R/E/P > Klaus Heyne's Mic Lab

Recommended Maximum NKMu Heater Voltage Output

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Ron Sweet:
How much of a heater voltage drop would you expect along a KM56 mic cable, compared to the heater voltage output of an NKMu power supply? What's a good maximum heater voltage as measured on the power supply output? If there's a reasonable answer, then I can avoid disassembling my KM56 to measure the heater voltage there. The NKMu schematic shows a heater voltage output of between 4 and 4.4 volts. Thanks for any insight.

klaus:
From experience: an original 10m Dörfler tube mic cable as was used by the broadcasters back then, would have a heater voltage drop of about 0.05-0.07VDC.

So if you set up your supply to put out exactly 4.00 VDC, you will be in the sweet spot for AC701 longevity and noise floor: 3.92-3.96VDC.

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