Electronic Crossover

The original design is from L.E. Larsen and has been published in L'Audiophile.

It's a Sallen Key type.
The basic formula for such a filter:

for a second order filter (12dB)

for a fourth order filter (24dB)

This is true for OP amps because they have a gain at 1, an infinite input impedance and an extremely low output impedance, but a tube cathode follower is not that close to an OP amp:

• The gain is not one, but more often 0.8-0.9
• The input impedance is lower
• The output impedance is much higher

As the formulas and explanations given in the article were particularly obscure, I don't give them here ...

Crossover 7KHz, 12dB

This schematic gives a 7KHz crossover frequency and slopes with a 12dB attenuation.

Crossover 5KHz, 24dB

This schematic gives a 5KHz crossover frequency and slopes with a 24dB attenuation.

Power Supply

This power supply is identical for both schematics.

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