Here is my initial prototype build of a LED level meter design, with a few fudges made to the PCB which have since been included into the second board iteration.
I wanted to make a meter that is not in anyway average or quasi-peak responding to audio-frequency signals and that has a dynamic range sufficient to indicate the noise floor of a signal source.
As far as audio frequency signals are concerned, the unit has practically zero attack or integration time. It will accurately indicate the peak amplitude of one single half-cycle of a 20kHz sine wave of either polarity.
As for the dynamic range, there are 48 LEDs at 2dB intervals. The most significant yellow LED is the 0dB indicator, calibrated to +4dBu (professional line level - 1.736V peak). The least significant LED is activated by a few tens of uV.
The decay rate is adjustable via the potentiometer from very fast to very slow, so you can have either a dynamic display visually dancing to the music or one capturing and holding the peaks.
The audio input is balanced with a high CMRR for ground loop hum rejection.
The achieved dynamic range and true peak reading response couldn't have been done along the lines of traditional techniques using active rectifier and peak detection circuitry, so there is none of that whatsoever in the design.
The input signal, split into three separate gain groups, is fed directly to level comparators and the LED driving and decay is handled after the comparators digitally.
The PCB is designed with a low profile for stacking. I am currently designing a 1U rack panel in CAD (Front Panel Designer) for inclusion into my audio system which will sport a stereo pair.
Most of the parts are dirt-cheap garden variety sorts, except for the Analog Devices op-amps in the low-noise/drift signal section which are quite pricey.
I'll eventually publish the design and post the Gerber files when I've finished writing it up.
I wanted to make a meter that is not in anyway average or quasi-peak responding to audio-frequency signals and that has a dynamic range sufficient to indicate the noise floor of a signal source.
As far as audio frequency signals are concerned, the unit has practically zero attack or integration time. It will accurately indicate the peak amplitude of one single half-cycle of a 20kHz sine wave of either polarity.
As for the dynamic range, there are 48 LEDs at 2dB intervals. The most significant yellow LED is the 0dB indicator, calibrated to +4dBu (professional line level - 1.736V peak). The least significant LED is activated by a few tens of uV.
The decay rate is adjustable via the potentiometer from very fast to very slow, so you can have either a dynamic display visually dancing to the music or one capturing and holding the peaks.
The audio input is balanced with a high CMRR for ground loop hum rejection.
The achieved dynamic range and true peak reading response couldn't have been done along the lines of traditional techniques using active rectifier and peak detection circuitry, so there is none of that whatsoever in the design.
The input signal, split into three separate gain groups, is fed directly to level comparators and the LED driving and decay is handled after the comparators digitally.
The PCB is designed with a low profile for stacking. I am currently designing a 1U rack panel in CAD (Front Panel Designer) for inclusion into my audio system which will sport a stereo pair.
Most of the parts are dirt-cheap garden variety sorts, except for the Analog Devices op-amps in the low-noise/drift signal section which are quite pricey.
I'll eventually publish the design and post the Gerber files when I've finished writing it up.
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