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A conventional transistor amplifier has three stages, a differential input
stage, a voltage gain stage and an output stage current buffer. Each stage adds
its own contribution to the sound of an amplifier.
I have found that to an extent minimising the amount of main loop feedback is
a good thing. This in turn requires that each stage should behave
better by it self, if overall performance is not to suffer. As the main loop
feed back is reduced, the sound of the amp starts to open up and the character
of the individual elements starts to become apparent.
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I have not compared the effect a differential long tailed pair has on the sound relative to the
single ended, with emitter feedback, input circuits used in older amplifiers. Studying the voltage feedback vs
current feedback opamps however, it can be seen that the voltage feedback devices are not as fast... which
ultimately won't help.
I found a subjective difference in the voltage gain stage with the first
attempt conventional amp and the "improved" conventional amp. This demonstrates the
single ended / push pull effect the voltage gain stage can have on the sound. |
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output stage also contributes to the sound. To make a higher power amplifier, the
"improved" conventional amp had a steroid loaded output stage added to it,
whilst maintaining the same input and gain circuits. I was not expecting any
difference in the sound quality of these two amplifiers, just more power. I was
quite shocked therefore when I powered up the first prototype. The "improved"
conventional amp sounds light and ethereal, the high power version sounds
brutally and effortlessly powerful, even with the little Tandy speakers, it was
almost as if iron fists had seized the cones of the speakers!!! |
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Last changed: Sun Feb 26 20:09:23 GMT 2006
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