Bass-Booster for Headphones
Background
So, Im about to build my own headphones. And one thing that I want in the headphones is a deep base. Therefore I have done one prototype board with just a BassBooster, and I thought that Ill sheer It with all you that is in the need for one.
You can also by one from me if you want. Contact me her and we’ll discuss price and shipping.
Theory
The base, (bass) in the music and sounds are the low frequency sound waves. In most cases it is in the range of 10Hz-200Hz, There are more to it than this, but lets keep things simple.
Now, I want to gain alla the frequency from 0-200Hz. In this project I want to Gain the signal, not just filter out the low frequency keys, one can combine the standard filter and Operational Amplifier to gain the signal. But there are better designs to do it. By using a Sallen-Key filter the combination of filter and Gain is done in the design. (Note that the values for the standard filter are not valide in the the Sallen-key case)
Due to the fact that one dose not know the AC ripple (or bös as we call it in Sweden) out from the source. Often a high pass filter is added before the main filter and gain.
[Bild High Pass filter]
The Cutoff Frequency is set to 15Hz, du to the fact that we want the low free-signals to pass through.
[Bild Salen Key]
The values that is used to drive a fc at 200Hz are
R1 = 8.2kΩ
R2 = 8.2kΩ
C1 = 0.1uF
C2 = 0.1uF
Shematic
Here is the shematic of my bass booster (OBS!, only for one channel, if you want stereo you need to copy it ) note that there are several more Operational amp, this due to the fact that I amplify the signal in two parallell steps, one is to increase the bass, and the other one is to suppress, all other signals that is over the bass region.
The first amp in each line is for buffering, second is the Salenkey configuration. The las one that merge the two separate lines, this is to make sure that the two signals merges together at the right time, (so that the bass don’t have a delay)
PCB
Here is the PSC layout, with an standard audio plugg input and output. The two potentiometers are used for trimming in the Bass and the Middle register, you can then see this as a 2 channel equlizer.
