This 10-channel equalizer with loudness feature operates with a ±12V DC symmetrical voltage. Current consumption is approximately 40mA. The slider potentiometers are rated at 100 kOhm with a 30mm stroke.
Input and output impedances are approximately 10 kOhm. The op-amp used in the audio input of the equalizer circuit is the NE5532.
The slider potentiometer section is located on a separate PCB. It’s a somewhat challenging and expensive project, but if you’re looking for nostalgia, it’s perfect for you 🙂
Author’s explanation:
I wanted to achieve “0 dB” at the output of the tone corrector so that the same reference value in terms of output voltage would be obtained across 10 octaves. Many of you may not know this, but most tone correctors without an integrated loudness option behave differently at 0 dB for a given frequency than at other frequencies.
In other words, to put it simply, for a tone corrector or equalizer without an integrated loudness option, if we say that 0 dB at 100 Hz means 100 mV, then 0 dB at 10 kHz might mean 330 mV, even though the tone adjustment at both frequencies can be within a +/-10 dB range.
When we initially set the high frequencies (10 kHz as an example) to, say, +10 dB, we are actually setting +10 + 10 = +20 dB (taking into account the ratio given by 330 mV / 100 mV and the gain in dB), and the attenuation is almost negligible compared to the 0 dB / 100 Hz reference.
This disadvantage of analog audio equalizers without high volume may not be noticeable in everyday listening, but it becomes annoying when we are trying to record an audio material or when we want the frequency response of an audio material to be as flat as possible at the output for later more precise processing, and for example: when we want +10 dB at high frequencies to be the same as +10 dB at low frequencies, in both cases the calculated dB must be relative to the same voltage reference.
One of the advantages of this audio equalizer project is the one described earlier. This, combined with the fact that the equalizer’s technical specifications are Hi-Fi and it is 10-octave focused, makes it ideal not only for the normalization of sound recordings on magnetic tape, but also for listening situations where the sound material is not properly recorded in terms of response to low, mid, and high frequencies.
10-Band Equalizer Circuit Diagram
source: tehnium-azi.ro/forums/topic/7615-dp0326-10-band-audio-equalizer-with-loudness/
