Hooking up Dorrough 40-A2 meters and calibrating levels?

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Hooking up Dorrough 40-A2 meters and calibrating levels?

Post by timpratt » Mon Sep 14, 2020 5:58 pm


I recently switched from a Crest Century 32ch mixing board to a Vintage Maker 32ch passive/active (Neuman v475-2c summing amp) analog summing box. It has three dedicated outputs before the master insert: A/B (switchable to either, but not both active at the same time), and C. C is what I want to use to send signal out to my newly acquired pair of Dorrough 40-A2 meters, however I also want to send that signal to my old Logitek Ultra-VU (to use the stereo phase correlation metering), as well as to my Gold Line Digital RTA. I am moving forward with using a Rolls RA163 distribution amp for this job. It has one stereo pair of xlr inputs that supply signal to four stereo xlr outputs. The specs of the Rolls are as follows:

Input Impedance: 100 K Ohms balanced
Max Input Level: +24 dBV
I/O Connectors: XLR
Output Impedance: 50 Ohms balanced
Max Output Level: +24 dB
Max Gain: 20 dB
S/N Ratio: >90 dB
Frequency Response: 10 Hz - 40 kHz, +/- 1 dB
THD: <.008%

This seems like a great solution to distribute my mix out to my metering gear. My question is, does this sound like the best option? I am hesitant about adding another gain stage for each output, but a passive transformer signal splitting solution will probably lose some gain with no option to make it up. Since the Rolls is something I already have, this seems like it will work and cost nothing to get everything up and going. What is the best way to calibrate the Dorrough meters with with the extra gain stage in the signal path? I'm assuming that I would generate test tone out of ProTools, send it to my analog summing mixer with its active summing amp making up for the loss of gain, then adjust the Rolls gain pot to match the signal ProTools is sending out. Does that seem correct? It seems too easy.
Tim Pratt

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