Ok, after looking at several different hobby websites and whatnot, as well as raiding the local RadioShack once more, I came up with a TL082 (Yay!
). I want to make a two stage amp from this with volume trimmer. The only thing I could dig up that I could fit easily was a 100K
hm: stereo trimmer, R3. Since it's got two pots ganged together, I figured I could wire them both into both TL082 stages' negative feedback. I don't know if it is acceptable to control both stages' gain at the same time, or if I should only adjust a single stage. If I should only adjust a single stage, I'm guessing that it would be better to adjust the secondary stage. This way the primary stage would output a constant gain at low noise to ensure a strong clean signal for the secondary, correct?
I drew out and attached my design. Any obvious flaws? I was unsure of how to couple the two, so I borrowed this idea from a hobby site. I have a 1uF tantalum capacitor, C3, and a 10K
hm: resistor, R5. Also, in order to provide both positive and negative voltage, I used two 100K
hm: resistors, R1, to provide ground so that I have + and - 4.5 Volts from a single 9V battery. I'm unsure if this is sufficient voltage differential to perform my desired task. I'm guessing this sets the maximum peak to peak output possible at 9V?
Also, I found on one site the idea of sticking a 10K resistor, R7, across the output. The reason given was to provide a DC ground reference to the next circuit, since the output is decoupled. The example circuit did not have a zobel network. A zobel network doesn't look like it would provide a DC ground reference. Is it necessary to provide this ground reference? I have had previous troubles with AM reception when touching the mic, so I'm wondering if this would solve the ground problem. Also, if this is a good thing to have, should I throw in a zobel network in addition, or does this resistance provide sufficient load as well?
Lastly, the site I used as a guide to design this circuit used 10uF capacitors to decouple at both input and output, C2 and C4. In the previous designs discussed, the value for the output cap was larger. Using a reactance calculator, it seems as if either 10uF or 22uF would have much less than 1
hm: resistance at audio frequencies. This makes me think that either value would work equally well? I picked up a few tantalum 10uF capacitors I could use for C2 and C4. Would these be reasonable to use? I'm interested to know if electrolytics are better/worse, and if 10uF is acceptable.
TJ