Impedance Adaptor question... at DVinfo.net

Cole McDonald · January 23rd, 2006, 10:54 PM

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).

Doug Boze · January 23rd, 2006, 11:05 PM

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.

Jay Massengill · January 24th, 2006, 09:23 AM

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.

Cole McDonald · January 24th, 2006, 07:21 PM

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.

David Ennis · January 24th, 2006, 07:58 PM

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.

Cole McDonald · January 25th, 2006, 08:02 AM

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.

David Ennis · January 25th, 2006, 03:30 PM

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.

Cole McDonald · February 5th, 2006, 09:55 PM

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.

January 23rd, 2006, 10:54 PM	#1
Cole McDonald 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).

January 23rd, 2006, 11:05 PM	#2
Doug Boze 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

January 25th, 2006, 03:30 PM	#7
David Ennis 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

January 24th, 2006, 09:23 AM	#3
Jay Massengill Trustee Join Date: Jul 2003 Location: Burlington Posts: 1,976	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.

January 24th, 2006, 07:21 PM	#4
Cole McDonald 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.

January 25th, 2006, 08:02 AM	#6
Cole McDonald 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.

February 5th, 2006, 09:55 PM	#8
Cole McDonald 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.