions before it was discontinued.

But let’s be real: it’s not perfect. The Achilles’ heel isn’t the module itself, but the external 4MS Power Brick. Multiple users have reported reliability issues—power cutting out when the connector is jostled, or noise bleeding into sensitive audio paths. One person said their brick “introduced a ton of noise that caused many problems.” Another admitted they’ve had no issues with their Row Power 40s, but only after ditching the stock brick entirely. That’s a recurring theme: the module earns praise, but the power supply it relies on? Not so much.

Still, the design choices show deep understanding of modular users’ needs. The on/off switch cuts power to the module without disrupting the daisy-chain, so you can hot-swap rows or troubleshoot without rebooting your entire system. The input jacks use a split-pin design—meant to grip the barrel plug tightly—but over time, that connection can loosen. A common fix, widely shared in forums, is to gently pry open the split pin with a flathead screwdriver so it grips the plug more securely. Some users go further and replace the entire power brick with a Meanwell or Maplin unit, which are known for better build quality and noise performance. There’s even a suggestion to use a locking DC extension cable to prevent accidental disconnections.

It’s also worth noting that while the Row Power 40 is discontinued, it was part of a broader family that included the RP25, RP30, RP35, and the newer RP45. The RP45 is now the recommended replacement, offering higher output for larger systems. But many builders still seek out the RP40 for its proven performance and compact footprint. And yes, there are documented compatibility quirks—like issues reported between the RP40 and the Pittsburgh Synthesizer Box—but these seem to be edge cases rather than widespread failures.

Specifications

Manufacturer	4ms Company
Module Size	4 HP Eurorack format module
Power Output (Row Power 40)	+12V @ 1.5A, -12V @ 1.3A, +5V @ 1.5A
Total Power	40W (Row Power 40)
Power Input	Powered by laptop-style DC power supply: 2.1mm barrel, positive center, 15V-20V.
Depth (Row Power 40)	27mm (1.1") with power connectors installed.
Included accessories	16-to-16 pin power cable, 2 M3 Knurlie screws (Row Power 40, Row Power 30)
Weight (Row Power 40)	0.15 kg
Dimensions (Row Power 40)	16 × 11 × 5 cm

Key Features

Clean, Regulated Power Rails

Each voltage rail on the Row Power 40 is separately regulated using high-grade components, which helps maintain stable output even under fluctuating loads. This separation minimizes cross-talk between rows, a critical factor when running sensitive analog circuits or digital modules that can introduce noise. The result is a “super clean low noise highly capable power supply,” as one seller put it—something you don’t notice until it’s missing.

Daisy-Chaining for Scalable Systems

One of the smartest design choices is the ability to daisy-chain multiple Row Power units using a single DC power brick—typically supporting 3 to 5 Row Powers per brick. This makes it easy to expand your system without cluttering your power supply setup. The input and output jacks are both 2.1mm barrel connectors, and the input side uses a split-pin design to ensure a tight connection. While this can degrade over time, it’s a small trade-off for the flexibility it offers.

Hot-Swappable Rows and Independent Protection

You can plug or unplug a Row Power 40 without powering down your entire rack. That’s a huge advantage during live sets or soundchecks when you need to swap modules or troubleshoot. Each unit is independently protected, so a short or overload in one row won’t take down the rest of your system. The on/off switch only affects the local module, leaving the daisy-chain intact—another thoughtful touch for modular workflows.

Flexible Installation Options

Beyond the standard Eurorack panel, the Row Power 40 includes blade tabs and solderable headers for custom installations. If you’re building a non-standard case or integrating into a Pod enclosure, these features let you route power without relying on the front panel. Modules connect via flying bus cables or the Bus Stick, giving you multiple ways to distribute power depending on your case layout and cable management preferences.

Visual Feedback and Physical Design

A simple LED indicates when the module is powered—no guessing if it’s live. The unit comes in a matte black panel, fitting neatly into most Eurorack cases. At 27mm deep, it’s not the shallowest module, but it fits in most 84HP and larger cases without blocking adjacent modules. The included 16-to-16 pin cable and M3 knurlie screws make installation straightforward, though some users opt for third-party cables for better strain relief.

Collectibility & Value

The Row Power 40 originally sold for $155.00, but since it’s discontinued, the secondary market is where most transactions happen. A used unit in “Excellent” condition was listed for $110 about four years ago, and another Reverb listing from five years ago showed a “New Price” of $135.90—though current pricing data is sparse. The RP35, which is still available, lists at $145.00, suggesting the RP40 might hold similar value if found in working condition.

The biggest concern for buyers isn’t the module itself, but the external 4MS Power Brick. Common problems include intermittent power loss when the connector is touched and noise injection into the audio path. These issues aren’t inherent to the Row Power 40, but they’re frequent enough that many owners recommend replacing the stock brick. Solutions include using a Meanwell or Maplin DC supply, or adding a locking DC extension cable to prevent disconnections. There’s also a documented incompatibility with the Pittsburgh Synthesizer Box, so users with that gear should proceed with caution.

Maintenance is generally minimal. If the split pin in the input jack has loosened, a quick tweak with a flathead screwdriver can restore a secure connection. No major internal failures have been widely reported, but if a unit does fail, 4ms Company has been known to replace them—there’s at least one user report of a damaged unit being replaced and working perfectly afterward.