Simple Stereo Question
Old 22nd April 2012
  #1
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Simple Stereo Question

Hey guys, just built a pretty basic pre-amp for a contact mic that I plan making "modular" with an altoids tin. I want to have jacks for both the input and output of the pre-amp and just solder up a contact mic with a mono plug at the end. So, i'll end up having a mono jack input into the pre-amp, but my question is if I put a stereo plug output for the output of the pre will I run into any problems? I'm not trying to magically make a mono signal from the mic turn into a stereo signal, I just want a stereo output jack on the pre because it will allow me to record into my interface and recorders much easier with their line-in inputs.
Old 22nd April 2012
  #2
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LeeYoo's Avatar
 

A TRS jack socket has an extra contact for the RING.
Up to you if you want to use it, float it, or ground it.
If you shove a mono jack in there, it will be grounded anyway.

Maybe wise to use a "switching" input socket.
These sockets keep the input grounded untill you put a jack in there.
Safer with high impedance inputs.
Leo..
Old 22nd April 2012
  #3
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Be careful though... most laptops are mono. doesn't the ring on a laptop provide power for the mic? That could be a problem if you were to send the + down the tip and ring.


anyway if you always know that you are plugging into a L/R jack, wiring the tip and ring together to feed both sides shouldn't be a problem. And it would be easy to make a jumper that floats the ring for those occasions when you know that you'll be using a mono input, or add a second output jack to your tin that floats the ring.
Old 22nd April 2012
  #4
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Quote:
Originally Posted by Bill@WelcomeHome View Post
Be careful though... most laptops are mono. doesn't the ring on a laptop provide power for the mic? That could be a problem if you were to send the + down the tip and ring.
On most newer laptops the input is combined mike/line, and the mike input is stereo as well. When it's configured as mike input there's power on both tip and ring. Capacitor coupled outputs are necessary in this case.
Old 22nd April 2012
  #5
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Quote:
Originally Posted by Th3_uN1Qu3 View Post
On most newer laptops the input is combined mike/line, and the mike input is stereo as well. When it's configured as mike input there's power on both tip and ring. Capacitor coupled outputs are necessary in this case.
I don't know about "most". I just checked two Lenovo laptops we bought within the last few months, a Compaq and a Dell each less than two years old, none offer line inputs. I miss my old, old laptops with stereo line input, just for running SMARRT.
Old 22nd April 2012
  #6
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LeeYoo's Avatar
 

Am I missing something?
O.P. did not mention laptop input, but interface line input.

IMHI, if you MAKE a MONO device, you use MONO sockets for IN and OUT, and sort out problems on following devices.
A TRS socket can be made mono just by grounding the ring contact.

I use a modified singstar interface as a simple line-input>USB device.
Works for two (stereo) electret computer mics as is, but I ripped the mic-pre out.
Leo..
Old 23rd April 2012
  #7
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Thread Starter
Quote:
Originally Posted by LeeYoo View Post
IMHI, if you MAKE a MONO device, you use MONO sockets for IN and OUT, and sort out problems on following devices.
A TRS socket can be made mono just by grounding the ring contact.
So if I were to use a stereo jack i'd have to ground it in a way so that it becomes just a mono jack? Makes sense, so I guess if I were to just use a mono jack to begin with would there be any problems if a TRS plug is always used with the jack? I ask because a TS plug works on some stereo jacks and on others it doesn't, but on the stereo jacks that the TS plug doesn't work on if I plug it in halfway it will work.

Like I said, i'm only going to be connecting a TRS plug into this pre-amp output and the pre-amp is only designed to be amplifying the mono signal of the contact mic, so does a mono jack output make the most sense in this scenario?
Old 23rd April 2012
  #8
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Scenario 1: Line input is ballanced and you are using a TRS lead. > You have to ground the ring contact of you output socket.
Scenario 2: Line input is ballanced and you are using a TS (guitar) lead. > Ring contact makes no difference.
Scenario 3: Line input is unballanced. > You can use a TRS or a TS lead. > Ring contact makes no difference.
So I would ground the ring contact, or use a mono socket.
Leo..
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