ESX QS-FOUR-BT-ISO

Following the great success of the extremely compact 2-channel power amplifier QS-TWO and QS-TWO-BT with Bluetooth®, ESX initially introduced the QS-FOUR, an equally compact and powerful 4-channel version. The demand for a corresponding 4-channel version with Bluetooth was also there, which ESX has now added to its product range.

It is now even available in two variants, which differ only by the ISO cable set. Both are equipped with an integrated Bluetooth module – perfect for wireless audio streaming directly from your smartphone. This is a real highlight, especially for classic and youngtimer cars whose original radios do not have Bluetooth functionality. This allows you to enjoy modern music convenience without having to replace the original factory radio. The classic vehicle appearance remains intact.

Measuring just 90 x 35 x 80 mm, the ultra-compact Bluetooth power amplifier delivers a full 4 x 60 watts RMS. In the test in Car&Hifi issue 6/2025, it was awarded the PRAXISTIPP right after its fantastic introduction and impressed with an even higher output of 4 x 68 watts. And that with an extremely low distortion factor 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 sonically. Often, it is due to the installed radios, which simply deliver too little power. If you want to listen to louder music, the speakers distort. If you then think that it is the speakers' fault, you are mistaken. Because the distortion often comes from the amplifier built into the radio, which is operating at its limit. This is known as "clipping". Only an additional amplifier can remedy this.

However, these are usually very large and must additionally be connected to the battery with thumb-thick power cables. It was precisely for this purpose that ESX developed the QS-FOUR models, which already deliver many times the power of conventional radio amplifiers with over 4 x 60 watts RMS - and that with very low power consumption, the lowest distortion factor, and in state-of-the-art Class D technology.

Thanks to the plug-and-play ISO cable harness in the QS-FOUR-BT-ISO, the power amplifier can be integrated particularly easily into many vehicles – without complicated wiring. Ideal for vehicles with factory radios. The high efficiency of up to 90% ensures minimal power consumption – usually 5 to 10 amperes are sufficient on average.