How to buffer a sallen-key circuit

Hello Dears,

I am try to go active on the bass with a II order active crossover with a Linkwitz-Riley slope (Q=0.5) as the one described here:

Active Filters

the II order xover should fit in my design pretty well based on calculations and measurements. While I want the highpass at fixed output, I would like to have the low pass adjustable.

The real problem to is how to buffer it.

Input buffer: my tube preamp needs at least 100KOhms load to really sing, and this spec is fully accomplished by my amp at the moment. Somebody suggested to used a a simple cathode follower tube buffer and to place the xover near the preamp.

Output buffer: the ideal situation would be to have an output which makes possible to adjustments in the range of +/- 3dB, so an output buffer and a volume pot is needed. Could you suggest some circuit that can do this.

Best Wishes
Two way, buffered before and after
Cheers George


  • 2 way schematic jpeg.JPG
    2 way schematic jpeg.JPG
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