Class D Audio Amplifier Design TDA7498

Posted on Feb 6, 2014

A couple of years ago I decided I would (eventually) need to replace my decades-old Nakamichi stereo with something more suited to a mobile lifestyle. It was immediately pretty obvious that the Class-D and E switching amplifiers I had researched in the `70s were experiencing a renaissance. Tripath had come and gone, but its excellent chipsets rema

Class D Audio Amplifier Design TDA7498
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ined available from China. ST had a few nice chips, as did National Semi, Texas Instruments and IR. I quickly found that the science developed in the `70s, a deep understanding of the differences between switched amplifiers and linear amplifiers, seems to have been forgotten. Sure, the chipsets are really excellent, but the component selection in the application designs seemed to be pretty woeful. Since most of the new chips have a feedback loop which doesn`t include the output filter circuit, poorly designed filter networks were limiting the performance of most of the amplifier modules commonly available. I have been playing with several chipsets, those which I think have the most potential for value-HiFi, and I am going to use the ST TDA7498 chip to illustrate how not to design a quality audio amplifier, and how inexpensive it can be to design a good one. ST don`t supply boards for the TDA7498, so I bought some assembled PCBs on Ebay from Sure Electronics (for the princely sum of $22)(#AA-AB32165). Although they were advertised as TDA7492 boards, several arrived with TDA7498 on them, but the last one came with a TDA7492. So haggle with the seller a little, if you need to operate above a 24V supply rail. I was able to change the chips, but I needed my special surface mount rework tools. SURE assembles these PCBs identically for both CPUs, except that the fan power supply components are added for the TDA7498 version. I...

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