ESX QS-FOUR-BT - 4 Channel Nano Amplifier with Bluetooth Receiver

Features

Efficient Class D Amplifier with ultra-compact dimensions
Heavy die-cast Heatsink with perfect cooling characteristics
Auto Turn-On Function
High Level Inputs with Error Protection System (EPS®)
Start/Stop Ready

RCA In- and Outputs (via Cable Connector)
Stereo RCA Output for e.g. active Subwoofers
HPF/LPF switchable
Perfect for HD-Audio
With integrated Bluetooth Receiver

Specifications

• 4-Channel Class D Plug+Play Nano Digital Amplifier
• with integrated Bluetooth Receiver
• 4 x 35/45/60 Watts RMS @ 4/3/2 Ω
• 2 x 120 Watts RMS @ 4 Ω bridged
• 2 x HPF/LPF @ 80 Hz
• Frequency Range 10 Hz - 60 kHz
• Dimensions 90 x 35 x 80 mm
• Efficiency up to 90%

Following the great success of the extremely small sized QS-TWO and QS-TWO-BT 2-channel amplifiers with Bluetooth®, ESX initially introduced the QS-FOUR, an equally small yet powerful 4-channel version. The desire for a corresponding 4-channel version with Bluetooth was also evident, and ESX now offers it.

It is now available in two versions, differing only in their ISO wiring harness. Both feature an integrated Bluetooth module – perfect for wireless audio streaming directly from your smartphone. This is a real highlight, especially for classic and vintage cars whose original radios lack Bluetooth functionality. Enjoy modern music convenience without having to replace the original factory radio. The classic look of the vehicle remains intact.

Measuring just 90 x 35 x 80 mm, this ultra-compact Bluetooth amplifier delivers a robust 4 x 60 watts RMS. In the test in Car&amp Hifi issue 6/2025, it was awarded the PRACTICAL TIP after its outstanding performance and impressed with an even higher output of 4 x 68 watts. And all this with an extremely low total harmonic distortion of just 0.008% (THD+N @ 5W) and excellent sound quality.

Once connected, the ESX QS-FOUR-BT will amaze you. Even factory speakers can be improved in terms of sound. Often, the problem lies with the built-in radios, which simply don't deliver enough power. If you want to listen to music at a higher volume, the speakers distort. If you then think it's the speakers' fault, you're mistaken. Often, the distortion comes from the radio's built-in amplifier, which is operating at its limit. This is known as "clipping." The only solution is an external amplifier.

However, these are often quite large and require thick power cables to be connected to the battery. ESX developed the QS-FOUR models specifically for this purpose, delivering over 4 x 60 watts RMS – significantly more power than conventional radio amplifiers. And all this with very low power consumption, minimal distortion, and state-of-the-art Class D technology.