variable gain amplifier using analog optoisolators
Posted: Mon Nov 23, 2020 11:30 am
I´m Horst from Bavaria, been lurking for some time.
My current project is an optical dynamics processor to manage my audio, the main goal is to prevent the level going higher than 0 dBu.
I purchased the fastest optos available, the Tesla 3WK160 which has an almost zero attack and release.
By biasing the LEDs and trimming the on resistance I managed to get a total gain range of 40 dB. Left-right balance isn´t perfect yet but usable.
The control signal from the input feeds a fixed threshold gate/expander circuit. While this already works quite well, the limiter which gets its control signal from the output produces some heavy artifacts. Despite being a beginner I know why this is happening but not how to get rid of it. A friend recommended to set attack and release to 10 ms or higher. This reduces the audible distortions but introduces a lag which prevents the limiter circuit to react in time. As already mentioned, I need a consistent level of 0 dBu at the output.
My question is how to design a sidechain which gives a smooth response yet fast enough to catch those nasty peaks ?
My current project is an optical dynamics processor to manage my audio, the main goal is to prevent the level going higher than 0 dBu.
I purchased the fastest optos available, the Tesla 3WK160 which has an almost zero attack and release.
By biasing the LEDs and trimming the on resistance I managed to get a total gain range of 40 dB. Left-right balance isn´t perfect yet but usable.
The control signal from the input feeds a fixed threshold gate/expander circuit. While this already works quite well, the limiter which gets its control signal from the output produces some heavy artifacts. Despite being a beginner I know why this is happening but not how to get rid of it. A friend recommended to set attack and release to 10 ms or higher. This reduces the audible distortions but introduces a lag which prevents the limiter circuit to react in time. As already mentioned, I need a consistent level of 0 dBu at the output.
My question is how to design a sidechain which gives a smooth response yet fast enough to catch those nasty peaks ?