Graphic equalisers are a must in any good hi-fi systems! They enable you to shape the response of the system to the particular room, or in recordings to improve deficiencies of the equipment or the original recording. A good equalizer, used with skill can dramatically improve the quality of your listening pleasure.
This equalizer has five bands which cover all the audible frequencies, centred at 100, 320, 1,000, 3,500 and 10,000 Hz. The spacing between peak frequencies is two octaves which is quite adequate for most domestic applications. Frequency adjustment is 12dB/octave.
The circuit is for one channel and if you want to use it for STEREO you should build two, one for each channel of your system.
Technical Specifications – Characteristics
Working voltage: 6-15V DC
Frequency response: 20Hz-20KHz
Current: 60 ma
How it Works
This equaliser has five bands which cover all the audio frequencies, around 100, 320, 1,000, 3,500 and 10,000 Hz.
The circuit is for one channel and if you want to use it for STEREO you need two. The circuit consists of one LA3600 IC.
The circuit has been designed so that when the potentiometers are in the middle of their travel the signal is not affected at all. Turning a potentiometer in either direction will affect the corresponding frequency range accordingly. The maximum output voltage without distortion is 1 Vpp. The equaliser operates from a 12 VDC power supply which makes it suitable for use in home or car.
Construction
This work is not very difficult and if you stick to a few rules you should have no problems. The soldering iron that you use must be light and its power should not exceed the 25 Watts. The tip should be fine and must be kept clean at all times. For this purpose come very handy specially made sponges that are kept wet and from time to time you can wipe the hot tip on them to remove all the residues that tend to accumulate on it. The construction of the equaliser is very easy if you follow the diagrams and our advice carefully. The only really sensitive component are the IC. Start building the circuit by soldering the pins and the IC sockets in their places on the p.c. board. Solder then the resistors, the capacitors, making sure that the electrolytic are inserted the right way round before soldering them, and finally the potentiometers.
Depending on the size and the shape of the case you are going to use for the project you can either solder the potentiometers on the p.c. board directly or use short pieces of shielded audio cable to connect them with the rest of the circuit. When you have finished soldering the components on the board check everything for possible mistakes, clean the board with a solvent to remove all traces of soldering flux and insert the IC’s in their sockets. Make sure that you align them properly and that you do not bend their pins during insertion. Make then the following connections using shielded cable for the input and output and preferably twisted twin cable for the power supply.
- The supply (6-15 VDC recommend 12volt DC) must be connected at points 1 (+) and 2 (-) of the board.
- The input is at points 5 (signal) and 4 (earth).
- The output is at points 3 (signal) and 4 (earth).
If you turn the power on, and the potentiometers of the equaliser are in their middle position there shouldn’t be any notice able difference to the music if the equaliser is inserted or not in the signal path. However turning the potentiometers should produce a noticeable effect to the reproduction.
Parts
C1 = 2.2mF 22v
C2 = 47nF
C3 = 680nF
C4 = 15nF
C5 = 220nF
C6 = 4.7nF
C7 = 68nF
C8 = 1.2nF
C9 = 22nF
C10 = 470pF
C11 = 6.8nF
C12 = 1nF
C13 = 2.2mF
C14 = 100mF 22v
C15 = 100mF 22v
R1 = 4.7k
R2 = 10k
R3, 4, 5, 6, 7 = 100k Potentiometers
IC = LA3600 link
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