# I need help building a crossover

Discussion in 'Electronic Basics' started by Ryan Richards \(Diesel Breath\), Jun 21, 2004.

1. ### Ryan Richards \(Diesel Breath\)Guest

I need to make a crossover.. nothing fancy or anything... I remember in
college we went over how to make a crossover and I think it had something to
do with a resistor and a capacitor... Anyway, here's what I'm trying to
accomplish...

I have a bass rig and the cab only goes up to 5kHz... I have a component
system; meaning I have a preamp and a separate power amp... I want to insert
the crossover between the pre and the power so the power amp isn't wasting
its time with frequencies that the cab doesn't even support... I need it to
crossover at 5kHz and slope at 18dB/oct... Any help is good help... thanks
again

2. ### JeffMGuest

Posting the same question independently to multiple groups
is not the prefered method.

This practice
robs those people who do not habitually visit all the groups
of the wisdom of others on the topic.
It also doesn't let everyone know
when the question has been answered sufficiently.

If the query is relevant to multiple groups,
DO cross-post (within reason).
Proper use of the Followup-To line is also useful.

3. ### Bob MastaGuest

It sounds like all you need is a simple low-pass filter,
and maybe not even that. I'd guess that with a normal
bass, there would be little enough energy above 5 kHz
to begin with. However, if you are using effects like
fuzz, there might indeed be a lot of extra harmonic
energy. I don't know how serious this would be for the
amp, but it might sound too gritty for your preferences.
I would have thought that the preamp had tone controls
that would accomplish this nicely, but if that is home-built
or otherwise without them, try adding just about any
simple low-pass filter. I assume that the 5 kHz limit
is in the speaker itself, not the power amp, otherwise
don't bother. Start off with a simple passive R-C filter
between the preamp and amp. You'll need to determine
the impedance of the amp and include it in the calculations
for a proper design, but you will probably be well served to
just do it by ear: Increase the R or C until you hear some
loss in the high end with the fuzz active, and adjust to taste.

The cutoff frequency is 1 / (2 * pi * R * C), where R is in ohms
and C is in Farads. So for example with a 0.01 uFd cap, you
would solve for R = 1 / (2 * pi * 5000 * 0.01x10^-6) = 3180 ohms.
Use the nearest value you have on hand.

Hope this helps!

Bob Masta