Hi fubar3,
Where did the FIGURE 10 in first post come from? Part (b) is a complete mess and some of the subsequent posts are incorrect.
If the feedback Ref Des is revised to be R2 as suggested by ejp, and at large frequencies where the caps can be treated as shorts,
gain = Out/In = +(R1+R2)/R1 and is commonly rewritten as: 1+R2/R1.
At DC, the gain is 1 as explained earlier. The low frequency breakpoint where the response fails about 3dB from the AC gain occurrs when the reactance of C2 equals R1. Fc = 1/(2*Pi*R1*C2)
In the example case where R2=10K, R1=1k, and the desired corner frequency is 3Hz, C2= 1/(2*Pi*3Hz*1k) = ~ 53.1uF.
Where did the FIGURE 10 in first post come from? Part (b) is a complete mess and some of the subsequent posts are incorrect.
If the feedback Ref Des is revised to be R2 as suggested by ejp, and at large frequencies where the caps can be treated as shorts,
gain = Out/In = +(R1+R2)/R1 and is commonly rewritten as: 1+R2/R1.
At DC, the gain is 1 as explained earlier. The low frequency breakpoint where the response fails about 3dB from the AC gain occurrs when the reactance of C2 equals R1. Fc = 1/(2*Pi*R1*C2)
In the example case where R2=10K, R1=1k, and the desired corner frequency is 3Hz, C2= 1/(2*Pi*3Hz*1k) = ~ 53.1uF.
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@BSST asks: Where did the FIGURE 10 in first post come from? Part (b) is a complete mess and some of the subsequent posts are incorrect.
I saw it in an opamp cookbook, I provided the link. I did not notice that the non-inverting snip had two R3 resistors to confuse discussion. I wanted to know the purpose of the shunt cap, whatever it is called and Boden asked how C2 is calculated. I did not understand the responses but I found a couple of Rod Elliot projects that have the feature in question. They happen to be white-pink noise generator. It seems the purpose of the shunt cap in the feedback network is to reduce infrasonics or out-of-band subsonics which can stress your woofers.
I saw it in an opamp cookbook, I provided the link. I did not notice that the non-inverting snip had two R3 resistors to confuse discussion. I wanted to know the purpose of the shunt cap, whatever it is called and Boden asked how C2 is calculated. I did not understand the responses but I found a couple of Rod Elliot projects that have the feature in question. They happen to be white-pink noise generator. It seems the purpose of the shunt cap in the feedback network is to reduce infrasonics or out-of-band subsonics which can stress your woofers.
If you're referring to C2, it would be referred to as a "series" cap, and the description you've related is correct. It's in this circuit, it attenuates low frequencies and helps minimize DC present at the output. In a power amp, it minimizes DC applied to the speaker voice coil.
Some applications might connect a cap in parallel with R2. The cap would be said to "shunt" R2.
Some applications might connect a cap in parallel with R2. The cap would be said to "shunt" R2.