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MCI JH-24 VU meter calibration
Old 4 weeks ago
Gear Addict
AnalogBrain's Avatar

MCI JH-24 VU meter calibration

Hey guys,

I've calibrated dozens of machines over the years, mostly Studers and Otaris.
While I have calibrated a few MCI machines, I have never calibrated the in/out.

I am helping a friend get his new JH24 up and running.

I have been adjusting the "IN CAL" pot for an accurate in/out of 1K. My Oscillator puts out 4dB @ 1K, and the multimeter reads 4dB @ 1K on the machine output. Pretty standard stuff.

I then tweak the VU meter to read 0VU by adjusting the pot on the meter buffer board. For all of the channels, I have only needed to barely adjust the VU to get it right at 0VU.

There are two channels where the VU meter is like 8-10dB off from the multimeter. When I adjust the pot on the VU buffer board, the output of the machine changes drastically as if the VU is adjusting the input (or output) gain.

Could anyone shed some light on this?

Thanks so much!!!
Old 4 weeks ago
Lives for gear
Radardoug's Avatar

Have the boards been modified? Do you have a schematic? Maybe the cal pot is right on the input, and is miswired so it shorts the line out.
Old 4 weeks ago
Lives for gear
bad adjustment pot?
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