Vu Meter Scaling and Calibration

[mitchholtby]

Hi, I'm having a surprising amount of trouble after rebiasing a tube in my circuit. The 1ma meter was previously directly connected between the tube cathode and ground, measuring changes in current. Now with a new biasing, the changes in current no longer correctly correlate with the measured Db drop. So my gain reduction meter is completely inaccurate. I decided to buffer it regardless, but after that I'm looking for an easy scaling/calibration circuit if anyone knows of one. I see something similar in the 1176 schematic. Essentially I need to turn a drop from 1.7vdc to 1vdc at the input into a drop of 8db (more specifically 245mv to 94mv) at the output. I've simulated a ton of different log/antilog circuits and maybe it's something simple that's escaping me. Any help would be much appreciated! thanks!

 

[rock soderstrom]

Any help would be much appreciated! thanks!

Hi, the people here can help you much better if you tell us which compressor/limiter it is and what has been rebiased. A schematic will also improve your chances and maybe a few good photos...good luck.

 

[Neperdun]

It may be not so simple because the logarythm scale is used in the arrow VU indicator.
The cheapest and simplest way, I think, Is to connect it in parralel to sound card input, run any measuring software like SMAART and... go on!

 

[mitchholtby]

Hi, the people here can help you much better if you tell us which compressor/limiter it is and what has been rebiased. A schematic will also improve your chances and maybe a few good photos...good luck.

Thanks for your reply. It's a new varimu of my own design. Honestly the simplest solution is probably getting a different type of vu meter, but currently to translate the voltage from the tube into the voltage necessary on the meter follows this curve lol:


y = 0.00614957x^2 -.897851x + 98.6589

 

[mitchholtby]

It may be not so simple because the logarythm scale is used in the arrow VU indicator.
The cheapest and simplest way, I think, Is to connect it in parralel to sound card input, run any measuring software like SMAART and... go on!

Thanks for the reply! In the end I think I've decided to include a little microcontroller to run the function I listed in my last comment? There might be a better way but I couldn't find anything concrete with an opamp stage alone