So this will illustrate how much of a novice I am. I successfully built a preamp using two opa2134 ICs on breadboards supplied with a nice 15+/- vdc linear supply. sounds great but the pot going between the two opamps doesn't turn down the volume. it's a 10K audio taper. I tried using a 1M in its place and all it does is add noise when it's turned down, no level attenuation. I'm clearly doing something wrong here. I have both opamps wired with closed loops for unity gain. again, sounds really fine, so I'm not unhappy here, just need to know what I'm doing wrong to not get any level control
yes I had wired it wrong, I realized after I thought about this for a little while that I need to build a simple voltage-divider network instead of just having the pot try to attenuate the signal by itself. in other words, I was trying to use just two (for one channel) terminals on the pot, when I should have been using three. so I did this and it's working as it should now but the attenuation is only in the first sixth or so turn of the pot so I am going to try to add a resistor to see if I can remedy that (I want to try to keep the 10k pot and not replace it with a different value because it's already implemented in my "box" somewhat permanently with a nice knob I had to glue on with epoxy glue because it wouldn't quite fit on the shaft LOLOLOLOL). any suggestion? add a resistor in series? (referring to one channel at a time here)
ok I did the arduous math and figured it out. had to put a resistor in parallel to R2 in the voltage-divider network (using another pot for now). It worked, getting attenuation through the whole knob now. I guess it's true what they say: "DO THE MATH"
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yes I am using a logarithmic 10k. contrary to my prior post (please excuse me because at the time I was ramped up on caffeine), adding the resistors in parallel in the manner I posted did not work all that well; what I ended up doing was putting another pot, a 25k logarithmic, in tandem, wired in the exact same way as the 10k, so both pots are in parallel to each other. then I played with the 25k until I found a position where the 10k actually provided a fairly smooth attenuation contour through the rotation of most of the knob. then I mounted the 25k pot inside of the box in order to leave it at the one setting permanently (yes I could have measured it with a multi-meter and replaced it with some resistors of the same value, but I do not have resistors just lying around and I am needing to finish this project today before getting back on the road again tomorrow).
so I am happy with this result, preamp sounds totally transparent. again, I had already permanently mounted the 10k pot with a nice knob glued onto the shaft as it wouldn't quite slide onto the shaft on its own, so I had to try to get the 10k pot to work well without replacing it with some other pot. I am pleased with the result.
so I am happy with this result, preamp sounds totally transparent. again, I had already permanently mounted the 10k pot with a nice knob glued onto the shaft as it wouldn't quite slide onto the shaft on its own, so I had to try to get the 10k pot to work well without replacing it with some other pot. I am pleased with the result.