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Old July 18th, 2004, 11:43 AM   #1
Fred Retread
 
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Okay, Physics enthusiasts...

I'm about to invest in some sound uprgrades for my GL2. I'll be asking for some practical advice pertaining to what I intend to shoot, but I'm kind of a gearhead, so I like to start by understanding as much as I can at the tech level.

I wanted to know what the nominal input impedance of the GL2's minijack mic terminal input is. The specs from the GL2 manual only give this about that input:

" -35dBV (with 600 ohm mic)/5.6kohms (MIC ATT ON)
-55dBV (with 600 ohm mic)/5.6 kohms (MIC ATT OFF) "

I have an electronics background, but that spec just doesn't speak to me. If the input impedance is implicit in that spec I'm not getting it. First, can someone tell me what the " /5600 ohms " is supposed to indicate?

Second, I believe that dBV is the decibel level with respect to one volt, so -35dBV would be 178 mili volts. It that's true I can't discern what this spec is trying to tell me.

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Old July 18th, 2004, 12:51 PM   #2
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Others can speak more accurately to the impedence issues, but from a practical standpoint the -35/-55 level indicates the power of the mic signal that is expected at the input.
Take a look at some mic specs on manufacturer's websites. You'll see that range fits in with most mics sensitivity rating.
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Old July 18th, 2004, 07:37 PM   #3
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Making progress ...

Thanks, Jay. That makes sense in context , i.e., the GL2 expects a greater input signal if attenuation is on. I'm currently assuming that the " / " does not indicate division, and that 5.6 kiloohms is the nominal imput impedance. What's still bothering me is whether those signal levels are minimum or nominal. I've written an email inquiry to Canon.

I also took your advice and went to Sennheiser's , Azden's and Audio-Technica's sites to look at microphones commonly mentioned here (ME66, MKE300, SGM-1X, AT897).

The sensitivity and impedance specs square with the comparative results that Jeff Toogood, for example, got with the ME66 v. the SGM-1X (see his recent post on this board). The ME66 is "hot" as people say because it puts out 50 mV per Pascal of air pressure variation, compared to, say, the SGM's 8.9 mV per Pascal. Plus, with its 680 ohm impedance going into Jeff's MA300 (assuming the XLR imputs are 200 ohm like Beachtek's are) the SGM-1X's output gets 13 dB of attentuation where the ME66 with its 200 impedance only gets 6dB attenuation. If the MA300 does indeed have an input impedance of 200 ohms (Canon doesn't say) then the SGM would fare better signal strength-wise if it were used with an XLR to minijack adaptor and plugged directly into the GL2 5.6 kohm jack. That's the kind of analysis I like to be able to do before buying stuff.

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Old July 18th, 2004, 09:49 PM   #4
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Correction


I previously wrote:
>>...assuming the [MA300's] XLR imputs are 200 ohm like Beachtek's are...>>

I don't know where I got the notion that Beachtek adaptors have 200 ohm XLR imputs. Their site says they're compatable with 150-600 ohm mics, and B&H list their imput impedance at 600 ohms. I think I crammed too much reading into too short a period, some of it consisting of web articles that may lack accuracy, and then started shooting my mouth off before I digested it all. I hate it when that happens.
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Old July 18th, 2004, 10:01 PM   #5
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My understanding is that those levels are nominal.

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Old July 19th, 2004, 12:07 AM   #6
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Stop reading so much into the specification., if you take a good look at the Azden site the specs are pretty well meaningless. Use your ears, it's the only way to fly.

You're going to upgrade. What would you like to do?

Ideally you want impedance matching and a balanced XLR input for a quality mic. 48 volt phantom, preamplification and limiters would open up great potential

If you want to start slowly get a decent battery powered mic and an XLR to 3.5 (1/8")adapter ($10)

If you buy a Beach with 48 volt pantom, that's arounf $270. Go the extra and buy the DXA-8. That way you could use mics like the Oktava .
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