- [Narrator] It's time for a final challenge.
This is your chance to practice using
op-amp circuits as building blocks
to create more complicated devices.
For this challenge I need your help
to design an audio equalizer to use in my stereo.
An equalizer is an electronic device
that's used to adjust the balance of different
frequency components in an electrical signal.
They're commonly used in audio systems
to control how music will sound
when it's played on different speaker systems.
The equalizer consists of a bank of electronic filters.
Each filter has a different pass band
and the gain of each filter
can be individually controlled
to allow more or less of it's specific
frequency content through.
In a recording studio
it's not uncommon to encounter expensive
equalizer boards that have 30 or more
adjustable frequency bands.
On the other end of the spectrum
low cost equalizers,
like you might find on a car stereo,
usually have three frequency bands.
Labeled as bass, mid, and treble.
Although the exact frequency range for each band
will vary by device,
the base filter adjusts low frequencies.
Usually below 250 hertz.
The mid filter covers frequencies
from 250 hertz up to around two kilohertz
and the treble filter passes high frequencies
above two kilohertz.
For this challenge I'll keep things even simpler.
I want to create an equalizer circuit
with just two frequency bands.
The bass band should be used to adjust
the frequencies below 500 hertz
and the treble filter
will adjust all other frequencies above 500 hertz.
Your goal for this challenge
is to design an equalizer circuit
that can be used to manually adjust
the amount of bass and treble frequency content
within an audio signal.
The input signal for your equalizer
should be a single channel from an audio source,
such as an MP3 player.
Most audio players have two output channels
to produce stereo sound,
but for this challenge
you only need to worry about one of them.
So, pick your favorite side.
The output will be a single audio signal
containing the adjusted bass
and treble frequencies.
Your circuit will need to send the input signal
through two separate filters.
A low-pass filter
to isolate the bass frequencies
and a high-pass filter
to get just the treble frequencies.
Both of these filter should have a cut off frequency
of around 500 hertz.
Now for this challenge
that cut off point doesn't need to be exact.
As long as it's within plus or minus 50 hertz.
That's close enough.
The output from each of those filters
will then need to be combined back together
to create a single output signal
that can be played over a speaker.
Now,
this simplified block diagram
doesn't show where or how the gain for
each of these filer bands should be controlled
and I'm leaving that up to you
to figure out.
The only requirement for this challenge
is that the user can individually adjust
each bands gain.
It's up to you to decide how you want to
implement that capability
and what the minimum and maximum possible
gain values should be for each channel.
This is a complex challenge
with several different parts to consider.
I recommend using op-amp circuits
as building blocks that can be used to accomplish
different tasks within the larger design.
Once you decided the type of op-amp circuit
to use for each part of the design
you can then focus on each one individually
to figure out the specific part values
you'll need to use for it.
As one final tip
the output signal from your circuit
will probably not have enough power
to be directly connected to a speaker
and play loud enough to be heard.
So, to test your circuit
it might help to use a speaker system
with built in amplification.
Such as computer speakers,
which will let you listen to the output signal.
There are multiple solutions to this challenge.
So, take some time to think it through
and when you're done
be sure to watch my solution video
to see how I approach this problem.