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Old December 27th, 2005, 01:16 PM   #1
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balanced connection for mini-disk?

Is there anyone out there that could suggest a way of getting a balanced connection to mini-disk player.
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Old December 27th, 2005, 02:06 PM   #2
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Originally Posted by Greg Corke
Is there anyone out there that could suggest a way of getting a balanced connection to mini-disk player.
Assuming the mini-disc has a mic level input, how about with a Beachtec adapter like you'd use with a camera with only a miniplug mic input?
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Old December 27th, 2005, 03:26 PM   #3
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Thanks Steve

Hi Steve and thanks,

That might be a bit big. I know i asked you this question once before and you said that putting a straight xlr adapter onto the minidisk does not make it balanced. Sorry to sound dumb but why is that? Also, looking for lav mics for project. I was told the Sony ecm44 was pretty good what would you say. Additionaly do you know of anything similar that might be cheaper but do the same job (I chuckled to myself as I wrote that).

Thanks again for the input Greg C

P.S. I think I'm going to try the minidisk route. You said I may not have a problem with interference over that short distance i.e. from lav mic on actor to mini disk recorder on actor but I was wondering If you were to employ this method whether there is any tips you could give. Bearing in mind there is no sound mixer or boom op. (i.e. a crew of one).

Thanks again Greg
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Old December 28th, 2005, 07:18 AM   #4
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Quote:
Originally Posted by Greg Corke
Hi Steve and thanks,

That might be a bit big. I know i asked you this question once before and you said that putting a straight xlr adapter onto the minidisk does not make it balanced. Sorry to sound dumb but why is that? Also, looking for lav mics for project. I was told the Sony ecm44 was pretty good what would you say. Additionaly do you know of anything similar that might be cheaper but do the same job (I chuckled to myself as I wrote that).

Thanks again for the input Greg C

P.S. I think I'm going to try the minidisk route. You said I may not have a problem with interference over that short distance i.e. from lav mic on actor to mini disk recorder on actor but I was wondering If you were to employ this method whether there is any tips you could give. Bearing in mind there is no sound mixer or boom op. (i.e. a crew of one).

Thanks again Greg
Balanced connections use three conductors, "hot", "cold", and "neutral" or "ground." The neutral conductor is the cable shield. The signal is on the inner conductors with respect to ground - if you connect one side of a speaker to ONE of the inner wires and the other to "neutral" you'll hear the music. BUT the same signal is on BOTH inner conductors and they are fed 180 degrees out-of-phase with each other. If you were to connect a sensitive speaker to each inner conductor you'd hear nothing because the two cancel each other out. But any noise picked up in the cable will be picked up equally and in-phase by both wires. As a result you'd hear any interference flying around. Now when you connect it to a balanced input, the signal on the "cold" side is inverted in phase and combined with the signal on the "hot." That means that the desired signal is not cancelled any more but instead is reinforced. But the NOISE has also been inverted on the cold side and when it is mixed with the same but uninverted noise on hot, it is cancelled out.

Unbalanced connections don't do any of this inverting and mixing. An unbalnced cable just has two conductors - the inner wire and the outer shield. The signal appears between inner and shield. But if it picks up any noise on the way that is also there and there's nothing to cancel it out.

Why do simple adapters unbalance the whole thing? Because a connector adapter such as XLR to TS mono miniplug simply shorts out the XLR's "cold" pin to the shield. That half of the signal is lost and there's none of the noise cancelation that takes place in a balanced connection. If instead you try to use an XLR to TRS stereo miniplug, XLR hot goes to tip, XLR cold goes to ring, and XLR shield goes to shield. So the result is the same signal goes to both stereo right and left channels but the two are inverted in phase to each other. When you play it back on a stereo you get wierd effects (remember checking the speaker phase when you set up your stereo or home theatre?) and if you play it in mono, as the majority of videos end up being viewed, the two channels cancel each other and it's REALLY screwed up. Making it even more complicated when you use a simple adapter to plug into a camera or recorder, the camera's external mic connector might be acept a stereo miniplug but not a stereo signal, instead being mono on the tip with the ring being used for the low voltage bias power that some consumer mics require, especially those supplied as accessories with consumer video cams. The upshot of it all is if you want to send a balanced mic to an unbalanced input without losing the noise immunity of the balanced cable, you need an actual unbalancing circuit or transformer and that's where tools like the Beachtek come in (and the reason a simple cable adapter is $10 but a Beach is a couple hundred).

How would I do it? In descending order, I'd go with a wireless lav, a recorder that accepts a balanced mic such as the m-Audio Microtrack 2496, or an unbalanced mic for the minidisc like those from Giant Squid.
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Old December 28th, 2005, 09:17 AM   #5
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Quote:
Originally Posted by Steve House
...If you were to connect a sensitive speaker to each inner conductor you'd hear nothing because the two cancel each other out...
I fall into this trap all the time. I have a degree in this stuff, yet it's the simple pluses and minuses that trip me up. I had to think very carefully before writing this. Anyway, the speaker would produce the sound. At the source end electrons are being pulled from one conductor while being pushed into the other. So the same thing happens at the speaker.

Ground the center of both sides and nothing changes. No current flows from ground because the grounded points at both ends are at the same potential. The circuit is balanced. Noise in the form of voltage induced with the same polarity with respect to ground in both conductors is cancelled.

Move the ground to one end of the speaker coil and you short out half of the source. The other half still operates the speaker, but through the ground and with half the power. And now it's susceptible to induced noise.

Returning to the balanced cable, the two conductors do have opposite polarity with respect to ground. If a balanced signal is applied to the cam's stereo input, as happens often with the wrong XLR to mini adaptor cable, they are applied to separate left/right channel amplifiers and you'll have the opposite left/right signals that will cancel in weird ways when produced by stereo speakers as sound waves--wierd because where in space cancellation happens is a function of wavelength. Meanwhile, if they are mixed down to mono and applied to a mono speaker--including the cam's speaker--the result is no sound at all.
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Old December 28th, 2005, 10:04 AM   #6
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Quote:
Originally Posted by Fred Retread
I fall into this trap all the time. I have a degree in this stuff, yet it's the simple pluses and minuses that trip me up. I had to think very carefully before writing this. Anyway, the speaker would produce the sound. At the source end electrons are being pulled from one conductor while being pushed into the other. So the same thing happens at the speaker.
Of course you are correct - my bad - I was trying to illustrate the principle that the polaritys of the signals are opposite but equal and got sloppy in my "thought experiment." To actually get cancellation one would have to sum the signals, shorting hot and cold together and connecting the speaker between the junction and ground, rather than just connecting hot and cold in series through the speaker.

Rycote's Mic Info site has a good paper on the theory behind balanced feeds BTW.
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Old December 28th, 2005, 02:33 PM   #7
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Beachtech solution

I have a Beachtech adapter, and have done exactly what Steve suggested. It worked great. Of course this doesn't work if you are using it to record the bride and groom vows, or something like that, but it certainly will not work with boom mikes, set mikes, and off camera recording.

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Old December 29th, 2005, 02:26 PM   #8
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yes an improperly wired xlr-to mini cable will give you trouble, for the reasons explained above.

however, a $30 balanced to unbalanced TRANSFORMER, will keep the signal balanced up to the transformer, giving you an unbalanced signal only for the very short run (<1ft) between the transformer and md (or camera or whatever.) shure makes these and the model nos vary depending on the pysical connections, but the one you'd want is called something like the a95f or something. it'll do the trick, although it won't do anything about the fact that the mic pres in minidisc players are mediocre. a good portable mic pre that can put out a line level signal for your md would be preferable, but many times more expensive.
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Old December 29th, 2005, 02:56 PM   #9
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Originally Posted by Nate Ford
\
... it won't do anything about the fact that the mic pres in minidisc players are mediocre. a...
I'm only aware of one really professional grade minidisc recorder on the market today, the HHB Portadisc. Of course it's not pocket sized and at about $1400 it's not a cheap alternative to other types of recorders either.
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Old December 31st, 2005, 04:25 AM   #10
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Thanks

Hi Guys,

Thanks for the replies. I'm way out of my depth here but I can see your points. I think I might go for radios instead. I can just go straight into the camera then but I guess cost (and interference) is the big problem. seen a couple of possible sennheiser solutons (ew112p) any of you guys had any experince with these or know of anything comparable?

Thanks again for the enthusiastic and informative input.

All the best, Greg C.
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