While it could have been made faster by limiting the opamp output swing with more diodes, doing so would increase complexity and introduce switching noise onto the input line. The aim of the circuit is to detect both positive and negative peaks - a great many peak/ overload detectors only work with one polarity. This is not really a good idea, because many (most) audio signals are asymmetrical, and detecting only one polarity could mean that some signals could be clipping without you realising that it's happening.Īnother requirement is that the circuit can be connected to high or low impedance circuits without creating a non-linear load that causes distortion. This is especially true with high impedance circuits, because any non-linearity in the detector is directly reflected back to the source. An overload indicator that creates distortion in the source circuit is hardly useful.Īlthough shown here using ☑5V supplies, these circuits will all work fine with other supply voltages. The detection thresholds are set from the supply rails, and the ratios remain the same regardless of supply voltage. Only the LED series limiting resistor will need to be changed in order to maintain a useable current at reduced voltage. Amp clipping detector series#įor example, with ±5V supplies, you might reduce the LED series resistor to around 820Ω. The circuit diagram is shown in Figure 1, and although shown with an LM358 opamp, you can use TL072, 1458, 4558 or any other common (cheap) dual opamp. While you can also use expensive high-performance opamps, there is no reason to do so - the circuit only lights an LED. The biggest advantage of the LM358 is that the output can swing to the negative supply rail, so there is no chance of the LED being on all the time. For other opamps, it will be necessary to reduce the value of the 10k resistor from base to emitter on Q1. Where very high impedance is needed, the TL072 is suggested because its input bias current is very low, minimising errors caused by the input current. This is rarely necessary.ĭespite the simplicity, the circuit works very well. If used with a mic preamp or similar, VR1 (trimpot) will allow you to set the peak voltage where the LED will come on. With VR1 at maximum, the detection voltage is about 10.7V, so there is almost no headroom before the signal clips. Normally, I'd expect VR1 to be set to roughly 1/2 resistance, which provides a detection threshold of ☘.3V. This is about the maximum you'd normally use for a circuit operating with ☑5V supplies. Setting VR1 to lower resistance reduces the detection threshold voltage. At a 10% resistance setting (5k) the detection threshold is ☓V. If desired, a fixed resistor can be used instead of the trimpot. U1A and U1B form what's known as a 'window comparator'. Provided the signal voltage remains within the boundary reference voltages at pins 2 and 5, the outputs remain at close to -15V.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |