ACTIVE TWO WAY CROSSOVER - TWO WAY ELECTRONIC CROSSOVER
ACTIVE TWO WAY CROSSOVER -
TWO WAY ELECTRONIC CROSSOVER
The electronic crossover featured here is an 18dB / octave unit, and has the crossover frequency centered on 300Hz. The frequency may be changed by increasing (or decreasing) resistor / capacitor values.- Increasing capacitance or resistance - Reduces frequency
- Doubling the capacitance or resistance halves the frequency
- Reducing capacitance or resistance - Increases frequency
- Halving the capacitance or resistance doubles the frequency
The
values of resistance and capacitance (indicated with a * in the circuit
diagram) in the filter are critical, and close tolerance components are
mandatory. If you cannot obtain close tolerance capacitors, use a capacitance
meter to select values within 5% of the indicated value. Use only 1% metal film
resistors throughout. The 1uF coupling caps are not critical, and standard
tolerance is Ok.
If the crossover frequency is changed, it is
critical that the ratios of capacitor and resistor values are
not varied. For example, if you wanted to halve the frequency, the resistors
would become 22k and 102k (100k is only just acceptable. If the ratios are changed,
the filter damping is also changed, and the behaviour at the crossover point
will be unpredictable (causing a dip or peak in the frequency response).
The
values you change to alter the crossover frequency are indicated with a * in
the circuit diagram
Do
not change the 10k resistors - they set the damping of the filter and strange
happenings will befall s/he who fiddles indiscriminately.
CLICK ON THE IMAGE TO ENLARGE
Diagram shows the circuit diagram, and the NE5532 Dual op-amp is used. This circuit can
be operated from the same power supply as the Audio Preamp, featured elsewhere
on these pages. Other dual opamps may also be used, depending on your
preference.
Be careful when adjusting the level controls, since it is easy to create a mismatch in levels between the amplifiers. I suggest that the controls be mounted on the rear panel, with their shafts cut off really short, and a slot cut into the end with a hacksaw. Once the adjustment is made, it should not require further changes in use. Make sure that the power amplifier volume controls (if fitted) are turned fully up, and try to set the crossover controls so somewhere between midway and 75%. This ensures plenty of scope for getting the levels right, and will ensure that the preamp settings are not radically different from their "pre-biamp" days.
