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Old June 30th, 2008, 09:48 PM   #1
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Anyone with SD 302 and a digital multimeter?

just got a new sound device 302 and testing the jacks with a fluke multimeter.

while all 3 inputs were nearly exactly 47.6v, the amperage was not constant.
input 1 and 3 were close near 30.5mA, but input 2 was only 28.5mA

anyone see the same levels on your 302?

thanks,



paul
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Old July 1st, 2008, 05:10 AM   #2
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Quote:
Originally Posted by Paul Chiu View Post
just got a new sound device 302 and testing the jacks with a fluke multimeter.

while all 3 inputs were nearly exactly 47.6v, the amperage was not constant.
input 1 and 3 were close near 30.5mA, but input 2 was only 28.5mA

anyone see the same levels on your 302?

thanks,



paul
You're verifying the phantom voltage? Remember voltage is measured ACROSS the source but current is measured IN SERIES with a load. If you're measuring with the meter across the XLR contacts, what you're seeing is an indication of a slight variation in the maximum current available from each input's phantom supply rails into the load presented by the meter's effective internal resistance (by Ohm's law ~1.6 kilohms). In actual use the current output is determined by the draw of the load applied. SD specs the available current at a minimum of ~10mA per input. Since most mics draw between 2 and 3 mA, you've got plenty of surplus capacity, which is all that really matters, and I wouldn't worry about it.
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Old July 1st, 2008, 06:10 AM   #3
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Steve,

I love it when you get all EE.:)

Regards,

Ty Ford
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Old July 1st, 2008, 06:47 AM   #4
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Watt you mean? I just try to stay on top of current developments. :)
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Old July 1st, 2008, 08:23 AM   #5
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All testing due to Schoeps mikes

thanks steve!

i was going through the motion since my sony xdcam-ex was not driving the schoeps shotgun with enough juice. the camcorder was measured to 6mA and with the schoeps at 32.9V. loadless at the nominal 47.8V

that 32.9V change got our concern, so we got a 302 for the mike.

with the schoeps connected, the leads also measured at 33.0V, but the 302 puts out well over the sony's 6mA, at those figures posted earlier.

i was just wondering about the variation between the 3 inputs jacks as the data difference seem too much.



Quote:
Originally Posted by Steve House View Post
You're verifying the phantom voltage? Remember voltage is measured ACROSS the source but current is measured IN SERIES with a load. If you're measuring with the meter across the XLR contacts, what you're seeing is an indication of a slight variation in the maximum current available from each input's phantom supply rails into the load presented by the meter's effective internal resistance (by Ohm's law ~1.6 kilohms). In actual use the current output is determined by the draw of the load applied. SD specs the available current at a minimum of ~10mA per input. Since most mics draw between 2 and 3 mA, you've got plenty of surplus capacity, which is all that really matters, and I wouldn't worry about it.
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Old July 1st, 2008, 08:39 AM   #6
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Rather than scatter the bones all over the floor here, call Sound Devices and ask them.

They are very approachable.

Regards,

Ty Ford
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Old July 1st, 2008, 09:35 AM   #7
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totally agree!

i placed a call already.
thanks ty

paul





Quote:
Originally Posted by Ty Ford View Post
Rather than scatter the bones all over the floor here, call Sound Devices and ask them.

They are very approachable.

Regards,

Ty Ford
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