Active subwoofer filter circuit

This active subwoofer filter system provides the frequencies required to run the subwoofer within its limits. The purpose of this unit is to prevent the subwoofer speaker or circuit from overloading at unsupported frequencies. This approach can ensure the safety of the subwoofer speaker or driver circuit.

This system consists of TL074 based active lowpass filter, highpass filter, and preamplifier stage. The lowpass filter is in 880Hz cutoff frequency. Highpass filter cutoff frequency can select from the rotary switch. In this given design, the highpass cutting frequencies are at 80Hz, 115Hz, 150Hz, and 180Hz. Use the calculator application shown here to use this system for frequencies other than those mentioned above.

Finished prototype of an active subwoofer filter circuit.

In this circuit, both lowpass filter and high pass filter uses a 3-pole Butterworth filter configuration. Here all the filter component values are calculated using the calculator application mentioned above.

This circuit is useful to match the incompatible amplifier systems and subwoofer systems. Our primary test setup consists of few Yamaha active subwoofers and a Denon AVR system. Without this control circuit, we can see that the audio system produces loud noises at very low frequencies and puts a lot of pressure on the subwoofer speakers. After connecting this circuit, the problem disappeared, and the system generated a clean audio output.

Rear view of the active subwoofer filter circuit prototype.

To minimize the PCB size, we design this PCB using SMD components. Most of the resistors and capacitors used in this PCB are select from the 0603 packages. For the op-amp, we use a dual in-line package so that the user can easily change it without any soldering. The most common quad versions of the op-amps can use with this circuit, including TL074, TL084, TL064, LF347, etc.

This circuit is designed to power using a dual-rail 12V power supply. In our prototype, we used a 230V to 15V+15V, 15VA step-down transformer with this circuit.

All the soldering, mounting, and alignment procedure shows in the video attached to this article.

As mentioned above, at the testing stages, we create two versions of this circuit. The initial version consists of two 4558 op-amps and a highpass filter with a fixed cutoff frequency. The calculator application also builds around this design.

Version 2 of this filter circuit uses the same design, but we include a highpass cutoff frequency selector to this circuit and used a more convenient quad version of op-amp.

To adjust the GAIN control, apply 100Hz, 2Vpp, waveform into the audio input. Next, connect the oscilloscope to the output terminal and adjust the control. When making this adjustment, be sure to set the GAIN control to the location where the noise-free output will receive. The complete alignment process shows in the video attached to this article. According to our observations, keep this control in low or mid-gain positions for best results.

Internal view of the active subwoofer filter circuit prototype.

The RV2 provides to adjust the current going through the power indicator LED. For most of the LEDs, set this to a mid-position is sufficient.

This project is an open design. All the circuits and KiCAD design files are available to download here. The source code of the calculator application is also available at github.com.

CD2003 - yet another simple FM radio receiver

In the last few days, we are looking for some simple FM radio receiver to integrate into one of our ongoing projects. For that, we try several FM radio receiver ICs including TDA7000, CD2003/TA2003/TA8164, CXA1019, and KA22429. Out of all those chips we select CD2003 (or TA2003/TA8164) based receiver for our project because of its simplicity and outstanding performance. Except to CD2003, Sony CXA1019 also perform well but we drop it because of its higher component count. We design our receiver based on Toshiba TA2003 datasheet and later we try TA8164 and CD2003 with the same circuit. Either CD2003 or TA8164 can directly replace TA2003 IC, and as per our observations, TA8164 gives excellent results out of those 3 chips. A prototype version of CD2003 FM radio receiver The PCB design and schematic which we used in our prototype project are available to download at google drive (including pin-outs of crystal filters and inductors ). Except for CD2003 IC, this receiver consist...

Arduino superheterodyne receiver

In this project, we extend the shortwave superheterodyne receiver we developed a few years ago . Like the previous design, this receiver operates on the traditional superheterodyne principle. In this upgrade, we enhanced the local oscillator with Si5351 clock generator module and Arduino control circuit. Compared to the old design, this new receiver uses an improved version of an intermediate frequency amplifier with 3 I.F transformers. In this new design, we divide this receiver into several blocks, which include, mixer with a detector, a local oscillator, and an I.F amplifier. The I.F amplifier builds into one PCB. The filter stage, mixer, and detector stages place in another PCB. Prototype version of 455kHz I.F amplifier. In this prototype build, the Si5351 clock generator drives using an Arduino Uno board. With the given sketch, the user can tune and switch the shortwave meter bands using a rotary encoder. The supplied sketch support clock generation from 5205kHz (tuner f...

Experimental narrowband FM receiver for 2-meter band

This project is about MC3362 and ADF4351 based modularized, 2-meter narrow band FM receiver. In this design, the receiver splits into three modules as RF preamplifier, MC3362 tuner, and ADF4351 oscillator. The RF preamplifier builts around BF900 dual-gate MOSFET. The tuner stage builts using the popular MC3362 , low power narrowband FM receiver IC. For the oscillator, we use the ADF4351 DDS RF signal generator module. The core component of this receiver is MC3362 IC. This IC was designed by Motorola and is no longer in production, but this IC is still available to purchase in many online stores . The chip we used in this receiver was purchased from a local electronic component store for LKR 75 (USD 0.2). The RF preamplifier used in this receiver extracts from the N.Ganesan's (VU3GEK) LRR200, 2-meter band FM receiver project . Prototype version of the RF preamplifier. In this prototype, the above preamplifier was built as a module using a Manhattan construction technique. Th...

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