Cheers Albert!Albert H wrote: ↑Sun Feb 05, 2023 11:13 pm Here's the initial mods I did to the NRG Limiter to make it work properly in stereo. I added the left and right together to make the feed to the sidechain common, so there was only one sidechain needed. There were a couple of issues - the FETs had to be matched for pinch-off voltage, and it really needed an anti-overshoot clipper after it, with a further audio filter to shave off the upper harmonic clipping products.
We prototyped it, and it sounded great, but Stephen decided to go with two sidechains so that it could be separated (with minor modifications) for use as two separate mono limiters.
The circuit given below works well (with the above caveats), and I have a Veroboard layout that I did for the prototype and a PCB layout that I etched (by hand, as a one-off) - both worked well.
NRGlimmods+.png
You'll also notice that i used separate op-amps for each channel (NE5534) for the lowest noise and distortion. I also planned to replace the TL074 with an LM324, because it's a much cheaper part, and switches more slowly, making it much less likely to put switching noise into the audio as the LEDs light.
I also did a replacement op-amp based 15 kHz lowpass filter to replace the now unobtainable Toko Block Filter Modules.
I do like the release jumper which i should have added to the design? But i guess modifications could be done to the RC combinations if needed?
The Stereo expander is very interesting? I still do not understand fully how it works?