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Old 30th March 2008, 06:36 AM   #1
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Default Gainstage for soundcard.

Hi

I have a Soundblaster Live! 5.1 in my PC and it works great with one exception: if one tries to use the mic, line in or aux in (internal), you have to crank up the input levels as high as possible and still the result is very low volume (signal). For me the problem is when I use my tv-card for recording so I thought I'd solve the problem with a preamp or such between the tv-card and the sound-card (aux, internal. Most conveniant).

Built a preamp (the basics are actually the volume stage from one of Rod Elliotts preamp projects, with a couple of changes) and used the ne5532. Works great as preamp, surprised at the high sound quality (for the low cost). Anyway, plugged it in between the tv-card and the soundcard but the "preamp" didn't do that much of a improvement. Built another one with slight changes (attached picture) and thougt I'll get more gain with this one but no luck.

Is it a question of tuning the "preamp" to get it to add a little bit of gain to the signal from the tv-card or do I need to add another gain section. Or wount it simple work at all . I'm no wiz at this but I think I got the basics and stuff (or do I?)

Thanks for any help
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Old 30th March 2008, 07:18 PM   #2
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Well, you could increase that 11k pictured in your negative feedback loop, NFB, up to some larger figure for more amplification. Its barely doing any amplification at present.

Although, the problem with your TV card is quite unusual because most TV cards are so loud that they clip. What's the make and model of the TV card?
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Old 30th March 2008, 09:45 PM   #3
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Ok. 20k, 50k ? How much or how high can i go (roughly). The tv-card is a winfast tv2000 xp expert and the problem is the inputs on the soundblaster. Had both of them in my previous comp. and also tried with a onboard soundcard (c-media). The c-media lacks in sound quality and the drivers creates conflicts with the rest of the comp (but the signals in comes out strong, normal).

I doesnt matter what I hook up to the inputs on the SB, the signal comes out week. No problems with sound quality otherwise, "accurate", no noise or distortion. A good card so...

Well, gonna increase that 11k and see what happens. Thanks.
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Old 30th March 2008, 09:57 PM   #4
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I would guess, given the two options, that the 20k is closer to specs for the op amp chip.
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Old 30th March 2008, 10:23 PM   #5
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Ok. Gonna start with 20k then and see (hear) whats what. Thanks.
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Old 31st March 2008, 09:14 PM   #6
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Hooked up a 44k pot along with the 11k and it seems that a total of 55k isn't a problem, much more gain but a bit "harder" sound at high volume (no surprise). Had it running with single 12 volt earlier and it worked well but had to change to -+12 volt now. Gonna test it in the comp later and see how it works.
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