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Old 6th September 2005, 07:28 AM   #1
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Default Pre amp? What schematic do i need?

Alright heres what i am trying to do and what i have:

I have an Alpine cd player for my car. i installed an auxiliry adapter that converts the Ai-Net(alpines conenctor) to 2 rca female jacks(left and right input). What i am trying to do is hookup a computer microphone to the 2 RCA inputs.

What im wondering is, what type of converter do i need?
Do I need a microphone pre-amp to make this work?

Any info would be helpful. If its a preamp that i need, is there a schematic of a simple preamp that i could build that would just be used for the purposes of doin what i explained above?(not do anything fancy/expensive, i have electrical soldering skills, i just havnt done anything very complicated b4)

Any info would be greatly appreciated.
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Old 7th September 2005, 06:22 AM   #2
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anyone?
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Old 7th September 2005, 06:37 AM   #3
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Well if your not going to use a computer, but only the microphone and hook it up to the cd player, you will most certainly need a microphone preamplifier because the signal from the mic is very very small. If it's a electrostatic mic it will also need a supply voltage.

There are many circuit schemes on the net for mic preamps, i however prefer the Op-amp based ones for the discrete transistor designs but both will work. I built a mic preamp for a while ago. Can see if i can find the schematic.

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Old 7th September 2005, 06:43 PM   #4
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alright thanks, ill look on the net also for some opamp based preamps. is there any that can run on 12 volts? if so i could use the cig lighter lead to run it. most that iv seen are 9volt tho. thanks again
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Old 7th September 2005, 09:29 PM   #5
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Yes you can run them on 12V without problem. But if youre taking the voltage from the cars battery there are many disturbance there. Spikes from the engine and other stuff so you need some filtering to the curciuts.

This circuit should do the trick. You could use almost any op-amp. NE5532 is pretty cheap and good for example. However before coupling it to some expensive car-audio system, try it on some non-expensive equipment first and check it works som you don't destroy anything!
Note also that R5 is supplying the mic with it's voltage. This means you can't connect for example a mp3 player because then you will probarly destroy it. R5 must be deleted if anything else that mic is going to be used.

Here you go, good luck with building

Click the image to open in full size.
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Old 8th September 2005, 06:29 AM   #6
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alright, thanks. one question i have is, on the capacitors, i see that some that are microfarads, they have a posative side but then there areteh one that are nano farads(am i correct?) that have neither + nor negative. thaks for the help so far
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Old 8th September 2005, 05:22 PM   #7
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Yes that's correct. These small capacitors dont have any poles and can be connected in any directions. The electrolytic capacitor has two "poles", a positive and negative side. It must be connected right. Either the positive or negative is always market out on this capacitor!
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Old 9th September 2005, 06:53 PM   #8
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ok this is the last question that i can think of....on the variable resisor is just one end connected to the circuit and then the other end isnt? but the part with the aarow is conencted to the other continuous part of the circuit. im just makin sure before i build this. in a different type of circuit i saw that one end was grounded(the 'end' that just hangs there right now). thanks
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Old 9th September 2005, 07:44 PM   #9
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Yes i understand and this can be varied from circuit to circuit but the cicuit i posted is correct. A variable resistor always has 3 connections with one in the middle which is the arrow. You need only to use two of the connections in this one
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Old 9th September 2005, 08:28 PM   #10
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alright tahts what i thought i was just makin sure:-).

I just got back getting all of the stuff i need, i just have one question about what i ran across. I saw that there was 100 nano farad capacitors that were ceramic and ones that were 'metalized-film'. what ones do i use? i got both kinds. also thre wasnt a 8200 ohm resistor so waht i was going to do is put 2 10kohm resistors in parallel to make it a total of 5K ohm and then on the end of that parallel, i will put a 3.3kohm resistor in series...making it 8300 ohm(am i correct?), will this work or does it have to be exactly 8200?
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