I haven't been able to find a good explanation of why capacitors act only on certain frequencies.
I'll read something like "change C3 to 22nf and you'll get more bass". Does it work the same for caps on the audio path and to ground (I feel like I've seen similar guidance for both)? Is it the same in all circuits? Do y'all just have the capacitance to frequency memorized or are you applying a formula?
I haven't been able to find a good explanation of why capacitors act only on certain frequencies.
I'll read something like "change C3 to 22nf and you'll get more bass". Does it work the same for caps on the audio path and to ground (I feel like I've seen similar guidance for both)? Is it the same in all circuits? Do y'all just have the capacitance to frequency memorized or are you applying a formula?
Caps have a "rise time" or charge time, depending on their value. When the wavelength time of a particular frequency is shorter than the rise time, that AC looks like DC to that capacitor. Caps block DC.
Edit to add, this is part of reactance. In the pedal world we don't really talk about reactance enough. And I'm not going to here. Google it muh guy/gal.
I haven't been able to find a good explanation of why capacitors act only on certain frequencies.
I'll read something like "change C3 to 22nf and you'll get more bass". Does it work the same for caps on the audio path and to ground (I feel like I've seen similar guidance for both)? Is it the same in all circuits? Do y'all just have the capacitance to frequency memorized or are you applying a formula?
This might be more info than what you were looking for, but if you read the following 3 articles, you'll have a good understanding. And you'll find the formulas.
Caps have a "rise time" or charge time, depending on their value. When the wavelength time of a particular frequency is shorter than the rise time, that AC looks like DC to that capacitor. Caps block DC.
the first one is voltage rating ... can't use 16v coupling caps in your tube amp. the other consideration would be the frequencies you allow through. since this sort of discussion usually revolves around signal amplification of some sort, the tendency is to filter off some bass to prevent blocking distortion and improve frequency response
I actually took a poop so I thought about it before typing...
To my knowledge:(*plunk*)
If it's a purely blocking cap *and there's only DC potential on one side of it*, then the capacitance rating electrically doesn't matter.
Now, if there's audio passing, you have to account for that and the ,essentially, blocking of low frequencies.
Also. Any series resistance to ground(forming a filter)--I know you know this but for completeness for future reader of my poop rambling...
Capacitive reactance comes into play. You can do the math, sim the circuit, or use ears/audio probe+spectrum analyzer.
I haven't been able to find a good explanation of why capacitors act only on certain frequencies.
I'll read something like "change C3 to 22nf and you'll get more bass". Does it work the same for caps on the audio path and to ground (I feel like I've seen similar guidance for both)? Is it the same in all circuits? Do y'all just have the capacitance to frequency memorized or are you applying a formula?
Calculate freuqency cutoff for guitar effects pedals with vacuum tubes and solid state electronics. FREE calculator.
www.muzique.com
So you can see from the two links above, it depends on how you're using the capacitor in circuit, what components surround it act upon or in concert with it.
The Muff's tone circuit is a great example:
Play around with JUST its cap values here to see what it does — with the tone knob centred, see how deep you can make the scoop, how flat, how mid-bumped:
If you have both the HPF and LPF with resistors 33k and capacitors of 10n, the corner frequency is the same for both the HPF and LPF, but because one is R>C>GND and the other is C>R>GND they have completely different outcomes. You'll have a flat frequency response with the Tone control centred at noon, BTW. So...
No, it doesn't "work the same for caps on the audio path and to ground", it depends.
Another great example from the Muff is the clipping caps — bigger caps would mean more bass, right? So wouldn't it be great to have really big clipping-caps for a bass Muff?
Turns out, in most cases, the answer is no.
Reducing the clipping-caps in a Muff limits the distortion to the higher frequencies and lows don't get clipped, and so seemingly lets more CLEAN bass squeak through the feedback-filter caps — more clean lows gives the impression of better bass response while the clipped mids and highs give us the distorted harmonics we seek in a fuzz sound.
Check out Kit Rae's Muff pages...
Scrolling through the Muff schematics on Kit Rae's site you'll see super-huge 1µF caps in the audio path of some of them, so you'd think they'd sound great on bass, but the clipping caps are just as big, so relative to each other the 1µF circuit is no more bassy than some Muffs with 0.100µF caps (100n) because of how the circuit is weighted/balanced. If you're 6'4" standing up straight in a pool of water that's 4' deep, the depth of the water is manageable; however, being the same height but you lie down in a pool of water that's half as deep at 2' ... so you see it's all relative.
Further to "it's all in how they're used..." take into consideration the Q or width of frequency bands in EQs. Here's a ProTools graphic to help:
Below is a couple of RCC combo examples, both elicit the same 400Hz corner-frequency, but the cap values are quite different:
Resistor
Cap 1
Cap 2
Hertz
Q-FACTOR
EX 1
120k
86n
33n
400Hz
Q=10
EX 2
68k
220n
22n
400Hz
Q=4
I know none of this explains the "WHY?", but I think that was already answered by others far more knowledgeable than I. Hopefully I didn't just regurgitate a bunch of things you already knew and that this post in some way helped you or will help others.
I'm still trying to wrap my brain around all this.
@jwin615, @spi - Thanks for the outline and links.
@Feral Feline - Wow, your repsonse is amazing, and very helpful! The Big Muff tone circuit is a great distillation of what I was looking for. I think I'll need to read your response a few times...
Hey, glad I could help in some small way. I'm impressed you've already laid out your own PCBs.
I'm still working up the courage to layout a single PCB.
Its pretty easy, especially for smaller circuits. It feels somewhere between a mildly pleasant chore (copying schematic) and a game (layout). I think between watching videos to learn KiCad and then trying a basic circuit it took me about 4 hours of time.
Really helps that ordering 3 different pcbs, each with 5 copies, costs <$15 shipped. I've already got my second order in .
They're not the same. The one on the right does not work as a filter. Well, maybe it does, depending what follows it, but on its own it's not an RC filter. The idea behind the correct filter (on left) is that the C and R form a frequency-dependent resistive divider, when you think of the C as a frequency-dependent resistor. This is the thing called capacitive reactance, which gets lower the higher the frequency.
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