Amp Control

A self-hosted LAN web app for controlling Monoprice multizone amplifiers (and protocol-compatible clones like the Dayton Audio DAX66) over their RS-232 serial port. Runs on any machine with a USB-to-serial adapter — or a serial-over-IP bridge — connected to the amp, serves a responsive web UI, and exposes a small JSON API.

Tested hardware: only the Monoprice MPR-6ZHMAUT (10761) has been verified on real hardware. The other models below are built to be supported from documented protocol specs but are untested — community confirmation is welcome.

• Per-zone control — power, volume, source, mute, bass, treble, balance.
• Scenes — capture the current state of every zone and recall it in one tap.
• Customizable — rename zones and sources, pick icons, hide unused zones.
• Installable PWA — add it to a phone home screen for an app-like experience.
• Optional PIN — protect Settings from accidental edits, enforced server-side.
• mDNS — reachable at a friendly *.local name with no DNS setup.

The whole frontend is a single static public/index.html (no build step); the backend is a small Node/Express server that talks to the amp over serial.

Screenshots

The Mixer — one card per zone with live state and instant, optimistic controls:

Scenes recall every zone at once; Settings lets you rename, re-icon, and hide zones and sources:

Scenes	Settings

_{Screenshots use a demo configuration — fictional room and source names.}

Supported models

Select your amp with the MODEL environment variable. All of these speak the same ?/</#> RS-232 protocol; only their dimensions differ, so support is just a data profile.

MODEL	Amplifier	Zones/unit	Sources	Max units	Tested?
monoprice-6	Monoprice MPR-6ZHMAUT (10761)	6	6	3	✅ Yes (reference)
monoprice-8	Monoprice 44518	8	6	3	⚠️ Untested
monoprice-4	Monoprice 44519	4	6	3	⚠️ Untested
monoprice-39261	Monoprice 39261 (passive matrix)	6	6	3	⚠️ Untested
dayton-dax66	Dayton Audio DAX66	6	6	3	⚠️ Untested

MODEL defaults to monoprice-6. An unknown value falls back to it with a warning. The 70V Monoprice 31028 is not supported: it uses a different command syntax (not just different dimensions), like the Xantech family.

Hardware

• A supported multizone amplifier (see above), up to 3 daisy-chained.
• A straight-through USB-to-RS232 serial cable/adapter (not null-modem), or a serial-over-IP bridge (ser2net, USR-TCP232, etc.) reachable on the LAN.
• The amp's serial link is 9600 baud, 8N1.

Requirements

• Node.js 18+
• A serial device the host OS can see (e.g. /dev/cu.usbserial-XXXX on macOS, /dev/ttyUSB0 on Linux).

Quick start

One-command install (recommended)

git clone https://github.com/actravis/monoprice-multizone-controller.git
cd monoprice-multizone-controller
./setup.sh

setup.sh detects your OS, installs dependencies, scans for the serial port (or lets you enter a socket:// bridge URL), writes a .env, and optionally installs a background service (launchd on macOS, systemd on Linux/Pi) so it starts on boot and restarts on crash.

Manual

npm install

# point it at your amp and start (MODEL defaults to monoprice-6)
DEVICE=/dev/ttyUSB0 npm start
# ...or over a serial-over-IP bridge:
DEVICE=socket://192.168.1.50:4001 MODEL=dayton-dax66 npm start

Not sure which serial port? List candidates with:

npm run ports        # = node server.js --probe

Then open http://localhost:8080 (or http://multizone.local:8080 from any device on the same network).

Configuration

All configuration is via environment variables — copy .env.example for the full annotated list. The common ones:

Variable	Default	Description
MODEL	monoprice-6	Amplifier model profile (see Supported models).
DEVICE	/dev/cu.usbserial-210	Serial device path, or a socket://host:port serial-over-IP URL.
BAUD	profile default (9600)	Serial baud rate. Ignored for socket:// devices.
PORT	8080	HTTP port for the web UI / API.
AMP_COUNT	1	Number of daisy-chained amps (clamped to the profile's max).
MDNS_NAME	multizone	Advertises http://<name>.local. Empty = off.
CONFIG_PATH	./config.json	Where shared settings are persisted.

These can be set inline (DEVICE=… npm start), exported, or placed in a .env file in the project root (loaded automatically; setup.sh writes one for you).

User-facing settings (zone/source names, icons, scenes, the PIN) are stored in config.json next to the server. This file is created at runtime and is git-ignored — it holds your personal setup and should never be committed.

Security model

This app is designed to run on a trusted home LAN and has no user accounts.

• Anyone who can reach the server can control the amp. Operational actions (power, volume, source, applying scenes) are intentionally open to every device on the network — including guests and any compromised IoT device on the same LAN. Treat reachability as the security boundary.
• The optional Settings PIN is enforced server-side: the PIN is never sent to clients (only a "PIN is set" flag is), changes to protected settings require it via an X-Settings-Pin header, it is compared in constant time, and repeated wrong guesses are briefly rate-limited. It exists to prevent accidental edits — it is not a substitute for network security and is not meant to withstand a determined attacker on your LAN.
• There is no CORS header: the API only accepts same-origin requests from its own UI, so a random website you visit can't script your amp.
• Do not expose this server to the public internet. If you need remote access, use a VPN or an authenticated reverse proxy.

HTTP API

Method	Path	Description
GET	/api/health	Connection status, device, uptime.
GET	/api/zones	State of all known zones.
GET	/api/zones/:zone	State of one zone (e.g. 11–16, 21–26).
POST	/api/zones/:zone	Set attributes, e.g. { "power":1, "volume":20 }.
POST	/api/poll	Force a refresh from the amp.
GET	/api/config	Shared config (PIN value omitted).
PUT	/api/config	Update config (protected keys require the PIN).
POST	/api/unlock	Verify a PIN without changing anything.

Zone attributes accept friendly names or raw codes: power (0/1), volume (0–38), source (1–6), mute (0/1), bass/treble (0–14), balance (0–20, 10 = center). The exact ranges and source count come from the active model profile; GET /api/config reports them under profile.

Running as a service

The easiest path is ./setup.sh, which installs and enables the right service for your OS. To do it by hand, register node server.js (run from this directory, so it picks up .env) with your service manager — a macOS LaunchAgent or a Linux systemd unit.

Development

probe.js and loopback.js are small helpers for testing the serial link and the RS-232 wiring respectively; both honor the DEVICE environment variable. node server.js --probe (npm run ports) just lists candidate serial ports.

Support

This is free, open-source software built in my spare time. If it saved you a headache and you'd like to say thanks, tips are welcome (never expected):

paypal.me/andrewctravis

License

MIT