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Old April 17th, 2010, 08:50 PM   #1
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Emergency, help with AT899

I hope somebody here can help me because I'm frustrated beyond all belief. I'm getting on an airplane on Wednesday night to fly to California (from Honolulu) to conduct some interviews. Last week Sunday I was doing a final the equipment check and found that I have a bad connection in my microphone Madness Lavalier mic. After doing some research I bit the bullet and ordered an Audio Technica AT899. This will be connected to a Sony HC 7. On the suggestion of B&H Photo, I have a Pearson LMT-100 Low to High Impedance Matching Transformer which terminates in the requried 1/8" plug.

It arrived last night and this morning, I hooked it up to do a test and it doesn't seem to work. I have an extremely high noise to signal ratio (hiss). It's high enough that if the camcorder mic input is set to auto it, attenuates the sound and you can't hear anything. If you switch the camcorder to manual and raise the volume, the hiss makes the recording unusable. This type of equipment is new to me but I suspect I have a bad power module. I'm guessing that I should hear some change, any change, if I remove the AA battery while monitoring the sound. But with a battery in or out, the noise ratio stays the same. (yes, I've changed the battery)

Can anyone help me troubleshoot this issue? I am really running out of time.
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Old April 17th, 2010, 09:40 PM   #2
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Hi Colin...............

Does the HC 7 have a bog standard mic input?

If it's a "real" mic input I can't see what that Pearstone is doing in there, apart from stopping it working.

Your camera should have a standard 200 ohm input impedence, exacly matching the 200 ohm output impedence of the mic.

You MAY need a 3 pin XLR Balanced to 1/8" adapter, but I can't see any reason for the transformer.

Scrounge an adapter from Radio Shack or similar and see if it all comes right.


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Old April 17th, 2010, 09:59 PM   #3
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Thanks for the reply, I am unsure of the input inpedance, but its a 'normal' mini phono plug found on prosumer camcorders and I can't find the spec on Sony's site. I can head over to Radio Shack this evening and pick up another XLR to mini phono plug and check back.
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Old April 17th, 2010, 10:27 PM   #4
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Have you double checked the battery in the power unit? If you have access to a mixer, you could check to see if it works with that - with and without phantom power.
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Old April 17th, 2010, 10:42 PM   #5
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Yeah, the first thing I did was change the battery (twice). I even made sure it was in the proper polarity. (not a joke with my eyes).

Unfortunately I don't have a mixer, but I suppose I could take the mic, cable and camcorder to Radio Shack and bug them. Something in the back of my mind tells me that this is unnecessarily complicated. What do you think about what I mentioned earlier, shouldn't I hear some kind of change with the battery in or out?
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Old April 18th, 2010, 01:15 AM   #6
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Mea Culpa..........

I think I may have led you seriously astray with my last post.

Appologies, I was in "water blast 35 years of accumulated crud off concrete bacony and walkway" mode when I should have been in "Video" mode.

3 pin XLR balanced to 1/8" unbalanced needs a balun, which is what the gizmo is (doesn't say so, but brain eventually kicked in).

Best guess at the moment, take the entire setup into Radio Shack and try another mic with the gizmo (Pearstone) and camera.

If that doesn't work it's got to be either the gizmo or the camera.

Try another gizmo, they should have one, or at least an equivalent.

If that doesn't work.............do the math.

Maybe there's nothing wrong with your original mic?

Once again, appologies, damn, I hate it when that happens.


CS
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Old April 18th, 2010, 01:51 AM   #7
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Some speculation on my part but I just visited B&H at:
Pearstone | LMT100 - Low to High Impedance Matching | 8111240

The 1/8" end is TRS (commonly mislabeled as "stereo) or Tip Ring Sleeve. I ASSUME that this means it is internally wired for balanced output with each pin in the XLR attached to a segment on the 1/8" (one to each of the Tip, Ring and Sleeve).

IF the camcorder is set up to take a STEREO mic input, you'd have 180 degree phase cancellation between the + side and the - side of the balanced mic signal, all but wiping out your signal.

IF I'm correct, you need an 1/8" TS (Tip Sleeve) connector that has has ONE black insulating band, not two.

Again, I can't find any info on what the Sony is expecting but this would certainly account for your issue as stated.

EDIT: OR you could unsolder the connection that goes to the Ring component.
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Old April 18th, 2010, 02:07 AM   #8
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Visited the B&H site and looked at this transformer. One of the comments in the reviews mentioned that his came with a short circuit where the metal strain -relief sping at the 1/8 connector end was making contact with bare wires inside the plug. You might unscrew the connector shell and see if that might not be what's happening with yours.
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Old April 18th, 2010, 02:50 AM   #9
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Quote:
Originally Posted by Shaun Roemich View Post
Some speculation on my part but I just visited B&H at:
Pearstone | LMT100 - Low to High Impedance Matching | 8111240

The 1/8" end is TRS (commonly mislabeled as "stereo) or Tip Ring Sleeve. I ASSUME that this means it is internally wired for balanced output with each pin in the XLR attached to a segment on the 1/8" (one to each of the Tip, Ring and Sleeve).

IF the camcorder is set up to take a STEREO mic input, you'd have 180 degree phase cancellation between the + side and the - side of the balanced mic signal, all but wiping out your signal.

IF I'm correct, you need an 1/8" TS (Tip Sleeve) connector that has has ONE black insulating band, not two.

Again, I can't find any info on what the Sony is expecting but this would certainly account for your issue as stated.

EDIT: OR you could unsolder the connection that goes to the Ring component.
Thanks, I found this discussion elsewhere: Microphone Impedance vs 5D MK II Input Impedance - Photo.net Video Forum
and in it someone posted a reply from Pearson that read:

Quote:
Thank you for contacting the Pearstone Customer Service Desk.

The LMT100 from Pearstone is one of our most popular products.
Without knowing the specific microphone from Audio Technica.
This is where we stand. In general, the standard XLR 3-pin is a mono-connection.
On the mini side of the connection, the mini will provide a dual-mono reproduction
in the camera or recording device.
This method is very common among professionals.

Hope to be of Service,

Joey Quintero
Customer service Pearstone Corporation"
Does this mean that it is wired properly for an (assumed) stereo input on the Sony? Not sure if you can tell anything from this, but I've got a photo of the 1/8" side here:
http://twitpic.com/1gid0t
It appears to me as if everything from the center connector is attached to the center pin(s) in one large solder lump. The shield is on the outer portion of the connector

Quote:
Originally Posted by Steve House View Post
Visited the B&H site and looked at this transformer. One of the comments in the reviews mentioned that his came with a short circuit where the metal strain -relief sping at the 1/8 connector end was making contact with bare wires inside the plug. You might unscrew the connector shell and see if that might not be what's happening with yours.
It does not appear that there is a short, but the plastic inner sleeve is a bit loose and I could see where it could slide a bit.
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Old April 18th, 2010, 02:53 AM   #10
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Originally Posted by Chris Soucy View Post
Once again, appologies, damn, I hate it when that happens.
CS
No problem, hopefully we'll be able to deduce the issue soon
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Old April 18th, 2010, 03:00 AM   #11
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<sigh> I'm confused by the response. Sleep first, answer question in the morning. Unless another heavy weight weighs in on this. I can't tell whether the rep is stating that the T & S are BRIDGED with the +tive signal from the XLR (which would place the input signal equally and in phase in both "right" & "left" channels - a good thing) or something else...
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Old April 18th, 2010, 07:27 AM   #12
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Quote:
Originally Posted by Colin Sato View Post
Thanks, I found this discussion elsewhere: Microphone Impedance vs 5D MK II Input Impedance - Photo.net Video Forum
and in it someone posted a reply from Pearson that read:



Does this mean that it is wired properly for an (assumed) stereo input on the Sony? Not sure if you can tell anything from this, but I've got a photo of the 1/8" side here:
http://twitpic.com/1gid0t
It appears to me as if everything from the center connector is attached to the center pin(s) in one large solder lump. The shield is on the outer portion of the connector

It does not appear that there is a short, but the plastic inner sleeve is a bit loose and I could see where it could slide a bit.
The two centre conductors (tip and ring) in the 1/8 connector should be bridged together so the signal hot goes to them both, while the signal cold / ground should go to the sleeve. It sounds like that's what Pearstone has told you is the way they wire the adapter and your observation of them being soldered together supports that it's wired correctly. It's hard to tell in the photo you posted but it does look right as far as I can see. Alas there's no easy way to test with a cheap multimeter since it's a transformer circuit and there would be no DC connection between the signal hot pin (2) on the XLR side and and the signal hot (tip & ring) on the 1/8 side. And checking for shorts also isn't easy either since tip and ring should be shorted and there's a DC path to ground through the transformer winding so both tip and ring would appear to be shorted to ground as well even when they're wired correctly. So the first step would be to figure out some way to plug the mic itself into something that accepts an XLR mic input where you could listen to it in order to verify that the mic is working correctly. Doing that would tell you if the problem is with the mic, the adapter, or something else. It could also be the jack or other fault in the camera's audio circuits - one of the reasons pro gear uses XLR is its ruggedness - those little 1/8 jacks and plugs can get munged up pretty easily and the springs inside the jacks tend to weaken rapidly leading to noisy or broken connections. If you have a consumer mic with a 1/8 plug, like a computer multimedia mic for example, see if the camera can record from it so you can rule out camera issues.
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Old April 18th, 2010, 07:41 AM   #13
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Originally Posted by Colin Sato View Post
Yeah, the first thing I did was change the battery (twice). I even made sure it was in the proper polarity. (not a joke with my eyes).

Unfortunately I don't have a mixer, but I suppose I could take the mic, cable and camcorder to Radio Shack and bug them. Something in the back of my mind tells me that this is unnecessarily complicated. What do you think about what I mentioned earlier, shouldn't I hear some kind of change with the battery in or out?
The mic absolutely requires power so it will only work with the battery in it when you use it with a device such as your camera that does not supply 48v phantom (nor would any device supply power through the adapter cable you're using). So with the battery out it's guaranteed not to work.
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Old April 18th, 2010, 01:01 PM   #14
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Steve, thanks for your detailed reply. As a test, I plugged another microphone into the 1/8 inch port on the camcorder and it appears to work fine . Just to double check I also plugged both microphones into an older camcorder (again 1/8 inch) and both mics appear to work the same.

I believe I have removed the camera and its port from the equation. I have a short clip showing the differences in the signal level. It is here (and yes, the AT was recorded - it's just really soft):

YouTube - Mic Test.wmv

I will head to Radio Shack with a microphone and cables to see if I can plug them into one of their XLR mixers, but after listening to the clip does this introduce any new things that I should be looking for?
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Old April 18th, 2010, 02:19 PM   #15
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If the camera's external mic input is mono, (two conductor jack ) the Pearstone LMT100 - adapter cable would short out the mic via the 1/8" TRS ring connector as the tip and ring are tied together. If the mic and the adapter cable work otherwise, that's about the only conclusion I can come up with.
If someone has a wiring schematic for the HC7 camera, it could be verified.
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