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Old 07-18-2008, 05:46 PM   #1
Insomnia DMX
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Default Sound Card/Diode questions.

I'm thinking of doing a little work with electronics. Most PC sound cards have a microphone input and a speaker output. Of course, if one were to stick a patch cable between the two, one could record the PC's output sound practically losslessly. Sure, there are software alternatives to this where the data is recorded before leaving the sound card, but this would be as plug and play as anything can possibly get. My thoughts led me further; imagine if one had some extra cable and some diodes. There could be another input and another output port, provided one would throw a diode (two if our input is to be stereophonic) to correct for reverse bias. A few switches and additional diodes could be included as well to provide functions like recording only from one source or the other, but both input channels still leading to the output port (external speakers). Heck, if I added many more than one extra input along with a rheostat for each one, the thing could be used to mix several tracks together when one would say, hit record on their favorite recording software (audacity)

My problem is, I don't know what diodes to buy and I know nothing about what kind of current comes out of a sound card. I was hoping you might know something about this stuff or at least point me in the right direction. If you can't help me with any of the specifics, give me an idea for an easy to implement feature I could add.
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Old 07-18-2008, 10:18 PM   #2
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My take on the matter:
Better get an old PC with an old sound card (for which you can get tech docs for). For the output voltage you can do with a multimeter (or voltimeter) but you have to be careful for the 2 probes not to touch themselves (or else it'll probably start smelling like something is burning..).

In the electronic part of it, I apologize but I can't help much more since my electronics knowledge (technical) is almost zero.
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Old 07-19-2008, 12:49 AM   #3
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to For the electronic part of it, he is going to have to go to OM Semiconductor or someother website and search for data sheets. He is going to have to find a diode with proper voltage and frequency characteristics. The diode drop down voltage cannot be too much either. Start by checking out the 1n400x series (i think i have it correct, Cornelleus is closer to school in electronics so he may remember better than me. I have been doing IT for the last couple of years).

With all this said, I am unsure what you are trying o do or even why you need diodes to correct a reverse voltage. I do not get what you are trying to do. Diodes are like check valves. They only allow current to flow one way!

Also, why the mic port? What about the Line In port?
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Old 07-19-2008, 02:10 AM   #4
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Yep, but 1N4000 diode series are a pretty general purpose series, you need high frequency diodes. Also, like Gokuh already said, check for the drop down voltage, the lower the better. Also, be sure not to short the input with an output.

For my old phono albums, I've used, at first, RCA cables. After, I got a pre-amp.

I'll be frank though, like Gokuh, I don't really get what you're trying to do. If you want to record every sounds that your soundcard makes, you better get Total Recorder.

If you want to get into electronic circuits, I highly suggest "Boylestad - Introductory Circuit Analysis", "Floyd - Principles of Electric Circuits" and/or "Floyd - Digital Fundamentals".
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Old 07-19-2008, 02:28 AM   #5
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If I were to stick a mic in the circuit made by the patch cable, we want a diode to block current from going to the mic, we only want current coming from it, right?

This is what I'm thinking of. I probably screwed something up as I don't really know what I'm doing. Plus I don't have much of a symbols vocabulary when it comes to circuit diagrams.



...and what's the difference between the line in port and the mic port?
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Old 07-19-2008, 03:10 AM   #6
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Won't work. Music is, in fact, AC current. It means that, in one period, (1/Frequency) there's 2 half cycle. Meaning, one will get blocked by the diode, but the other will create a short-circuit, cause AC current periodically change it's polarity, changing it's direction at the same time.

The difference between Mic and Line-In are, for short, the decibels and voltage. It means you'll get a clearer sound using the line-in.
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Old 07-19-2008, 03:15 AM   #7
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Thanks for clearing that up. I wasn't too sure this would work in the first place.
I seriously did not know that music was AC...

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Old 07-19-2008, 03:21 AM   #8
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That will not work. The mic will be mono. Your soundcard o/p will be stereo. Further, I believe that the signal from the mic is amplified inside the soundcard. What you will be getting from the mic is a weak signal. If you could get this to work, the output from the soundcard would over power the signal the mic. In other words, you would just hear the music with a bunch of inaudable static attached to it. A very shitty mix - if your lucky

You are better off sticking with software methods. To do what you want to do, you will need to design complex circuits with filters, amps and volume controls. If you do not have filters, you will get some ugly static to your sound from unwanted frequencies and transient signals. You also need to be able to adjust the strength of each signal so the output sounds good to the ear.

Further, with a computer and a sound card you are dealing analog to digital converters and visa versa. For higher quality sound you need high quality AD and DA converters. I am not so sure that you will get he quality you want in a home soundcard.

There is a reason why mixing units are not cheap!

Why do you not use the Line In of the sound card? That is stereo and gives you a higher quality sound. Leave the mic as the mic!
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Old 07-19-2008, 03:28 AM   #9
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Corn....

I guess i got a little more complex...thinking of a standalone device that would use the line in..................

Information Technology makes you dumb!!!! I did not even think of going negative on the line. For whatever reason, I think of a 5V or 12V signal amplitude modulated that never goes negative with a filter cap taking out the DC.

I am just out of touch. Like I said, I am a few years removed from school and i have not used it since!
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Old 07-19-2008, 01:38 PM   #10
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Quote:
Originally Posted by Goku View Post
I am just out of touch. Like I said, I am a few years removed from school and i have not used it since!
Well, my father's an electrician too, so I've worked with electronics since I was young. I remember the time he gave me my first breadboard, good memories.
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