How to adjust the volume that serves as sound control fader with too linear potentiometer?
[introduction] did you ever serve as sound control fader with too linear potentiometer? If you had been used, you may discover, volume jumps become very fast. If want to adjust volume quite smally, you may need the acute touch like Safe-cracker. Need logarithm potentiometer at this moment.
Did you ever serve as sound control fader with too linear potentiometer? If you had been used, you may discover, volume jumps become very fast. If want to adjust volume quite smally, you may need the acute touch like Safe-cracker (the password that Safe-cracker can rely on his acute hearing to defeat interpret safe, author here is a kind of analogy, to linear potentiometer, the ordinary person is very difficult move volume quite smally) . Need logarithm potentiometer at this moment.
Our hearing has quite big dynamic range. Our ear (especially youth) the effective limits that can identify is 120dB bigger perhaps, 1000000: The rate of 1. Volume size (it is an unit with decibel) start depends on our aural ability, it is 1dB normally, this is the least volume change that we can feel. It is an unit with decibel, logarithm potentiometer is approximate linear, so, the change on buy of logarithm potentiometer v/arc be on the throne can bring the corresponding change on volume.
Graph the 1 logarithm potentiometer that showed the ideal on use linear potentiometer and maths will distribute the attenuation scale when pressing. Rotational potentiometer arrives the position of 50% , outputting voltage is input voltage 0.1 times (- 20dB) , in frequency potentiometer, this is a commonly used target cost. Potentiometer every are rotational 10% , output voltage can change 4dB. But ideal logarithm potentiometer has 40dB only merely when turning (input signal 1% ) damply (see a picture 1 medium enlarge part) . Audience hopes their sound control fader can achieve 0 output (the attenuation) of infinity, so logarithm potentiometer has an attenuation to eliminate a function (when logarithm potentiometer is not turning, output is to cannot be of 0, when turning to make logarithm potentiometer is in, be damply 0, must have this attenuation function) make when potentiometer is not turning, can achieve 0 output.
Have a lot of semiconductor standard curves about logarithm parameter (the firm says for degradation curve) . They appointed potentiometer normally turning the 50% attenuation factor when. Of standard of this kind of parameter naming is not very normative, so I won’t try to name them, this meeting brings more worries to everybody. If you have certain and special specific parameter requirement, seek advice from a manufacturer please. In certain applying, the likelihood needs special retrorse potentiometer. This kind of potentiometer is worth in the attenuation of different position and common potentiometer is contrary.
The degradation curve that the curve that logarithm potentiometer needs two section normally will come to reach expectation (if pursue 2) . Two kinds of different printing ink conductor are enchased to be in resistor (normally the circumstance falls, resistor is by dielectric and printing ink conductor is formed, different printing ink conductor, can cause different resistor block value, the curve that can bring these two section thereby) . Stereo volume pilot a crucial parameter is these two curves track precision. Ask an attention, in not rotational potentiometer when, output is 0.
You can use a linear potentiometer and a fixed resistor to come drive output, this is approximate at logarithm potentiometer (if pursue,3 are shown) . Use as when volume is controlled, this circuit still has a drawback of linear potentiometer——When potentiometer turns after all, volume jumps become too fast. The performance of this circuit is better than linear potentiometer, but for opposite logarithm potentiometer poorer. In logarithm potentiometer, this kind of resistor outputs circuit to be able to use the degradation curve that changes logarithm potentiometer likewise. Those who need an attention is to input signal to must want can output of drive resistor R1 is full a signal, and R1 can be a lesser resistor, this depends on the size of Rp.
In the user application of a few high volumes, electronic sound control fader had replaced traditional logarithm potentiometer substantially. The principle of electronic sound control fader is to use digital amount to control the logarithm of natural volume to increase, and used attenuation eliminate a technique (namely Walk-off) , make the bottom in degradation curve, attenuation value is 0. A lot of contemporary frequency parts of an apparatus offerred knob of rotate of a tine, rotational this knob, can generate the pulse signal of different frequency, will control the attenuation cost of electronic potentiometer. Besides frequency application, these parts of an apparatus also can apply in signal access. A few relevant parts of an apparatus are below:
● Gain of number of the buy before PGA2500 microphone can accuse amplifier
● Sound control fader of PGA2320 stereo frequency
● The only channel number that LM1971 has quiet tone function controls 62dB frequency attenuator
● LM1972 has the attenuator of frequency of 78 DB of Micro-Pot 2 passageway of quiet tone function
● LM1973 has the attenuator of frequency of 76 DB of Micro-Pot 3 passageway of quiet tone function
● TPA6130A2 has 138mW DirectPath of I2C volume pilot™Stereo earphone amplifier
● TPA6140A2 has 25mW G of I2C volume pilot kind DirectPath™Stereo earphone amplifier
● TPA2054D4A has stereo D kind amplifier and DirectPath™The 1.4W/ passageway of earphone amplifier subsystem of 3 inputs frequency
● TLV320AIC3262 has miniature DSP, compositive D kind the stereo of low power comsumption of driver of loudhailer, earphone and DirectPath makes up decoder
But, still a lot of circumstances use traditional sound control fader and logarithm potentiometer, so, an imitate stylist should be clear about these the basiccest circuit knowledge.
(origin: EDN electron technology is designed, author: Engineer of Bruce Trump senior imitate)
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