So here's the deal. I have an LM386-based chip amp, and I'm trying to put a volume pot before the input. When I wire it as shown in the top image, the pot works (e.g., it controls the volume), but the "maximum" output (e.g., pot turned to "10" or "zero resistance"), I only get about 1/5 the expected volume output. Now, my hunch is that my pot value (1k) is too low, so even when "dimed," the pot is basically bleeding off a lot of the signal to ground.
My question is this - in the second schematic (e.g., not grounding the third tap of the potentiometer, essentially using it as a rheostat), the pot doesn't control the volume at all (at least, I can't hear any difference). Why is that? Wouldn't dropping a 1k ohm resistor (e.g., when the pot is set to "zero" volume or "full resistance") in the signal path have some effect on volume? Or are the pickup and amplifier impedances just too high to have 1k make a discernible difference?
I will test out a 500k pot when I get a chance, but I'd like to know the theory behind what's happening here.
Thanks in advance.
My question is this - in the second schematic (e.g., not grounding the third tap of the potentiometer, essentially using it as a rheostat), the pot doesn't control the volume at all (at least, I can't hear any difference). Why is that? Wouldn't dropping a 1k ohm resistor (e.g., when the pot is set to "zero" volume or "full resistance") in the signal path have some effect on volume? Or are the pickup and amplifier impedances just too high to have 1k make a discernible difference?
I will test out a 500k pot when I get a chance, but I'd like to know the theory behind what's happening here.
Thanks in advance.
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Thanks! And do you think the too-low-value also causing the phenomenon in circuit #2? (E.g., 1k just isn't enough to make a difference in a rheostat-style configuration?)
Essentially, I'm effectively presenting a 51k input to the guitar instead of a 50k input, which just isn't enough to make a dent?
You make a voltage divider consisting of the amplifier input impedance, which is apparently 50 kohm, and the 1 kohm rheostat. That results in a gain of 50/51 times the maximum, or -0.172 dB with respect to maximum gain. That's almost no gain reduction. In fact that -0.172 dB is a too optimistic estimate, because the source impedance is also in the equation and makes it even closer to 0 dB.
You wrote something about a guitar. An electric guitar pick-up has a quite high impedance and requires a load impedance of the order of 200 kohm...1 Mohm including the effect of the volume control potmeter inside the guitar.
You wrote something about a guitar. An electric guitar pick-up has a quite high impedance and requires a load impedance of the order of 200 kohm...1 Mohm including the effect of the volume control potmeter inside the guitar.