I have just finished simulating the initial presence control design and it appears to work OK. We can get the same centre frequencies as the RS127 using the Carnhill VTB9044 inductor ( or the Chrion equivalent) and appropriate taps/caps. I have tweaked it so it has the same boost Q as indicated by the 4.7KHz curve in 'Recording The Beatles' (about 0.5). I am assuming the Q is the same at each of the four presence frequencies.
http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/presencesim.pngThe cut works using the same LC pairs as for boost and so, just like the Helios, the cut Q is several times the boost cut at about 2.5.
Now, I have no way of knowing if EMI use the same LC pairs for cut or a completely different set to keep the Q the same. In the absence of actual curves for the RS127 presence control it is impossible to know. So, does anyone have such a set of curves or could someone create them using the RS127 plug-in??
Cheers
Ian