Roof for frecuencys in a OD (Ts like)...

[richon]

Hello,

I was looking at some info of the roof of High frecuency to know how much highs to cut from a TS-like Feedback loop Opamp in a OD.

51pf is the value of the TS, the OCD is 220pf.... 

Is it safe to cut from 3KHz?... or should it be a little higher for it to sound very clear and not to dark??

[Mark Hammer]

How high/low is also a function of how steep.  A single pole of filtering, whether a feedback cap or a treble-bleed cap, only provides for reducing treble content by 6db/oct.  So, if the rolloff starts at a nominal 6khz, any remaining treble is only 6db lower in amplitude at at 12khz.  There are several strategies one can adopt.  One is to move the rolloff lower down so as to achieve the desired reduction at designated higher frequencies.  The other strategy is to use multiple poles of filtering so as to produce a steeper rolloff.

For example, if I have a 6db/oct rolloff starting at 3khz, at 12khz, content is reduced by 12db.  If I have an 18db/oct rolloff starting at 6khz, then content at 12khz is 18db lower.  So, the filtering may start higher up, but because of its selectivity, it actually removes more of the offending content.