The problem with the C 451 microphones was that at 48 Volts, they would draw nearly 6 mA apiece. If this caused the power supply voltage to sag, that was generally OK given the amplifier's design. But some supplies would collapse altogether, which was definitely not OK.
The C 452 differs from the C 451 by just one (higher) resistor value. The results are twofold: 48-Volt powering is required, and the current is limited to 3 mA per microphone. (AKG also offered a pair of large-diaphragm models--the C 414 EB and the C 414 EB P 48--having the "same difference" between them.)
Note that 3 mA per microphone was still a bit high for the time; the prevailing DIN standard still specified 2 mA as the maximum. Then Schoeps came along with transformerless microphones that drew about 4.5 mA in their 48-Volt incarnation. Within a few years Neumann introduced transformerless microphones of their own, which drew 2 to 3 mA or even a little more at startup. The DIN standard was revised to allow 10 mA per microphone, and that's where it stands today (DIN EN 61938). The short-circuit current of a standard 48 Volt phantom power circuit is about 14 mA per input, and the standard also recommends that phantom-powered equipment be able to tolerate such a short circuit without interruption to the remaining channels, which certainly seems like a good idea to me.
Due to the way this all developed, there are many phantom power supplies (and phantom-powered preamps and mixing desks) which don't have enough current available to power some of the better modern microphones properly. Unfortunately, it's not just older preamps and mixers that have this problem, so this still needs to be checked on a model-by-model basis. I have a good time at AES conventions going from booth to booth with a pair of Schoeps phantom power testers, seeing which recorders or mixers or preamps can light their LEDs and which ones can't ...
--best regards
Topic: akg c451 & c452 what's the diff? (Read 4970 times)