Deksor wrote:While checking the caps, I noticed some differences between the caps creative did put and what the TDA recommendations are : […]
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While checking the caps, I noticed some differences between the caps creative did put and what the TDA recommendations are :
The two caps C104 and C105 are 470µF. But it is said that they should be 1000µF
The cap C87 is 100µF, but it should be 2200µF
I knew that Creative did this, but I didn't know that they did it on sound blaster AWE64 too. Since the value AWE64 are apparently a bit noisy, do you think that replacing them with the correct values will help with the noise ?
No, it would not help with noise. If you want HIFI output just use the Line Output, not the Speaker Output.
The datasheet values are suggestions for typical values in a typical environment (most likely typical being car radio or home stereo use). The fact that the chip is used on a sound card leaves room for altering the component values as the environment is different.
So the component values are not incorrect or wrong, nor just altered for the reason to save money. Sure smaller value capacitors could be marginally cheaper, but there might not be even room for larger capacitors.
The 100uF cap is a bulk reservoir cap, there should be a ceramic SMD cap there as well for HF bypassing. Your PC power supply is a switching mode regulator that provides fast response to varying load conditions, so the 100uF of bulk capacitance should be just fine. The 2200uF would be a good value in a car radio, or home stereo with linear transformer based supply.
The 470uF caps main function is to block the half-supply DC offset from amplifier output, but at the same time it a high pass filter for speakers.
For home stereo use you most likely have larger speakers capable of producing 20Hz or 40Hz, but for typical sound card use your speakers are smaller so they cannot produce that low frequencies, so smaller capacitance can be used. The datasheet value of 1000uF makes a low-pass filter of 20Hz with 8 ohm speaker or 40Hz with 4ohm speaker, while 470uF on sound card makes a low-pass filter of 42Hz with 8 ohm speaker or 85Hz with 4ohm speaker. So basically, normal unamplified computer speakers don't need larger caps.
For instance my largest speakers currently are these "bookself" sized speakers (13" × 8" × 11" = 33.0cm × 20.3cm × 27.9cm) , way too large to fit on normal computer desk, and they don't go below 70Hz. And really I don't see the point of connecting this kind of speakers directly to sound card speaker output, but have a proper amplifier driving them from the sound card line out.