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Old 22nd August 2002, 05:49 PM   #1
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Default newbie post, but hopefully not a newbie question

OK, I've been racking my brains over terms and words that I've been reading in alot of the posts I've searched through so I ask for your patience.

Little background... I'm pretty new to all this. I don't have any formal training so I pickup what I can from friends and forums like this one. I've built a bass guitar but I don't own an amp (yet). To play it, I've been running it through the phono jack of an old Onkyo stereo amplifier. I can see myself blowing out the speakers if I turn it up too much

Here's my DIY question. I've got some LM383 ICs lying around and was wondering if I could use those to build a preamp with a line-level (proper term usage?) output so I could run the signal into my line-in jack on my PC? I'm looking to record my "noise" onto my PC and mess with it there.

If a similar thread exists on this site, I apologize. I blame my lack of understanding which terms to search on.

Thanks
Tim
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Old 23rd August 2002, 05:09 AM   #2
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These chips seem to be 7W Power amp modules. Not exactly what you want for bringing up a guitar to line level. With two of these modules you could possibly build an amp for your Bass guitar (Using two and bridging the output will increase the output to >20W I believe), but again you would want a pre-amp circuit to bring the guitar up to line level. Effects pedals will generally bring the singnal up to line leve (I.E. about 1V) and this can be plugged directly into a line level input on your sound card. This is often why it seems as tho your guitar is louder through an amp with the effect on vs. bypassing. If you don't want to use an in line effect you could try plugging the guitar directly into the Microphone input in the sound card assuming that the card differentiates the two . Mic level is usually much closer to the level of a guitar than it is to line level, therefore a Mic input will often have a preamp circuit built in. If you want more flexability than this, then you might want to build your own pre-amp. There are lots of schematics for guitar and bass pre-amps on the net a quick search should turn one up that will work for you. If you do build a pre-amp just make sure that the output doesn't exceed 2-3V or the Maximum input that your sound card can handle or you'll blow the card.

-D.
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Old 23rd August 2002, 01:11 PM   #3
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Default math formulas?

Thanks for the info. I'll definetly try the Mic hookup.

If I was to try and build a preamp for the computer hookup or for any purpost, is there a site or a thread on this that would explain the math involved? (The signal strength of the bass output vs the required line-level input and what's going to change that?) I went to the links section but they seemed to be all projects and no basic theory.

Thanks again
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Old 24th August 2002, 10:49 PM   #4
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Try digging around on Rod Elliot's web site. There is a lot of theory there. http://sound.westhost.com I find that the best way to completely understand the theory is just to build some of the circuits on a bread board and test them this way. This will work well with preamps as you don't have the high temperatures to contend with. As for figureing voltage output, a good RMS digital meter will tell you this. With a sime wave (I.E. from a guitar) this is only the RMS voltage and multiplying by 1.414 will give actaul voltage. This should be a good starting point. Also, OPAmps are fairly easy to work with and many effects/compressors/mixers use these. I know there are quite a few designs for preamps on the web using OPAmps.

-D.
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