This will not bother most solidstate preamps but will add distortion on a few tube preamps. Calibrated Level Eliminates Audible Noise) is a simple LED indicator system now available on new Punch amplifiers designed to help eliminate speaker. The input impedance changes from near infinity below 0.4V to a few dozen Kohm above that. If you light this LED with these amps they are already in gross clipping. There are "some" power amps with much lower sensitivity numbers, like 0.6V. This light will tell you to turn it down. On musical climaxes, if either side clips, both sides are near clipping. I have also worked with Male Speech which can have consistent asymmetry but we rarely want to hear this LOUD and anyway a bit of clipping does not hurt speech intelligibility. Indeed, it is new to me as well, since this is a method of detection I have never seen published in any (even remotely similar) form. Although a simple circuit, it uses a principle of operation that will be new to many readers. While I have seen many single-sided transients they were only a half cycle and thus "brief", hardly worth knowing. Figure 1 shows the circuit of the detector. It won't be an exact fit, but short clipping is fairly benign and extended clipping is bad- this gives you a clue. A light detector circuit is a circuit that can detect light. Theory: In this project, we will build a light detector circuit using a NAND gate chip.
More to the point: it may turn-on with 1.2V steady, but brief musical transients may have to exceed 1.7V to discharge C1 enough to allow Q2 to turn-off.įor power amps with typical 1.0 to 1.2 Vrms rated sensitivities, this will approximately indicate "clipping". Objective: Light detector using NAND gate. Rule-o-thumb says 2.5*Vbe but Vbe will vary with device (and temperature). Or, maybe you just drive the audio circuit into hard-obvious clipping and adjust R5 until the LED 'just comes on', and cross your fingers and hope that 'slight clipping' is also detected. So, you need an oscilloscope to calibrate to the clipping point.
The input needed is almost independent of supply voltage and is between 1.2V and 1.8V. R5 should be adjusted to so LED comes on at (or near) the clipping point. Q2 sits normally hard-ON, shorting-out the LED so it stays dark.Īn input which turns Q1 on will turn Q2 off, lighting the LED.