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General Category => Technology and Programming => Topic started by: Mince Wobley on February 10, 2008, 09:38:58 pm

Title: Electronics help needed
Post by: Mince Wobley on February 10, 2008, 09:38:58 pm: Hello, I want to make a simple microphone preamp from a schematic I found in the internets, but I am having some trouble with it.

(http://www.gamingw.net/pubaccess/54690/sbmicamp.gif)

What does tip/ring/body mean ?
And also I don't remember how to interpret transistor symbols, how do I find out which lead is the one represented in the symbol with an arrow?
Title: Electronics help needed
Post by: Carrion Crow on February 10, 2008, 09:58:43 pm: http://en.wikipedia.org/wiki/TRS_connector#Tip.2Fring.2Fsleeve_terminology scroll down to Terminology, np man.

Also that's an NPN (http://en.wikipedia.org/wiki/NPN_transistor#NPN) transistor.
Title: Electronics help needed
Post by: Mince Wobley on February 10, 2008, 10:09:05 pm: Hmm I see.

Also, in the schematic and everywhere else it says the soundcard puts out 5v through the ring, but I tried measuring the voltage between the "body" and "ring" and there was none, only between the tip and body, what does that mean? Is my soundcard somehow inverted?
Title: Electronics help needed
Post by: Carrion Crow on February 10, 2008, 10:18:53 pm: It would make sense for the +5v to be the TIP pin because if you look at the way the circuit is wired, when the transistor is saturated (i.e. completely ON) the node above the transistor is practically grounded and when the transistor is off the node should have +5v.
Title: Electronics help needed
Post by: Mince Wobley on February 10, 2008, 10:25:16 pm: I know nothing about electronics except soldering and making PCBs, so does this mean it would or would not work?
Title: Electronics help needed
Post by: Carrion Crow on February 10, 2008, 10:29:10 pm: Make sure you check that it is in fact compatible with your SB card and I think the pin config you have there is a pretty safe bet.

Btw I'm a 2nd year Electrical and Electronic Eng student ;)
Title: Electronics help needed
Post by: Mince Wobley on February 10, 2008, 10:34:43 pm: The voltage on the tip is 2.78 V and it's not really a SB card, it's an onboard card, a realtek AC97.

Now I just cannot understand how PC microphones work on it
Title: Electronics help needed
Post by: Carrion Crow on February 10, 2008, 10:36:48 pm: What's the purpose of the exercise, i.e. why are you making said Pre-amp?
Title: Electronics help needed
Post by: Mince Wobley on February 10, 2008, 10:41:50 pm: It's because I have a dynamic microphone lying around and the circuit is so simple I felt like doing it

--

I had an idea. What if instead of drawing power from that imaginary +5V my sound card was supposed to put out (I found out it just uses an alternative wiring) I used 2 AA batteries for 3V? Like this:

(http://www.gamingw.net/pubaccess/54690/sbmicamp_1.gif)

Do you think it work?

PS : ignore that thing that looks like a ground beneath the "line in body"
Title: Electronics help needed
Post by: Carrion Crow on February 11, 2008, 09:58:33 am: No.
Title: Electronics help needed
Post by: Ruthless X on February 11, 2008, 11:13:54 am: You have to have an engineering of at least 250 to make that work.
Title: Electronics help needed
Post by: Mince Wobley on February 11, 2008, 06:25:34 pm: Quote from: crumply on February 11, 2008, 09:58:33 am
No.

Ok then but why not?

--

I mean, what is wrong?
Title: Electronics help needed
Post by: Carrion Crow on February 12, 2008, 12:50:56 am: It might, but I'm not convinced. You should stick to the power supplied by the sound card and not use batteries because you'll find that in operation 2 AA batteries prolly give out about 2.4-2.6v, never actually 3v.

Tell me if it works.
Title: Electronics help needed
Post by: goat on February 12, 2008, 02:16:19 am: I don't know much about electrical systems, but wouldn't it be more stable to just draw 3.3v from your PSU and reduce it to 3.0?
Title: Electronics help needed
Post by: Carrion Crow on February 12, 2008, 12:29:09 pm: Quote from: goat on February 12, 2008, 02:16:19 am
I don't know much about electrical systems, but wouldn't it be more stable to just draw 3.3v from your PSU and reduce it to 3.0?

This is potentially dangerous.
Title: Electronics help needed
Post by: Mince Wobley on February 12, 2008, 07:30:58 pm: Quote from: crumply on February 12, 2008, 12:50:56 am
It might, but I'm not convinced. You should stick to the power supplied by the sound card and not use batteries because you'll find that in operation 2 AA batteries prolly give out about 2.4-2.6v, never actually 3v.

Tell me if it works.

But my soundcard puts out around 2.7 v anyway I don't think it would make a difference

Anyway thanks I'll post the results here after I build this thing (but it won't be so soon)