Saturday, April 13, 2013
Clipping Indicator For Audio Amplifiers
A clipping indicator is a useful accent on any audio amplifier. It indicates when the amplifier has reached its restrict and is clipping the peaks of the audio sign. In observe, a great deal of clipping can happen prior to which you might hear it. So why is it necessary to underneathstand when an amplifier is clipping if that you couldt no longerice it? The solution is that clipping \"squares up\" the waveform and sq. waves incorporate lots of higher-frequency harmonics which will easily harm the tweeters in loudspeaker techniques. This circuit is a real clipping indicator as adversarial to the extent warning signs which might be recurrently utilized in preamplifier levels.
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The problem with stage indications is that an amplifiers maximum output power is not regular. Thats since the amplifiers provide rails aren't regulated and so the utmost power available at any given fast varies, depending on the applied sign. The circuit is rather simple and is in accordance with two BD140 PNP transistors and zener diode ZD1. During customary operation, Q1 is fliped on by way of ZD1 and R1. As a consequence, Q2 is held off (since its base is pulled high) and so LED1 can additionally be off. However, if the output sign therefore upward pushs to within 4.7V of the sure supply rail, Q1 turns off because it no longer has any ahead bias on its base.
Circuit diagram:
Clipping Indicator Circuit Diagram
As a end result Q2s base is now pulled low by way of R2 and so Q2 turns on and light-weights LED1. (Note: the 0.6V drop across Q1s base/emitter is omitted right here as a end result of ZD1 conducts ahead of its rated voltage as a consequence of the very low current involved). Why select four.7V beneath the energy rail as the turn-on point? The reason is that, because of the drive limitations and the nature of emitter followers, they can be anticipated to have as a minimum 4V across them when they saturate (ie, clip). ZD1 can additionally be elevated to a 5V or 6.2V type if the circuit is for use with a monster amplifier.
The worth of R3 should be customized in retaining with the amplifiers supply rail, so that LED1 operates with the precise brightness. To do this, first measure the amplifiers positive provide voltage, then use Ohms Law (R = V/I) to calculate the worth of R3 for a current of about 20mA. As it stands, this circuit can most effective be used to watch the certain-going half-cycles of the audio waveform. If you need to observe the poor half-cycles as smartly, you could have to build a 2d circuit with the next changes: (1) reverse both LED1 and ZD1; and (2) use BD139 (NPN) transistors for Q1 & Q2. Note that, in each instances, you wish to use the earth within the amplifier, because the speaker poor will not be earth (such as in a bridged output).
Author: Philip Chugg - Copyright: Silicon Chip Electronics Magazine
