Last time I have a blog post regarding on how to control the LC75341 tone control using arduino. I never really tested the performance of that IC until recently I got time to play with it. My initial impression was not good. The bass sound seems very thin and I can’t get the “boomy bass” sound that I wanted. Maybe its just me but the bass sound is thin compared to my little JBL flip bluetooth speaker. By the the way, the kit was from E-Gizmo’s digitally controlled tone control. I have investigated and model the circuit of the LC75341 tone control for simulation and the simulation results confirm what I am hearing.
The band width of the bass boost was very narrow that it will only cover very narrow frequencies of bass sounds. The values of the RC of the e-gizmo kit is different from the datasheet values. The e-gizmo kit has lower center frequency of around 40Hz while the datasheet suggested values has a center frequency of around 100Hz.
Above is the frequency response of e-gizmo kit, datasheet values and modified values from me. I managed to increase the bandwidth of the bass by playing on the RC values of the bass filter.
Schematic
Below is the schematic of the E-Gizmo’s Digitally controlled tone control.
C12 and C11 are for treble frequency, if you want to have higher treble frequency, decrease their values.
C13-16, R1 and R2 are for bass frequency. The bass booster circuit is simply a bandpass filter. A bandpass filter is simply a combination of high pass filter(HPF) and low pass filter(LPF) in series. The problem on the design of this circuit is that the cut-off frequency of both HPF and LPF are the same, this is the reason why it has very narrow band of bass boost. This won’t give you a boomy bass sound! To fix this, you will need to make the bandwidth of the bandpass filter wider.
Simulation:
As always, I used simetrix to simulate my circuit. I have download link on my download page in case you want to download a copy of it. You can use it for free as long as it is for your personal use. The circuit model is obtained from the datasheet.
Here are the values used on my simulation:
Please take note that Part numbers on the schematic and simulation models are different. I am just lazy to edit it. haha! C9 and C10 is equal to the C5 on the simulation model. R1 and R2 is R2 on simulation. C13 and C14 is C2 on the simulation. C15 and C16 is C1 on simultion. C9 and C10 is C5 on sim.
E-Gizmo Model
R1, R2 = 3.7k
C13,C14 = 220n
C15,C16 = 220n
C9,C10 = 2.7n
Datasheet Model
R1, R2 = 3.7k
C13,C14 = 100n
C15,C16 = 100n
C9,C10 = 2.7n
My own Modified Model
R1, R2 = 10k
C13,C14 =1u
C15,C16 = 33n
C9,C10 = 1.5n
Simulation Result:
You can play with the simulation here: Downoad