Hi there,
I know what you mean: "An other SSL Bus comp topic" but this one should help a lot of us
I made some measure with REW on SSL Bus comp clone on the THD at 1KHz and at 100Hz.
Here is the result: (the comp is set like that: Threshold = -15dB, Ratio = 10, Attack = Fastest, Release = Fastest, Sidechain = OFF, MakeUp = 0dB, Turbo Mode = OFF)
1KHz THD measurement is 0.65% (think is huge)
100Hz THD measurement is 5.52% (Incredible Huge)
So i started checking all components, PSU values, Components way... Everything you can check i did.
And i found something interesting. The Full wave rectifier circuit doesn't work as good when frequency is low. The Voltage control is distorted when Frequency is low.
Both scope shows the voltage that control the VCAs at 1KHz and at 100Hz with the comp set like that: Threshold = -15dB, Ratio = 10, Attack = Fastest, Release = Fastest, Sidechain = OFF, MakeUp = 0dB, Turbo Mode = OFF)
Voltage control at 1KHz. DC looks quite flat and clean
Voltage control at 100Hz. DC looks distorted that is why we got to much 3rd harmonic
I'm thinking of a solution by using fast schottky diodes and a fast opamp and match input resistor perfectly
What do you think ?
Do you experiment with low frequency THD ?
