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Author Topic: AKG C451EB 48V Mod?  (Read 239 times)

Spindrift

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AKG C451EB 48V Mod?
« on: March 30, 2019, 03:47:42 pm »

This post is related to the recent thread regarding snipping the jumper on the C414EB to lock it to 48V and ease the load on phantom supplies: 

https://repforums.prosoundweb.com/index.php/topic,37331.msg538131.html#msg538131

Does the AKG C451EB have a similar modification which can be performed which limits it to a 48V supply?  48V is the standard in phantom supplies in this day and age and I'm looking to lessen the load on my phantom supplies when employing these mics. I understand that the C452 was the strict 48V model but I'd like to not have to go hunting down more mic bodies.

Thanks,
Keith Banning
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David Satz

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Re: AKG C451EB 48V Mod?
« Reply #1 on: April 20, 2019, 04:10:43 pm »

I've been reluctant to reply to this posting because I don't have the specific information at hand. The C 451 was basically a 12-Volt microphone with protection to let it work safely with higher supply voltages as well. But when fed at 48 Volts it drew about 5.5 mA, back when the DIN standard prescribed only 2 mA per microphone.

The page shown below is from AKG's 1979 catalog. A few years after the C 451 was introduced, after problems and complaints arose, AKG introduced a variant model C 452 exclusively for 48-Volt phantom powering. It drew 3 mA--still greater than the value set by the DIN standard--but it brought fewer power supplies to their knees. I remember looking at its circuit and noting that it differed from the C 451 in the value of just one resistor.

Unfortunately I can't find the schematics right now, so I can't tell you which resistor to change to what value. But someone else here probably will know that--and if so, I hope that they'll post here in reply. The changeover can be made quite easily.

--best regards
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klaus

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Re: AKG C451EB 48V Mod?
« Reply #2 on: April 20, 2019, 10:52:08 pm »

In the 414EB, the conversion from 9-12VDC to 48VDC phantom powering is achieved by cutting a wire shorting bridge right at the line from the transformer center tap. This activates an 8.2kΩ resistor in series with the 330Ω resistor already present.

The 451also has the 330Ω resistor in the same position, but does not have the 8.2kΩ resistor option for phantom.

I am missing the parts supply sheet for the 452, but its schematic-identical with the 451- also shows one resistor in the same position as the 451's 330Ω resistor. I assume that resistor is an 8.2kΩ value, or thereabouts.

Conclusion: replace the 330Ω resistor in your 451 with an 8.2kΩ - 1/4 watt resistor, and your mic should be well suited for phantom supplies.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com
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