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req help in selecting audio amplifier IC for home 2.1 speaker system

sarath azad
Prodigy 200 points
Other Parts Discussed in Thread: LM1875, LM3668

Could you please help in choosing a audio amplifier IC for DIY home speakers (2.1 system)?

Whether to go for class AB amplifier like LM1875 or LM3668. Or go for a class D amplifier like TPA3116. 

Looking at the datasheets of these class-AB and class-D amplifiers, the performance are looking similar, referring the  graphs for THD+noice vs frequency and output power etc. 

From what I have read, class-D is more efficient and so I may have a smaller power supply driving it and will have smaller or no heat sink. Thus a overall compact and small amplifier will result. But heard they have some EMI issues. 

On the other hand with class-AB amplifier, sound quality will be very good and not sure if these currently available class-D amplifier are producing such sound quality. But they need bigger power supply as they are less efficient, and need a bigger heat sink, so overall it will be bit bulky.

Please help in selecting the suitable amplifier IC for DIY  2.1 channel home speaker system.

thanks and regards

S Sarath

  • 0
    TI__Genius 9175 points

    Hi S Sarath,

    That is a hard question to answer because there are many parameters to consider when deciding upon the "best" amplifier and it often depends on personal preference!

    But here are some of my thoughts from an audiophile perspective:

    Very generally, some of the best sounding amplifiers are the most power hungry. Class AB usually gives the best bang for buck in terms of output power, power consumption and sound quality in this area. That being said, you are correct in that they will generally be bulkier since they operate in the linear region of the active output device. They are always dissipating power even at idle. But for sound quality that is a good thing since the higher idle current consumed for a given output stage, the less of a chance there is for crossover distortion to occur.

    On the other side, Class D is very efficient and can produce huge amounts of power with very little heat dissipation compared to class AB. Therefore it can be packaged into a smaller form.

    The last and perhaps most imprtnat factor to keep in mind is speaker efficiency since this will determine the power needed. Different speakers can require very different power levels.

    For example, if you have speakers that are 85dB SPL @ 1 Watt / 1 Meter, then 40 watts + will be needed  to drive it to extreme levels. Keep in mind, a speaker that is only 3dB more efficient will be twice as loud at the same power!

    So a VERY efficient speaker in the 100+ dB range only needs a 3-5 watt amp to get EXTREAMLY loud.

    I hope this helps,

    -Matt

  • 0 in reply to Matthew Beardsworth
    Prodigy 200 points

    Hi Matt,

    Thanks for the inputs.

    So does Class-D chips sacrifice sound quality for power efficiency or they are comparable with that of Class-AB chips? Looking at the data sheet  graphs they looked similar, not much big difference (THD-noise vs output power, and frequency).

    Will there be any EMI issues with class-d amp chips?

    Regarding speakers I was thinking to use car speakers as here we can get branded car speakers like from JBL, Sony etc, with 4ohm, 30w rms, 90-93db sensitivity.  Is is ok to use car speakers for home tv?

    And regarding power supply I am thinking to use laptop power supply 19.5v, 65w. Is is ok to use this kind of smps power supply or we need to use transformer based linear power supply?

    Thanks and regards

    S Sarath

  • 0 in reply to sarath azad
    TI__Genius 9175 points

    Hi S Sarath,

    You are right in that the THD vs. output power can be very similar between class D and class AB amplifiers.

    As for any perceived difference in sound quality, it will come down to a few factors: speakers, listening habits (active vs. passive listening), and music preferences.

    For example, on a Class D amplifier, the output inductor filters can ring when running. This can be verified by simply running amp with a signal generator and a resistive load. The auditable ringing is not problem because you will never detect it while playing music, however some may argue that this ringing, at the component level, can blur the sound since the inductor is in the signal path.

    Is it a problem? Not really.

    ...Unless you are an audiophile active listener with efficient speakers and are used to running full range drivers without a crossover network and have very good ears….

    There are a few EMI issues to consider with Class D amplifiers. Take a look at this app notes HERE. There is also tons of information on the web.

    Car speakers will certainly work for home use, but you would need to build the proper enclosures to maximize their performance and achieve a full frequency response.

    As for a power supply, a switch mode laptop supply should work fine. I would add additional capacitive filtering right at the chip to handle quick transients. It is common to put something like1000uf in parallel with 0.1uf in parallel with 0.01uf for each channel.

    Regards,

    Matt