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Got a GR 1559-B Microphone Calibrator
Got a GR 1559-B Microphone Calibrator
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Old Today, 03:33 PM   #51
stijena1973 is offline stijena1973
diyAudio Member
Join Date: Nov 2012
Originally Posted by Conrad Hoffman View Post
Those are probably the same scans as on the jptronics site. If your B version is a later one, I'd love to see it.

I'm sure I can fix you up with some adapters. Email or PM me with what you need.

I'm getting stable results now and part of the secret is having a high impedance detector with low capacitance- the cable is important. That might be why they supplied a cable with the instrument. Use low C cable and keep it short. I even pondered putting a little FET buffer inside the XLR connector, but that's probably overkill.

I'm still not positive about the best way to calibrate the internal pots and position of the wiper/small knob. It's close, but I think better is possible. My present understanding is that achieving an accurate SPL requires that the attenuator produce an exact voltage. That seems to depend on the meter calibration, which depends on the PZT tube sensitivity. OTOH, that may be why they have three pots when two would have been enough for just the meter. Still thinking about it. Remember that all GR equipment was capable of better performance than the published specs. It wouldn't surprise me that with careful setup, this might be good to .1 or .2 dB.
PZT tube sensitivity is not a critical factor here. It is just one of the three microphones. Math takes care of any variation of its sensitivity.
Potenciometer also has some finite resolution, and also beginning of the scale , but that is all sub dB...
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