THX Portable Bluetooth DAC/Amp BTR7 Design Story
Chapter 2 THX AAA Amp Technology-By FiiO Matt
FiiO's Bluetooth DAC/Amps are becoming more mature and stable. The BTR1 first introduced an independent DAC, the BTR3 used LDAC to open the door to high-definition Bluetooth, and the BTR5 is a master, creating a new height for FiiO's Bluetooth DAC/Amps. The BTR5, which has achieved recognition from both the market and users, is a benchmark inside and outside FiiO. Therefore, the BTR7 should first learn from past successful experience, and secondly, learn from user feedback for improvement. Here we would like to share with you the main breakthrough points from the design of the BTR7.
1. The purpose of introducing the THX amp
This is a technology that has been used in many FiiO products. We listened to suggestions from our users and introduced it to the BTR7 after evaluation with the aim of delivering a sound performance close to that of a professional headphone amp. Because after several generations of updates, under the dual role of high-definition Bluetooth LDAC and high-performance audio DAC, there is not much room for a breakthrough in the decoding quality of Bluetooth audio. In order to pursue higher sound performance, it is necessary to improve the audio circuit architecture and power supply. Under this circumstance, THX AAA technology has been applied to the amp part, which can restore high-definition audio while taking into account the quality and looseness of the sound performance. It was the first choice for the independent amp part of the BTR7.
2. Technical challenges and achievements
The BTR7 adopts dual DACs and a 4-channel fully balanced audio architecture. The amps also have 4 channels in the front and rear parts, and the power supply system supporting it also needs to be designed in groups. These difficulties are not in the design, but in how to arrange these circuits neatly and orderly in a compact space and conduct reasonable wiring. Through the efforts of our engineers, this feat was finally achieved on a PCB with up to 8 layers, and a complete shielding cover was even reserved for the amp circuit to enhance the anti-interference ability.
PS: The single-ended output of the BTR7 is 160mW and the balanced output is 320mW, which is close to the output level of mid-range audio players. In addition, when used with over-ear headphones, there is a "Boost bal out mode" in the APP, so that the undistorted power at high impedance can reach 110mW! The 16Vpp swing amplitude can also drive over-ear headphones perfectly.