Not using the entire potentiometer in a buffered volume pedal circuit?

[midwayfair]

Still need the huge cap to go to ground here, paralleling the resistor that goes to ground?

Not in parallel with the resistor -- in series with it. Take a look at the first stage of the greenbean for an example of a variable gain amplifier. The resistor and capacitor coming off the inverting pin to ground controls the negative feedback. You won't necessarily want to use the values in that circuit here because they cut a lot of bass, but it will give you an example.

AMZ has a multi-purpose buffer/booster here: http://www.muzique.com/tech/opamp_multi.htm
That one uses an inverting amplifier for the second stage, which is fine as long as you have the first buffer so your pickups don't change the gain.

Here's a good handout on explaining a lot of stuff about an operational amplifier. Not much math (thank goodness), and it goes into good detail: http://web.stanford.edu/class/ee122/Handouts/2-Op-Amp_Concepts.pdf

[brand0nized]

Okay, so a voltage divider network can create gain where gain(A) = 1 + (R2/R1) where R2 is between the pin 2 (inverting input) and pin 1 (output) and R1 goes from pin 2 to ground (or to a cap which goes to ground)?

What does the cap do?

[midwayfair]

What does the cap do?

Decouples it, and it will also set the -3dB high-pass ("bass cut") cutoff frequency of the gain together with the resistor that's in series with it, and then the gain will boost with that as the bass cutoff frequency. The formula for the -3dB cutoff of a filter of any sort is always 1/Tau*R*C. But just use a calculator: http://sim.okawa-denshi.jp/en/CRhikeisan.htm

Put another way, the non-inverting amplifier will be an active high-pass filter. If you want to tailor the bass a little bit when you inch up the gain, you can do it that way, or you can just use a big capacitor, like 47uF or 100uF, and you'll boost everything.

Okay. I haven't gotten into another slightly simpler way: You can leave out the capacitor and just use a resistor to Vb instead of ground. You won't be able to get as much gain as the method going to ground, but if you're only trying to get a smidge more gain, that will save you the extra part and the headache of figuring out the frequency.

[brand0nized]

What does the cap do?

Decouples it, and it will also set the -3dB high-pass ("bass cut") cutoff frequency of the gain together with the resistor that's in series with it, and then the gain will boost with that as the bass cutoff frequency. The formula for the -3dB cutoff of a filter of any sort is always 1/Tau*R*C. But just use a calculator: http://sim.okawa-denshi.jp/en/CRhikeisan.htm

Put another way, the non-inverting amplifier will be an active high-pass filter. If you want to tailor the bass a little bit when you inch up the gain, you can do it that way, or you can just use a big capacitor, like 47uF or 100uF, and you'll boost everything.

Okay. I haven't gotten into another slightly simpler way: You can leave out the capacitor and just use a resistor to Vb instead of ground. You won't be able to get as much gain as the method going to ground, but if you're only trying to get a smidge more gain, that will save you the extra part and the headache of figuring out the frequency.

Yup, just enough gain to make up for the pot not being turned all the way.

With A = 1 + (R1/R2), I want to do R1: 10k and R2: 5kb trimmer, so that max gain will be limited and I can accurately dial in the gain to be unity at toe down position. Does that work? Also, where would the third pin of the trimmer go? Ground?

[midwayfair]

What does the cap do?

Decouples it, and it will also set the -3dB high-pass ("bass cut") cutoff frequency of the gain together with the resistor that's in series with it, and then the gain will boost with that as the bass cutoff frequency. The formula for the -3dB cutoff of a filter of any sort is always 1/Tau*R*C. But just use a calculator: http://sim.okawa-denshi.jp/en/CRhikeisan.htm

Put another way, the non-inverting amplifier will be an active high-pass filter. If you want to tailor the bass a little bit when you inch up the gain, you can do it that way, or you can just use a big capacitor, like 47uF or 100uF, and you'll boost everything.

Okay. I haven't gotten into another slightly simpler way: You can leave out the capacitor and just use a resistor to Vb instead of ground. You won't be able to get as much gain as the method going to ground, but if you're only trying to get a smidge more gain, that will save you the extra part and the headache of figuring out the frequency.

Yup, just enough gain to make up for the pot not being turned all the way.

With A = 1 + (R1/R2), I want to do R1: 10k and R2: 5kb trimmer, so that max gain will be limited and I can accurately dial in the gain to be unity at toe down position. Does that work? Also, where would the third pin of the trimmer go? Ground?

Looks right in the description at least.

The third leg of the trimmer isn't needed; it's just a variable resistor.

[brand0nized]

Looks right in the description at least.

The third leg of the trimmer isn't needed; it's just a variable resistor.

Excellent! I'll redraw the schematic when I get home.

[brand0nized]

Alright, here it is. Variable gain should be the last thing I need in this circuit.

Does all seem right?

[m-Kresol]

You need to hook up pin 2 of your trimmer to another leg of the trimmer (preferably 3, so the resistance increases as you turn the pot and therefore have more boost). The way you have it, the trimmer wont do anything when you turn it


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[brand0nized]

You need to hook up pin 2 of your trimmer to another leg of the trimmer (preferably 3, so the resistance decreases as you turn the pot and therefore have more boost). The way you have it, the trimmer wont do anything when you turn it


Sent from my iPhone using Tapatalk

Oops, you're totally right.

But other than that, all is well?