Silvas
Well-known member
Hello
I´ve had many requests for the variable scale meter board i used with my GSSL compressors :
So, here is it, not the nicest layout, but it worked for me. I´m still learning Eagle...
Component layout here :
http://i523.photobucket.com/albums/w355/audioeng80/VARIABLESCALEMETERCOMPONENTS.jpg
Copper side, ready to print and transfer :
http://i523.photobucket.com/albums/w355/audioeng80/VARIABLESCALEMETERFORHOMEETCHING.jpg
Size is 100x60mm. Led spacing is 10mm
It needs a 3pos rotary switch. I used 10pos 36 degree index with programmable stops grayhills in my GSSL builds.
IIRC, the way i calibrate the board is :
1 - Before i solder the GR calibratin trimmers (20, 10 and 5 dB) i adjust them to the following values : 20dB : 1.05k, 10dB : 3.16k , 5dB : 7.32k. The 4th trimmer, which is used to set the led current , i left it at half of it´s value. I think i used 10k trimmers except the 4th trimmer.
2 - assuming that the GSSL is working, i feed voltages to the board, but measuring current draw with my DMM on the positive rail, and without the TL071 opamp on the socket. Then, i feed a positive voltage to the input pin on LM3914, pin 5. High enough to make all the leds on. The bar/dot jumper should be in.
3- i adjust the 4th trimmer for 70mA current draw with all leds on.
4- i put the opamp in place. Then i feed the compressor with a 0dBFS tone and i monitor levels on Protools (or your DAW of choice). Threshold should be fully CW and no compression should be happening.
5- I put the meter scale on the 20dB position, and adjust threshold for a measured 20dB GR, bypassing the compressor and checking the levels in DAW. Should be exactly 20dB difference with the compressor working.
6 - Adjust the first trimmer so the last led is barely glowing ! Adjust threshold for a measured 10dB GR on DAW, then check that the meter is reading 10dB, the 5th led. If not, adjust the trimmer and check again until reading is OK.
7 - repeat the process with trimmers 2 & 3, with the rotary on it´s respective positions, and adjusting the threshold for a 10dB and 5dB gain reduction....
I´ve found this meter is very accurate, specially in the 5dB position (0,5dB accuracy) and i love having all the 3 scales for different tasks. I prefer bar mode, is easier to read, but i left the option for dot mode. Excuse me if the explanation is not so clear, my english isn´t the best.
I´ve had many requests for the variable scale meter board i used with my GSSL compressors :
So, here is it, not the nicest layout, but it worked for me. I´m still learning Eagle...
Component layout here :
http://i523.photobucket.com/albums/w355/audioeng80/VARIABLESCALEMETERCOMPONENTS.jpg
Copper side, ready to print and transfer :
http://i523.photobucket.com/albums/w355/audioeng80/VARIABLESCALEMETERFORHOMEETCHING.jpg
Size is 100x60mm. Led spacing is 10mm
It needs a 3pos rotary switch. I used 10pos 36 degree index with programmable stops grayhills in my GSSL builds.
IIRC, the way i calibrate the board is :
1 - Before i solder the GR calibratin trimmers (20, 10 and 5 dB) i adjust them to the following values : 20dB : 1.05k, 10dB : 3.16k , 5dB : 7.32k. The 4th trimmer, which is used to set the led current , i left it at half of it´s value. I think i used 10k trimmers except the 4th trimmer.
2 - assuming that the GSSL is working, i feed voltages to the board, but measuring current draw with my DMM on the positive rail, and without the TL071 opamp on the socket. Then, i feed a positive voltage to the input pin on LM3914, pin 5. High enough to make all the leds on. The bar/dot jumper should be in.
3- i adjust the 4th trimmer for 70mA current draw with all leds on.
4- i put the opamp in place. Then i feed the compressor with a 0dBFS tone and i monitor levels on Protools (or your DAW of choice). Threshold should be fully CW and no compression should be happening.
5- I put the meter scale on the 20dB position, and adjust threshold for a measured 20dB GR, bypassing the compressor and checking the levels in DAW. Should be exactly 20dB difference with the compressor working.
6 - Adjust the first trimmer so the last led is barely glowing ! Adjust threshold for a measured 10dB GR on DAW, then check that the meter is reading 10dB, the 5th led. If not, adjust the trimmer and check again until reading is OK.
7 - repeat the process with trimmers 2 & 3, with the rotary on it´s respective positions, and adjusting the threshold for a 10dB and 5dB gain reduction....
I´ve found this meter is very accurate, specially in the 5dB position (0,5dB accuracy) and i love having all the 3 scales for different tasks. I prefer bar mode, is easier to read, but i left the option for dot mode. Excuse me if the explanation is not so clear, my english isn´t the best.