Impedance Matching XLR to 3.5mm Mini-plug

mhbstevens wrote on 2/7/2005, 8:53 AM
In a thread relating to my search for a hand-held stick mic to be used with the Sony FX1 for on-camera interviews I became aware of both the problems finding a pro mic for a 3.5mm mini-plug input and the fact that I was confused regarding the whole subject of impedance matching "Low Z" XLR output pro mics to high impedance camera input mini-plugs as on the FX1.

I have just re-read the "Working with Audio" section of Spot's book "Digital Video Basics" but I am still not able to use the info thererin to direct me to the mic and cables I'm looking for. Here is the source of the confusion I solicit help with.

As the FX1 has mini-plug imputs I wish to have a mic with a mini-plug out to keep it simple, but Spot has said such an animal does not exist at the quality level. So if I buy a mono stick mic with a XLR out how do I connect it to the FX1 without using a bulky XLR audio adapter.

Spot mentioned an "XLR to mini-plug" cabel but I also see advertised a low to high impedance transformer like the Shure A96F. Is this an alternative to the cable or do I need add this as well? And if so should the transformer be just before going into the camera?

Could I use one of the cheaper stick mics that DO have mini-plug cabels or are these really bad? I guess they are "high Z" mics?

The FX1 is a top end camera so I am wondering what did Sony see me buying for street interviews or did they expect me to add a XLR mixer box at the camera like I was trying to avoid?

Suggestions for mic/cabel combinations sought with much thanks advanced in anticipation.

Cheers,

Mike Stevens

Comments

DavidMcKnight wrote on 2/7/2005, 9:05 AM
The nature of the solution is a transformer, regardless if it is in a cable, bulky adapter, or some type of direct box. I'm not familiar with cables that have the transformer in them, but for videographers the most commonly used adapter is a Beachtek or Studio One. Here is a link to one of their products, it can depend on the the camera you have as to which one you buy.

http://www.beachtek.com/dxa4.html

Hope this helps, let us know.

- David
Orcatek wrote on 2/7/2005, 9:09 AM
Wouldn't something like this work

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=274-016
filmy wrote on 2/7/2005, 9:27 AM
I use an XLR-PRO made by Studio 1 productions. They have revised these and the newer models are part of the XLR-BP series. I love my XLR-PRO and it is a must for tieing into things like soundboards.

On the XLR to mini adapter/transformer I use a Shure, model number A97F. The "manual" PDF is available here: a97f.pdf.
musicvid10 wrote on 2/7/2005, 10:41 AM
Rather than a bulky transformer at the camera input, a passive or active direct box on the floor is your answer. Plug your xlr into the box, plug a cord with 1/4" into the box and 3.5 mm on the other end to your camera, and shoot away. They all have ground lift capability.

Passive boxes come in many flavors, and I like the little DB25 from Rolls.
Active boxes are made by Behringer, M-Audio, and several others.
riredale wrote on 2/7/2005, 10:42 AM
The XLR connection has been around for many years, but the miniplug can do an amazingly good job, too. You can find some high-quality mics with miniplug connections because manufacturers realize this, too. I commonly run 40' over SHIELDED miniplug cabling with no issues at all; just make sure you buy shielded cable. I once did a 90' run from a miniplug mic to recorder, again with no problems. The XLR connectors are much more rugged, however, which for field work would be an important consideration.

With my VX-2000 I use a $250 Audio-Technica AT-822 stereo mic, which offers connectors for both XLR and miniplug situations. I have a good friend with a $500 Rode NT4 stereo mic that also provides for either XLR or miniplug.

So from my experience to date, miniplug works fine for most applications.
Laurence wrote on 2/7/2005, 7:54 PM
Here's another vote for the Studio 1 XLR-BP Pro. I have one that I use with my VX-2000. If anything it's more convenient than having the XLRs on the camera. The weight of the XLRs is on your belt and the camera is easier to handle. Compared to a Beachtek the balance on a tripod isn't thrown off. I really like my BP-Pro.
mcgeedo wrote on 2/8/2005, 6:17 AM
If you or someone you know is a bit of an electronics tech, here is a way to do it small. At Radio Shack you can buy a little transformer (1:1 audio). It will fit inside a large XLR connector shell. You can wire a cable with the miniplug to it. I made on of these for a wireless mic receiver that velcro's to the back of my big cam. The receiver has a minijack output and the cam has an XLR in. Same principle, though.
craftech wrote on 2/8/2005, 8:16 AM
The microphone input on the FX1 is no different than the one on the VX2000 or the VX2100. Anything that works on those two will work on the FX1.
The most versatile mic that you can buy for the most reasonable price has already been mentioned. The Audio Technica AT822 which cmes with a street price of around $250. It comes with the necessary adapter (XLRF to mini) and will plug directly into the camera. Just set the switch to "mic" instead of "line". If you need to extend it just buy a regular XLR cable of the length you need and extend it. If you want to mount it to the camera the mike comes with an adapter for that. The only thing you can't do with that mic easily is connect it to a mixer. For that you have to construct a special cable (which I did) so I could split the left and right outputs of the mike and control them independently with my mixer (Behringer MXB1002) as well. The output of the mixer is via a dual (left and right) 1/4" to XLR adapter (which also happened to come with the AT822) to an XLR standard cable of whatever length I need to the XLR to mini adapter (that came with the AT822) into the camera. Only in that case you switch it to "line" because it is coming from a mixer. I have done entire stage productions with NO NOISE using this setup.

I also have an XLR Pro, but I hardly ever use it for that camera. I find that device more useful for my Hi8 camera.

John

If you need the wiring diagram for the special cable I constructed for the AT822 in order to connect it to a mixer let me know and I'll send you the graphic I made.
mhbstevens wrote on 2/8/2005, 11:38 AM
The AR822 is a great mic and great looking too and DOES have the right lead but I do not want a stereo mic for interviews / voice-overs. I don't find a mono equivalent. The nearest is the ATR55 shotgun but this is not a great mic. Guess I may need an XLR mic with a transformer. As far as the cabel recommended by Spot I have only found a "XLR to 1/4" phone" nothing to 1/8th or 3.5mm min-plu as on the FX1.

Mike

filmy wrote on 2/8/2005, 12:27 PM
>>>As far as the cabel recommended by Spot I have only found a "XLR to 1/4" phone" nothing to 1/8th or 3.5mm min-plu as on the FX1.<<<

Not sure if you read my post or not - The Shure A97f that I mentioned is XLR to mini and would work fine. The link is too the "manual" in PDF format.
mhbstevens wrote on 2/8/2005, 12:38 PM
I did read your link and I like the Shure adapter and may well get it, but Spot was talking of a cable and transformer all in one. he called it an XLR to min-plug cabel.

Thanks
filmy wrote on 2/8/2005, 12:47 PM
>>>...Spot was talking of a cable and transformer all in one.<<<

Unless i am misunderstanding what Spot and you are talking about when you say "transformer" the A97F is just that -

This transformer matches low-impedance microphones to medium-impedance inputs (found in many cassette and reel-to reel tape recorders). The low-impedance end of the A97F matches microphones rated at 150 or 600 Ω; the mediumimpedance end matches inputs rated at 3,000 Ω (1,000 to 7,000 Ω actual impedance).

(And this is a mono adapter)
riredale wrote on 2/8/2005, 2:27 PM
MHBstevens:

If you want mono, couldn't you just take the Stereo AT822 and combine both L and R channels during editing? Since the microphone capsules are immediately adjacent to each other, I would think you'd get a high quality mono mix.

There might be some way to combine L and R electrically and just record the resulting mono signal, but I don't remember where I saw such a diagram for the at822.

In this way you also get a very decent stereo microphone thown in for free for those times you want an ambient stereo sound.
mhbstevens wrote on 2/8/2005, 5:54 PM
True but it is silly to pay more for a stereo mic when there are great mono stick mics at half the cost.
B.Verlik wrote on 2/8/2005, 6:48 PM
You'll probably have to search pretty good to find these, but I use to buy XLR transformers, similar to switchcraft or HOSA, that had a slider switch to choose either Hi or Lo impedence, and a 6 inch cable with a 1/4 inch male (guitar like) plug. They use to sell for $ 14.95 and were a rare find, but I liked them because I used a 4 track with 1/4 inch inputs and the 6 inch cable wouldn't stress the input jacks of the recorder and allowed me to record in Lo impedence into the input of the recorder. It would be SO easy to solder a 3.5 inch plug in place of the 1/4 inch plug. I looked a little, but couldn't find any, yet.
Spot|DSE wrote on 2/8/2005, 6:53 PM
The XLR to miniplug with the transformer built in are very hard to find, so I've been building my own by putting a mini on a standard cable, replacing the normal TRS plug that's found on there.
Somewhere in this thread, I lost what you were trying to achieve. If you have a stereo mic, you'll need dual transformers, one for each channel. At this stage, I'd recommend using a BeachTek or Studio Devices box, or something similar because you'll end up with a large mass. You could also (more easily) order a plug from AT or Hosa that has the 825 connector on female side and 2 mono 1/8 on the other. Then use a headphone style splitter to get these two mono connections into your cam as a stereo signal.
I hope I understood where you are going?
craftech wrote on 2/8/2005, 7:22 PM
The FX1 is a top end camera so I am wondering what did Sony see me buying for street interviews or did they expect me to add a XLR mixer box at the camera like I was trying to avoid?
==========
I think what you fail to realize is that the FX1 is a consumer camera like the VX2000 and the VX2100 were. It is not packaged as a pro camera. Virtually all consumer cams have 3.5 stereo mic inputs, NOT XLR inputs. The pro versions of these cameras come with those. That is not to say that any of those cameras can't hold their own with the pro versions, but for whatever reason, Sony chose to package the FX1 the same way they package any of their other high end "consumer" cams.
If you look at any microphone solutions people have found for the VX2000 or VX2100 they will also work on the FX1 because the mic inouts are all the same.

John
craftech wrote on 2/8/2005, 7:41 PM
One thing I was wondering about that cam and other HD semi-professional cams was that if they are using Mpeg compression on the audio when they record (which I understand they all are) how can one accurately evaluate and test the audio performance when to my knowledge there are no objective tests that can factor in that type of compression.

John
mhbstevens wrote on 2/9/2005, 8:00 AM
OK: So we can put this to bed - call it a wrap - I'm ordering the ElectroVoice 635A stick mic with the Shure A96F to take it into the 1/8th" mini-plug on the FX1.

Thanks for all your help.