Charge pump capacitor values

[tubegeek]

> pull out your slide rule

No.  ...
You memorize several land-marks to get your place.

I remember ....

So you become a "human nomograph" over time, then? Got it. In much the same way, I've memorized that 1/2π = .159, which is not any more useful than the obvious rounded estimate of 1/6 unless for some reason we NEED 3 place precision, and that is rarely a requirement in an audio device. (RIAA phono networks are the only place I can claim to have "heard" the benefits of even 2-digit precision.)

For "mental math," 1/6 is much, much more useful, and of course is easy to remember when you are staring at 1/2π.

Math teachers call this stuff "number sense" and it is very hard to teach if everyone is constantly busting out their calculator to find the exact answer to 33 x 3.

[PRR]

> I've memorized that 1/2pi = 0.159

I do not think I have ever used 1/pi.

This may be in how I work fractions. Like an abstract painting, or a PCB, which side is "up" is just a matter of reference. You flip it upside down and back at your convenience, just making sure you end-up at the reference upside. Lacking memory (scratchpad or in calculator), I would work the bottom first, then 1/x, then work the top.



Pi is is not equal to 3 in Indiana, but "3" is usually good enough for me, all first-order and nearly all second-order audio problems.

[tubegeek]

> I've memorized that 1/2pi = 0.159

I do not think I have ever used 1/pi.

For me, doing capacitive reactance, I might do a 1/(R*C) calc first (because they are often roundish numbers) and then multiply the result by 1/6. What you're saying is you'd do 6 times R*C and then flip it. Same difference. I'll do the same thing if I have numbers I can multiply in my head by 6 easier than by 16. (the .159 step.)

This may be in how I work fractions. Like an abstract painting, or a PCB, which side is "up" is just a matter of reference. You flip it upside down and back at your convenience, just making sure you end-up at the reference upside.

When a student finally gets that division and multiplication are all the same damn thing, and what a reciprocal means in that context, that's when I find they can really start getting somewhere.

Pi is is not equal to 3 in Indiana, but "3" is usually good enough for me, all first-order and nearly all second-order audio problems.

Yes, that's only off by less than 5%. That's almost always below the threshold for audio accuracy.

I will say that, when I was tweaking phono preamps, there really were audible differences in the overall timbre as I was adjusting the parts down to a few percent accuracy. There were definitely bigger differences to be heard with small channel mismatches than with absolute EQ accuracy, but the absolute accuracy was also more important than I expected. That is the result of the compound shape of the curve and the placement of the corner frequencies right smack in the middle of the midrange I guess.

[Sage]

I think, from your reaction, you maybe have misunderstood what PRR meant.

What he's saying is: if you do an Ohm's law calculation, using the maximum specs of the chip (24V and .1A, I'm assuming) the worst-case scenario for your load (the single op-amp, which is all that you are powering with that power supply) is that your circuit must look like an impedance no lower than 240 ohms from the supply's point of view.

BUT: you are well within that limitation because your circuit is drawing far less current (1/20th of it) so it looks to the supply like an impedance 20 times larger, so let's say 4800 ohms. (You could round to 5K if you like that better to calculate with.)

Ah, yes, you're right, that's exactly what I wasn't getting.  Thanks for straightening that out for me.