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Post by pandapops on Mar 1, 2012 15:50:40 GMT
In a normal amp the signal goes through the volume pot and is moslty turned into heat, why not let the signal through barely changed and control the gain of the amp instead?
Obviously a mute button, or samll pot, and an amp that is stable over vaious levels of gain would be required. Is this so difficult for a headphone amp? Some pro mixing boards use variable gain so its probably affordable for a kit if not a finished consumer product. Why buy an audio grade pot or stepped attenuator when a trim pot could do the job by a different route?
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Post by Deleted on Mar 1, 2012 16:56:12 GMT
In a normal amp the signal goes through the volume pot and is moslty turned into heat, why not let the signal through barely changed and control the gain of the amp instead? Obviously a mute button, or samll pot, and an amp that is stable over vaious levels of gain would be required. Is this so difficult for a headphone amp? Some pro mixing boards use variable gain so its probably affordable for a kit if not a finished consumer product. Why buy an audio grade pot or stepped attenuator when a trim pot could do the job by a different route? In a volume pot (or attenuator) the audio input signal is simply divided depending on the position of the volpot, it is not dissipated away. Controlling the gain of an amplifier is actually feasible, it 'simply' consists of mounting a (linear) pot in the feedback path. This however, can cause instability problems and the bandwidth will also be dependent on the volpot position. There are more issues for not doing volume control this way. The gain control in mixing consoles is there to achieve: a: maximum S/N ratio - dynamic range over a wide variety of input levels (ranging from mV for microphones to volts for synths and other stuff). b: to give the volume sliders (attenuators) the optimal 'adjustment' range. Expensive pots and attenuators have a valid reason for their existence (within reason). a volpot (or slider in console) needs to be absolutely 'scratch free' as it is adjusted often. This requires more exact manufacturing (thus higher price). A volpot adjusts 2 channels at the same time and there must be good 'tracking' between the 2 'resistance tracks'. Meaning in every position the attenuation for L and R should be the same or within certain limits (stepped attenuators excel in this area). This is MUCH harder to manufacture in logarithmic pots and volume controls are log type.
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Post by Deleted on Mar 1, 2012 20:30:36 GMT
Also, PCB layout makes this difficult, with the need to extend the wiring of sensitive areas of the amplifier for user convenience. Frans's C.H.Amp gives the best of both worlds in this respect. Alexto
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