Devices such as the TDA7293 and tda1521 were designed in an era when switch mode supplies weren't common in consumer audio gear.
Does anyone know if they are good at rejecting the high frequency noise associated with switch mode designs, or if not, what kind of filtering is needed to make them usable.
Links to datasheets
Philips - datasheet pdf
http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00001887.pdf
Does anyone know if they are good at rejecting the high frequency noise associated with switch mode designs, or if not, what kind of filtering is needed to make them usable.
Links to datasheets
Philips - datasheet pdf
http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00001887.pdf
It is not that class AB chips are designed in a particular way to be able to operate from an SMPS. It is a matter of designing the SMPS such that the output voltages (symmetrical) are as good (or better) as from a traditional power supply. And, a matter of shielding the radiated noise from the SMPS.
Clearly, you cannot just pick up any SMPS and assume it will work well. Also because few SMPS are designed with symmetrical outputs. The SMPS needs appropriate filtering (above the audio band), sufficient output buffer capacitance for decoupling of the amplifier (in the audio band) and a rather quick step response.
Most SMPS are designed for very different purposes.
Honestly, I am not aware of an amplifier that uses one of the "old" chips with an SMPS. Logically seen, if you design with an SMPS (for low weight, reduced size and less heating) why would you then choose an "old" class AB chip that requires a heatsink?
I have myself used a bridged class AB chip (TDA7850) with an SMPS and that worked fine.
Clearly, you cannot just pick up any SMPS and assume it will work well. Also because few SMPS are designed with symmetrical outputs. The SMPS needs appropriate filtering (above the audio band), sufficient output buffer capacitance for decoupling of the amplifier (in the audio band) and a rather quick step response.
Most SMPS are designed for very different purposes.
Honestly, I am not aware of an amplifier that uses one of the "old" chips with an SMPS. Logically seen, if you design with an SMPS (for low weight, reduced size and less heating) why would you then choose an "old" class AB chip that requires a heatsink?
I have myself used a bridged class AB chip (TDA7850) with an SMPS and that worked fine.
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LC filtering is the way to go when powering these kinds of amp chips from switching supplies. They need both normal-mode and common-mode filtering. I did some experiments with TDA8566 which I talked about in this thread : Possibly the most frugal high-end sounding amp?
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