VOGONS


First post, by Deksor

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Today I received this sound card :

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it works, but it's sound is abnormaly low. It's so low that I had to crank up the sound all the way up on my amplified speakers and under mixerset under DOS as well as on the game itself (I tried doom) to get a normal sound. But as one can expect, doing this makes it sound like crap (a lot of hiss sounds, etc)

When I first got the card, these two jumpers were missing :

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I don't think I placed them wrong (I tested both positions anyways), when they are in this position, the card should amplify the sound but it doesn't. The two big amplifiers are still becoming warm so I guess they still work.

What could be the problem here ? Bad caps ?

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Reply 2 of 23, by clueless1

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Did you also turn up the volume wheel on the backplate of the card?

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Reply 3 of 23, by Deksor

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The volume wheel is at it's maximum and dosen't seem to be faulty. I didn't try to clean the jack connector, however as I plugged and unplugged the audio cable several time, that would surprise me but I'm going to try this anyways.

Edit : Tried it and nope, that's not the problem. I tried to change the position of the two jumpers to select if I want amplification or not and the other position is even worse ! So it seems the amps are working ... But there's definitely something wrong on the output circuit somewhere

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Reply 5 of 23, by Jepael

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Deksor wrote:

I don't think I placed them wrong (I tested both positions anyways), when they are in this position, the card should amplify the sound but it doesn't. The two big amplifiers are still becoming warm so I guess they still work.

Good catch with the jumpers.

There's only one amplifier, the TEA2025. I think you are referring to 78XX regulators, yes they do become warm. 7805 makes +5V for analog chips, 7809 makes +9V for the TEA2025 amp.

Deksor wrote:

What could be the problem here ? Bad caps ?

Possible, but extremely unlikely.

Do check if the card gets -12V properly from the power supply, through the ISA bus. Clean ISA connectors. This card should not require external -5V as it should regulate it onboard from -12V. Maybe the -5V regulator is faulty, or something is shorting it's output. Also if you are able to post sharp large images of both sides of the card, we can take a better look. It is of course possible the -12V cap is bad and shorted so nothing in the system gets -12V, but otherwise the PC would still work. Well maybe serial ports not as they usually also need -12V.

Reply 6 of 23, by martin939

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It's is also possible that there are DC-blocking caps, close to the output that are getting bad and start to present a high ESR.
You'd need a scope to trace the signal and see where it weakens.

Is the output also distorted or just low? on both channels equally?

Reply 7 of 23, by Deksor

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I don't have a scope unfortunately. The output isn't distorted, it's just equally low on both channels.

The -12V should be working as the serial ports didn't seemed to have any problems (my serial mouse works, and I could transfer file through serial ports to an Atari ST just fine). I don't know for the -5V, however the PSU is just a good old AT psu, it's not an ATX PSU that has an AT adapter so the -5V should work too ^^

The ISA slot should be clean, I did put two other SB 16 in there as well as my new GUS and all of them worked properly and I plugged and unpluged this card several times because I needed to take a closer look to it. I also cleaned the board itself completely a few month ago.

Yeah I was speaking of the two 78xx regulators ^^

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Reply 8 of 23, by Deksor

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As requested, here are better quality photos (my cellphone camera sucks though, I hope that'd be good enough)

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Reply 9 of 23, by Jo22

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Thank you very much for the pictures! ^^
This makes us helping you a bit easier!

I can't see any damage, so far. Perhaps it's really just the caps ?
Other things from that decade, like Sega Megadrive/Sega GameGear now often have audio issues, too.

I wouldn't be surprised if some blocking caps were gone bad.
All these devices are +25years old by now, after all.

On the other hand, my CT1740s are all still working more less normally, albeit having some noisy audio.
So it's hard to tell what's causing the issue (voltage regulators okay ?).

If you don't know which caps to replace, have a look at the TEA2025 datasheet..
It shows a sample schematic of a stereo amp.

Perhaps it is similar to the one the CT17xx uses. Don't know (it's night and I'm sleepy).
The ALS100+ I fixed, did use it, at least.. So maybe it provides you a hint or so.

Schematic
https://www.build-electronic-circuits.com/amp … ircuit-diagram/

Datasheet
https://cdn.instructables.com/ORIG/FOO/MJEP/I … JEPIEOP5YK8.pdf

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Reply 10 of 23, by Deksor

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Thanks a lot ! I'll look at these when I have a moment. I don't like noisy sound cards much so if that can reduce noise as well, that would be really great ^^

This could help me reduce the noise of another sound card which is the CT2700 (I made a comparison video about some of my sound card here : https://youtu.be/2v6FqmQbs2w It's the second sound card shown). Same for my SB value 2770 which is less noisy but I can still hear some noise there (though in this case I might need to change the PSU's caps as well)

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Reply 11 of 23, by Deksor

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So I looked at the diagram and compared to what I have on my sound card ...

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(Sorry for the poorly made comments but that's probably the best I can do)

So yeah, what creative did there looks fine to me. They just added some more resistors at some points but that seems to be the only modifications .. except for the CMS capacitors as I can't measure them.

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Reply 12 of 23, by Jo22

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Hmm.. I wonder what's the issue then.
It's unlikely, but maybe the TEA is broken anyhow (ESD damage etc.) ?

In case you can't figure out what's wrong, you could install a socket and try a new one.
They shouldn't be that expensive. Replacing the caps would a bit more pricey, but still below ~10€/$10.
Even if the old ones are still working, new ones are a good idea because of their age.

Edit: Your comments in the pic are just fine. :)

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Reply 13 of 23, by Deksor

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Well I was planning to replace every caps, the two voltage regulators as well as the TEA chip ^^

Though when puting the amplification jumpers in the other way makes the sound even lower so maybe it's still working but it doesn't receive enough power ?

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Reply 14 of 23, by Jo22

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That's possible, yes. A broken 78xx sometimes causes the most weird symptoms..
If you're going the replace one or both of them, please note that there are different versions available.
Some support a max. current of about 1A or 2A, while the cheap ones do support less.
So please check the data sheets carefully.

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Reply 15 of 23, by Deksor

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Thanks ^^

If I can't find this information I'll put the most powerful ones, I guess it won't hurt ^^

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Reply 16 of 23, by Imperious

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I assume You have measured the voltages with a multimeter? You haven't mentioned that You have anywhere, unless I'm blind and missed it.

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Reply 17 of 23, by Deksor

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No I didn't, but my multimeter's probes sucks and I fear to rip while the computer is turned on and so making a short circuit. Anyways, something's dying there and this kind of thing isn't really expensive so I just prefer to replace everything that may fail in that area rather than risking to destroy the card ^^

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Reply 18 of 23, by Erik765

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May be over thinking this. I literally just installed one of these in a 286 and had the same issues until I installed the drivers/software. If you're only using a SET BLASTER line in Autoexec.bat, you'll get low volume and won't have cd audio. Install the drivers, ensure the lines are left in (both autoexec and config.sys) and are not REM'd out and it may just resolve this for you... Another tip, once you boot it once this way, you can then REM everything out except the SET BLASTER line and your 'volume' settings will stick (cd audio too). Issue ever arises again, remove REM'd comments, reboot, win. (or just leave all lines enabled all the time if you have the conv mem to spare)

Worth a shot before starting to replace components.

http://www.vogonsdrivers.com/getfile.php?file … menustate=42,35

Reply 19 of 23, by Deksor

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The drivers are already installed ^^ this computer contained an SB 16 before that. I just configured the jumpers of the card like the previous one was. I switched from again another card before that and it worked. If I want to hear something from that card, I have to put all the volumes in mixerset the highest they can, turn the volume knob of my amplified speakers way higher than they were before and turn the volume in the game I want to play the highest too and then I can hear the sound ... Which is highly distorted due to all of this ...

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