VOGONS


First post, by Deksor

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Hi everyone.

Today I tried one of my new SB AWE 64 (CT4500). Drivers installed, fully working, etc ... but once it started to output sound, I directly noticed that nothing was outputed on the left channel. I tried plug my speakers in the speaker output rather than through the line output and the problem was exactly the same.

The card was "stored" in a computer since 20 years (the computer itself is a high-end 1997 PC with an ATX i440LX board and with a Pentium 2 300MHz, but I moved it to my 1998 computer) so the card has no damage whatsoever except a bit of dust but that's all. The caps look fine ... Do you think they could already be dead ? What could be wrong with this card ?

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Reply 1 of 11, by skitters

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Are the speakers working OK with other sound cards?
I ask because my left speaker plugs into my right speaker, and sometimes that connection comes loose when I'm moving the speakers around.

Reply 3 of 11, by Deksor

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Yup the speakers are working fine with all my other sound cards.

I'm going to replace the caps soon. I have to buy many of them anyways

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Reply 4 of 11, by badmojo

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Did you give the audio jack a good clean? I.e. A squirt with contact cleaner and plug / u plug the speakers a few times.

Life? Don't talk to me about life.

Reply 5 of 11, by Deksor

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Well like I said, the card has two audio outputs (line out and speaker out) and both have the exact same problem so I highly doubt the problem is related to the plugs themselves. I tried to move the jack connector a little bit but it didn't do anything

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Reply 6 of 11, by gdjacobs

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It's likely not the TDA chip, then (unless it's shorting the channel). One output will be for unamplified line out, the other will be for speakers or headphones with lower impedance.

All hail the Great Capacitor Brand Finder

Reply 7 of 11, by Deksor

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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 ?

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Reply 8 of 11, by martin939

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I wouldn't touch the values, they're there for a reason. The 470uF probably act as a lowpass/highpass filter, besides filtering out residual DC offset from the chip.
You can try a quick and dirty method - just solder a new cap to the existing one and see what happens when you increase the value.

Reply 9 of 11, by Deksor

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I'd rather fix the card first though ^^

I'm going to buy both type of caps and try both. It's not like it would ruin me ^^

It is known that creative liked to use caps with altered specification to spare a few bucks, so the reason of this could also be "it's cheaper that way"

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Reply 10 of 11, by Jepael

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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.

Reply 11 of 11, by Deksor

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Okay, so far I replaced the two 470µF caps as well as the 4 ones under the TDA chip but it didn't solve anything unfortunately ... I'll replace some other one later

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