Tone-Balance

Sub woofers are very popular, with home theatre being one of the driving forces. However, a good sub adds considerably to normal hi-fi program material, and especially so if it is predictable and has good response characteristics.The majority of sub woofers use a large speaker driver in a large box, with tuning vents and all the difficulties (and vagaries) that conventional operation entails. By conventional, I mean that the speaker and cabinet are operated as a resonant system, using the Thiele-Small parameters to obtain a box which will (if everything works as it should) provide excellent performance.

On this page three adjustable notch filters configurations are shown . They can be used in your small pre-amp or amplifier project to filter out any HUM at 50 Hz ( European ) or 60Hz . By sustituting the capacitors values in the bridge other frequencies can be used . All op-amps configuration requires a +/- voltage supply which can easily provided with a voltage divider made of two 100K resistors and a 10 uF filtering capacitor connected from ground to the negative rail . Any op-amps such as the LF353 , TL071, LM308 can be used and supply from a 9 volt battery or other voltage up to 30 volts can be used .

This audio bandpass filter is useful for amplification and filtering of weak AM TV video carriers. For example, a DFM (digital frequency audio multimeter) may have insufficient input sensitivity for measuring extremely weak SSB TV video audio signals. By using the 20 Hz filter to peak the wanted carrier, the DFM will display the carrier frequency. Another possible application for this filter is increased amplification and reduced bandwidth of weak BCB heterodyne AM carriers. The filter is also very useful for separating video carriers that are in close proximity of each other.

Although you can obtain universal, resistor-programmable switched -capacitor filters that are configurable as notch filters, most cannot operate at bandwidths higher than 100 kHz. Further, the typically 16- to 20-pin packages do not include a continuous -time, antialiasing filter to prevent spurious signals from appearing at the output. By using an eight-pin, dual operational amplifier and an eight-pin, switched-capacitor bandpass filter, you can construct a notch filter (Figure 1). IC2, a TLC082 is a dual BiCMOS op amp, replacing the older JFET-input stage with lower noise CMOS but retaining the bipolar output for high drive capability.

The adjustable lowpass filter is in a 3.625-in.-longΧ1.5-in.-wideΧ1.0625-in.-high Bud CU-123 die-cast aluminum box with input and output BNCs. Miniature toggle switches for the individual filter sections are accessible at the enclosure's exterior. Internal ground returns use solder lugs. The four filter sections have 50Ohm characteristic impedance and nominal 3-dB cutoff, from left to right in Figure 1, of 3.083, 6.586, 14.491, and 21.310 MHz. Table 1 shows the measured amplitude response for the box alone and for the four individual filter sections. The low-cost, adjustable lowpass filter delivers reasonable performance.

This simple tone control can be used in may audio applications. It can be added to amplifers, used as a stand alone control module, or even built into new and exciting instruments. It's one IC construction makes it a very compact circuit, as only a few support components are required. Plus, it does not use a dual power supply. This means that the circuit will run from 9V to 15V (although the bass will be a little weak at 9V). The circuit is by Robert Barg and originally appeared in the Think Tank column of the May 1998 issue of Popular Electronics..

The LM1036 is a DC controlled tone (bass/treble), volume and balance circuit for stereo applications in car radio, TV and audio systems. An additional control input allows loudness compensation to be simply effected. Four control inputs provide control of the bass, treble, balance and volume functions through application of DC voltages from a remote control system or, alternatively, from four potentiometers which may be biased from a zener regulated supply provided on the circuit. Each tone response is defined by a single capacitor chosen to give the desired characteristic.

The composite lowpass filter uses interior constant-k full sections terminated by m-derived half-sections.The design technique is also applicable to highpass and wideband filters (references 3 and 4). Figure 1 shows a schematic of the composite lowpass filter. The filter uses four inductors of two different values and five capacitors of two different values. Figure 2 shows the schematic of an equivalent composite lowpass filter. This filter uses judicious combinations of components in series, parallel, and series-parallel. The filter uses eight inductors and 14 capacitors of only one value each.

A variable notch filter with both high and low pass filters. At first glance this circuit looks fairly complex, but when broken down,can be divided into high pass and low pass filter sections followed by a summing amplifier with a gain of around 20 times. Supply rail voltage is +/- 9V DC. The controls may also be adjusted for use as a band stop (notch) filter or band pass filter.

This is an image Schematic. No Description available.

This is an image Schematic. No Description available.

The filter should provide adjustable gain to maximize SNR at the audio processor's first stage. The filter's frequency response should also include a notch at 19 kHz to achieve maximum attenuation at the FM-subcarrier pilot-tone frequency and thus minimize phasing problems. To reduce manufacturing costs, the filter should require no in-process adjustments. Conventional analog active-filter designs cannot meet these goals at reasonable cost and complexity without time-consuming adjustments. This Design Idea outlines an active-filter-synthesis approach that reduces a filter's sensitivity to passive-component tolerances and enables construction of inexpensive, high-order and highly selective filters.

You can use the circuit inFigure 2b to provide a digitally controlled tuning voltage to change the filter’s frequency response. The output of Figure 2b connects to the gain-control pins of IC1 and IC2 in Figure 2a. Figure 3a and b show the frequency response and group delay of the filter for various settings of VG. This level of performance strongly depends on proper layout, resistive terminations, and power-supply decoupling.

A common problem that arises when you design lowpass filters for signal conditioning is the filters' effect on the system's time-domain response. Because pushing the cutoff frequency lower slows the step response, the system may fail to recognize significant changes within a reasonable amount of time. The circuit in Figure 1 accommodates lower cutoff frequencies without sacrificing the step-response time. A window comparator monitors the delta (difference) between the filter's input and output. When the delta exceeds ±50 mV, the filter increases its slew rate by increasing the cutoff frequency by an order of magnitude. The switched-capacitor filter, IC1, normally operates as a self-clocked device.

The multiple feedback bandpass filter is a simple looking design, but it is difficult to calculate the values for a given set of parameters. These filters are useful for equalisation, analysis and other tasks such as the Sound to Light converter (Project 62) or even a fully functional Vocoder. For those who have not heard of the vocoder, it is a device that takes a music source as one input and vocals as the other, allowing a guitar, keyboard or complete ensemble to be made to speak or sing. The "speech" from a good vocoder is quite intelligible, and is "ear candy" of the very best kind for experimental musicians.

The LM1036 is a DC controlled tone (bass/treble), volume and balance circuit for stereo applications in car radio, TV and audio systems. An additional control input allows loudness compensation to be simply effected. Four control inputs provide control of the bass, treble, balance and volume functions through application of DC voltages from a remote control system or, alternatively, from four potentiometers which may be biased from a zener regulated supply provided on the circuit. Each tone response is defined by a single capacitor chosen to give the desired characteristic.

This preamplifier was designed as a stand-alone portable unit, useful to control the signals generated by guitar pick-ups, particularly the contact "bug" types applied to acoustic instruments. Obviously it can be used with any type of instrument and pick-up. It features a -10dB, 0dB and +10dB pre-set input selector to adjust input sensitivity, in order to cope with almost any pick-up type and model. A very long battery life is ensured by the incredibly low current consumption of this circuit, i.e. less than 800µA.

The three-amplifier implementation of the state-variable filter in Figure 1 provides for second-order bandpass, highpass, and lowpass responses. The strength of the circuit, however, is in the bandpass response (VOUT/VIN), in which it's easy to achieve high gain (G) and high Q. These two characteristics are important in applications in which selectivity is a key parameter in the filter. The application value of the circuit becomes even greater when DPPs (digitally programmable potentiometers) control and vary the bandpass filter's center frequency, f0, and passband gain, G.

Based on the classic Baxendall tone control circuit, this provides a maximum cut and boost of around 10dB at 10KHz and 50Hz. As the controls are passive, the first transistor, Q1, is configured as common - collector to act as a buffer stage. The last transistor, Q2, provides a slight boost. Note that the gain of the output of the Baxendall circuit is less than one because of passive nature of it. The output is designed to feed an amplifier with input impedance of 10kohms to 250kohms.

Designers originally conceived equal-element filters as all-pole microwave bandpass filters that provide minimum center-frequency insertion losses for specific values of resonator-unloaded Q (Reference 1). All resonators of the equal-element bandpass filter operate at the same loaded Q. For LC filters, the equal-element filter has another advantage. In the lowpass prototype, all inductors have the same value, and all capacitors have the same value. This minimum number of circuit elements provides design simplicity and reduces filter cost.