Audio Engineering • DIY Hardware
Pusda Speaker Stereo BT System
True stereo with dual isolated power rails. a 3.7V battery powering the MH-MX8 BT receiver and an 8.4V series-pack driving the XH-MX8 amplifier.
Amp: XH-MX8Supply: 8.4V (2S Li)Idle Draw: 0.04AEnclosure: shipping box
▶ demo.webm3 files
01
Dual isolated power rails: separate 3.7V for the BT receiver and 8.4V (2×3.7V series) for the amplifier — eliminates common-ground back-noise completely.
02
True stereo: two independent 4Ω 15W full-range drivers, one per channel, for genuine left/right separation.
03
Insane SPL: at full volume you cannot hear someone yelling beside you. Peak draw 3A on heavy bass; idle 0.04A.
Section 01
Why Two Power Sources?
In Gen 1 a single common ground shared between the MH-MX8 Bluetooth receiver and the amplifier board created a massive hum — digital switching noise from the BT module bled straight into the audio path.
The fix: completely separate supplies.
The MH-MX8 receiver runs off a dedicated 3.7V lithium cell.
The XH-MX8 amplifier board gets its own 8.4V pack (two 3.7V cells wired in series, giving 7.4V nominal and 8.4V at full charge).
No shared ground, no noise floor.
Section 02
Amplifier & Bluetooth Receiver — XH-MX8 + MH-MX8
The MH-MX8 is a compact Bluetooth 5.0 audio receiver/decoder module that handles wireless audio input and feeds a clean line-level signal to the amplifier.
The XH-MX8 is a stereo class-D amplifier board rated for 12–24V DC input with dual-channel output — here driven at 8.4V for controlled headroom that still pushes the 4Ω 15W drivers hard.
Class-D efficiency means the 8.4V pack lasts a respectable time at moderate volumes despite the peak 3A draw during bass transients.
Section 03
The Enclosure — Yes, That's the Amplifier Box
The speaker enclosure is literally the cardboard box the XH-MX8 amplifier arrived in.
It was the right size, already had character, and cost nothing.
Acoustic damping cotton was packed inside to reduce standing waves and give the drivers the impression of a larger chamber.
The result is surprisingly punchy low-end for a cardboard box.
Engineering sometimes means using whatever is on hand.
Datasheet
Project specifications
AmpXH-MX8
Supply8.4V (2S Li)
Idle Draw0.04A
Enclosureshipping box