VU Meters

A high-resolution, average- (not peak-) reading volume-unit meter produces an accurate reading of loudness (Figure 1). The meter connects to the line outputs from the recording deck to monitor signal level. IC1A sums the left and right channels and adjusts gain. This adjustment allows you to calibrate the 0-dB LED, D1, to the signal level of your CD recorder...

The circuit is completely conventional, and is based on the application notes from National Semiconductor. The circuit is shown in Figure 1 and as you can see it uses a single IC and a few discrete components. The extra diode (D3) is included to ensure that the DC to the LEDs is almost unfiltered. C1 is included to make sure the IC does not oscillate, and is not a filter cap. This allows a higher LED current with lower dissipation than would be the case if the DC were fully smoothed, and full smoothing would also require a much larger capacitor...

The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs providing a logarithmic 3 dB/step analog display. LED current drive is regulated and programmable, eliminating the need for current limiting resistors. The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The input voltage can vary from 12V to 20V, but suggested voltage is 12V...

This ultra-bright white LED lamp works on 230V AC with minimal power consumption. It can be used to illuminate VU meters, SWR meters, etc. Ultra-bright LEDs available in the market cost Rs 8 to 15. These LEDs emit a 1000-6000mCd bright white light like welding arc and work on 3 volts, 10 mA. Their maximum voltage is 3.6 volts and the current is 25 mA. Anti-static precautions should be taken when handling the LEDs. The LEDs in water-clear plastic package emit spotlight, while diffused type LEDs have a wide-angle radiation pattern. This circuit (Fig. 1) employs capacitive reactance for limiting the current flow through the LEDs on application of mains voltage to the circuit...

This project is also an essential part of the expandable analyser to be published soon (or perhaps "eventually"), and one meter circuit is used for each frequency band. There are many other uses for a simple LED VU meter. They are ideal as power meters on amplifiers, can be used with mixers (including the high quality mixer described in the project pages), preamps and any other application where it is important to know the signal level. The circuit is completely conventional, and is based on the application notes from National Semiconductor. The circuit is shown in Figure 1 and as you can see it uses a single IC and a few discrete components. There are two rectifier circuits so that the DC to the LEDs is almost unfiltered...

If two of these circuits are made in the same enclosure for stereo, then there can be a single power supply to run both of them. There should be a resistor in series with the incoming 9V+ lead so as to minimize crosstalk, and reduce the PLOP when it`s powered on. Other features can be added to this basic mixer. One or more microphone preamps could be added. A VU level meter or LED bargraph can be added. The microphone preamps could have a transformer to match a low impedance microphone to the preamp input. Etc.....

This nifty sound level meter is a perfect one chip replacement for the standard analog meters. It is completely solid state and will never wear out. The whole circuit is based on the LM3915 audio level IC and uses only a few external components. This circuit can also be integrated into audio amp projects...

VU (Volume Unit) meters used to be the mainstay of audio metering systems, but they have been replaced by LED metering in a great many mixers and other applications. Even in software, the most common level meter is made to look like an LED meter. The Peak Programme Meter (PPM) was originally developed by the BBC to overcome the shortcomings of the VU meter, which is notoriously bad at showing the peak signal level. The VU meter is average reading, and the ballistics are important if an accurate reading is to be obtained...

Peak reading meters, popular in Europe for years, are just now coming into greater favor in America, and for good reason. The main purpose for having a VU meter is obviously to monitor signal levels going to a tape recorder, reverb unit, or some other level-sensitive device, to help optimize the signal to noise ratio of the audio sent to the device. Too much level will produce distortion, and too little results in the inherent noise of the medium becoming a problem. Unfortunately, a conventional VU meter responds to the average level of the program material and not to the peaks; yet it is these momentary bursts of higher level that become distorted first...

The circuit inFig 1 can detect the peak of either positive or negative inputs, yet it operates from a single supply. The circuit uses two unity-gain amplifiers to monitor the input signal, one an inverting amplifier and the other a noninverting amplifier. A typical application is driving a VU meter. The design takes advantage of a characteristic of the LMC662, IC1. Although the op amps data sheet warns against pulling inputs below ground, the op amp can withstand negative inputs if you limit the input current. In this circuit, R1 limits input current to a very small amount...