Impedance Adaptor question... at DVinfo.net

Go Back   DV Info Net > The Tools of DV and HD Production > All Things Audio

All Things Audio
Everything Audio, from acquisition to postproduction.


Reply
 
Thread Tools Search this Thread
Old January 23rd, 2006, 10:54 PM   #1
Trustee
 
Join Date: Nov 2005
Location: Sauk Rapids, MN, USA
Posts: 1,675
Impedance Adaptor question...

I'm using an ATR55 shotgun mic (1k ohm in normal mode) mono to stereo split to an Xl1s 1/8" mic plug (600ohm). I'm trying to make an adapter to get the impedencii to balance out. Were should I put how much resistance? once split, is it 100 ohm resistance on left and 100 ohm on right in series? I'm having to turn the gain waaayyyyy up and it gets hissy. I'm trying to make it better without having to move to different equipment entirely (cheap is better for me, and I'm comfortable with a soldering iron -- just don't quite remember the math for this circuit ... high school was is far away).
Cole McDonald is offline   Reply With Quote
Old January 23rd, 2006, 11:05 PM   #2
Major Player
 
Join Date: Jun 2005
Location: Auburn, Washington
Posts: 218
Jay Rose describes in detail how to make such an adapter in one of his books. You may wish to consult his website or else search the web on impedance matching. Note, too, that DC-blocking is also important on consumer camcorders.
__________________
"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -- Benjamin Franklin, 1759
Doug Boze is offline   Reply With Quote
Old January 24th, 2006, 09:23 AM   #3
Trustee
 
Join Date: Jul 2003
Location: Burlington
Posts: 1,961
Fortunately the XL-1 supplies the mic power on a separate jack, but if you'll use this adapter with other cameras then you will need to block this voltage that Doug mentioned.
In any event, you may not be able to get satisfactory results with an ATR-55, especially splitting the signal. It's a very poor mic.
Jay Massengill is offline   Reply With Quote
Old January 24th, 2006, 07:21 PM   #4
Trustee
 
Join Date: Nov 2005
Location: Sauk Rapids, MN, USA
Posts: 1,675
I'm getting great results for a $25 open box mic at best buy. The biggest problem I'm having is with the audio electronics in the $5000 camera ;).

I disagree with your assessment of the ATR55. The sound is pristine coming directly out of the mic and out of the mic through a wireless transmitter. Good rumbly bottoms and crispy highs. No complaints from me...Yes, I've used high end mics as well, I think the ATR55 wins the price vs. performance war in this case.

I could easily buy a low end sennheiser for $100ish and get 25-30% better sound, but I paid $25 for what is austensibly a good microphone.
Cole McDonald is offline   Reply With Quote
Old January 24th, 2006, 07:58 PM   #5
Fred Retread
 
Join Date: Jul 2004
Location: Hartford, CT
Posts: 1,227
Quote:
Originally Posted by Cole McDonald
I'm getting great results for a $25 open box mic at best buy. The biggest problem I'm having is with the audio electronics in the $5000 camera ;).

I disagree with your assessment of the ATR55. The sound is pristine coming directly out of the mic and out of the mic through a wireless transmitter. Good rumbly bottoms and crispy highs. No complaints from me...Yes, I've used high end mics as well, I think the ATR55 wins the price vs. performance war in this case.
You have to turn the ATR55's gain "waaayyyyy" up because it doesn't put out much voltage. It then sounds hissy because its signal to noise ratio is low, and you're cranking up the noise it generates along with the signal it generates.

When you connect it to a 600 ohm input, most of its alreadly low open circuit output voltage is being dropped across its own 1000 ohm resistance rather than across the 600 ohm input. To answer your initial question, there is no way to increase the voltage applied to the cam's input with resistors. You can only decrease it.
__________________
"Nothing in the world can take the place of persistence..." - Calvin Coolidge
"My brain is wired to want to know how other things are wired." - Me
David Ennis is offline   Reply With Quote
Old January 25th, 2006, 08:02 AM   #6
Trustee
 
Join Date: Nov 2005
Location: Sauk Rapids, MN, USA
Posts: 1,675
yep, lots of research yesterday will have me making a pocket headphone amplifier to set on my camera to boost the signal coming in. I did find out how to get the impedance to match, using resistance in parallel, but I would have to do so sacrificing voltage...which is the actual problem here. So an amp it is! I've also looked into getting an external recorder, but I'm a no-budget guy, so I get to make due with what ever I can make...eventually I'll get a separate recorder, until then, it's the amp and the "good enough" mic.
Cole McDonald is offline   Reply With Quote
Old January 25th, 2006, 03:30 PM   #7
Fred Retread
 
Join Date: Jul 2004
Location: Hartford, CT
Posts: 1,227
I admire your determination. If the amp has a high input impedance, say about 10K, so as to minimize current draw, that'll minimize the noise generated by the mic. That's probably the situation you were getting with the wireless transmitter you referred to. Good luck.
__________________
"Nothing in the world can take the place of persistence..." - Calvin Coolidge
"My brain is wired to want to know how other things are wired." - Me
David Ennis is offline   Reply With Quote
Old February 5th, 2006, 09:55 PM   #8
Trustee
 
Join Date: Nov 2005
Location: Sauk Rapids, MN, USA
Posts: 1,675
The problem was one of voltages, not impedance. I fixed the problem with $8 of adaptors from Radio Shack. ATR55 1/8" mini plug mono to 3.5mm RCA y-splitter into Audio 1 (back of handle) on the XL1s allowed me to reduce the gain making the annoying hiss go away! I'm back to getting moderately great audio! That's plenty good for my purposes.
Cole McDonald is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > The Tools of DV and HD Production > All Things Audio

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 06:21 AM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network