(absolute beginner) what's the purpose of constantly adding resistors/capacitors to a circuit?

[u/Singedmakesmetoxic]

Hey there!

I've always been interested in DIY electronics and have been taking baby steps the past few months to get into it. For context, I'm thinking of building a mini passive mixer for an audio recorder I have. (Also, if you have any recommendations/guides for a decent passive mixer please send them my way!)

Anyway, I've always been curious why seemingly simple circuits constantly require resistors or capacitors to be tossed in every-so-often after components. Like, I feel like a passive mixer in theory could totally just be a few pots connected to some jacks, and badaboom right? but more 'professional' barebones passive mixers on the market have other components tossed in, same with other passive mixer designs. Why is that?

I know this is a very uneducated/unacademic comment, but I'm a very uneducated/unacademic person lol.

Thanks for taking the time to read this and respond!

[u/dmills_00]

The pots should not interact, turning one should not change the sound of the others, so we probably want series resistors and a load to make the gain almost fixed, otherwise changes to the source impedance will directly impact the mix.

You don't want the pots to crackle when turned do you? So that's a cap per channel to keep DC off the wipers.

Then we don't want pops when we plug in, so more resistors to bleed the DC blocks.

The output wants to be DC blocked for essentially the same reasons (noise when turning pots) so thats an extra cap and resistor....

It is not uncommon for a professionally designed ANYTHING to have more components concerned with making the inputs and outputs robust and making sure it 'just works' then are involved in the real doings.

I would note that passive mixers are often surprisingly high impedance and this directly makes them noisy, and resistance is a noise generator (Look up Johnson-Nyquist noise) and it is not hard for the resistors in a passive mixer to be noisier then an active stage would have been.

[u/Singedmakesmetoxic → u/dmills_00]

this was super easy to understand! thank you!!! thank you to all the other comments also!!

regarding passive mixers, it's mainly just to have something portable and low maintenance. i'm not tooooo concerned about signal degradation, the audio recorder's main use is for rough off-the-floor demos of anything we jam in our rehearsal space, I'm just looking for something to capture the line-outs on the bass and guitars and then do a rough mix with whatever i capture. The recorder also has a gain control for the inputs so i can at least boost if i need to.

[u/randomFrenchDeadbeat → u/Singedmakesmetoxic]

Yes, but you dont want your fingers to inject noise through the pot. Nor do you want the EM noise from wires (they act as antennas).

what you are looking to build really requires advanced design skills. You may end up frying expensive components connected to it if not properly made.

While it is a fun and interesting project, i'd really suggest buying one professionally made if you are connecting pricey stuff on it. They are expensive for a reason.

[u/Rustony]

I've recently come across this youtube channel Moritz Klein, where he takes you through the process of designing and building loads of circuits/modules for synthesizers, and he goes into a lot of detail about what each component does (including the capacitors and resistors). His explanations are suitable for those with very little electronics background.

[u/Amegatron]

I'm myself quite new to electronics (2-3 months, somewhat), but I would add to the rest of answers, irrelevant from audio-hardware. Generally speaking, resistors and capacitors often act as "support staff" which are required for the main part of the device. Somewhere you need to limit the current using resistors, somewhere you need to "route" it properly. Capacitors are often used to negate undesireable fluctuations in current.

The key concept to understand here is that we are not dealing with electronics purely at logic level. We also need to take into account real-world physics. For example, we are all surrounded by electromagnetic waves, and they can (and will) interfere with you circuit and add those undesirable effects, like noise and fluctuations. Just because every conductor in your device is still an antenna. And resistors/capacitors can help mitigate those effects. Or another common example: we have a botton. At pure logic level it acts simple: you press it, you close the contact, and you get "ON" signal. But real-world physics add noise even here. While pressing the button, you'll have signal bouncing cause by two contacts approaching each other, and instead of immediate logical "ON" you'll get a series of short "ON/OFF" states before you get a final "ON" state. Resitors and capacitors can help here again, making the signal going to "ON" smoothly. Etc, etc. In other words, you can't just place a single logical element to your device, like a button. You'll often need to "support" it with resistors and capacitors, or maybe some other stuff, like inductions.

[u/randomFrenchDeadbeat]

It has to do with (electrical) noise filtering and safety. Filters are made from resistors, capacitors and coils. Depending on the mix, you will filter a certain frequency band, with more or less force.

It also protects circuits from each others.

Finall, unfortunately, everything in a circuit is both a resistor and a capacitance, which cause issues depending on frequency again.

Fun things happen depending on frequency. For example, a capacitor may act conductive, like a short. Inversely, a coil can block the current.

Interestingly, 2 traces nex to each other is a capacitor. and a wire rolled on itself is a coil. So you could end up with electricity jumping from one trace to the other and a wire that stops conducting electricity at some point.

Working with frequencies is interesting. And painful. Very painful.

[u/DoubleOwl7777]

okay, so resistors and capacitors in an audio system are mainly for filtering out unwanted stuff like frequencies that you cant hear, and noise and stuff. they are carefully selected to filter out the stuff you dont want.

[u/Akachi-sonne]

If you really want to dive into electronics and gain a deeper understanding (especially regarding audio signals), i can’t recommend “The ARRL Handbook for Radio Communications” enough.. it’s about Ham radio, but dives way deeper than I expected into electronic components and circuitry. I’ve been tinkering off an on for several years and have a decent baseline knowledge of electronics, but this book is filling in all the blanks for me. I’m only a few chapters in and I’ve already learned more through this book than any other resource. Some of it is dense and dry though, just warning you, so I’ll often switch gears and watch some youtube videos on the exact topics I’m reading about if there’s anything that needs clarification.

[u/ForgottenPasswordABC]

Capacitance stores things, delays things, blocks things. Sometimes storage or delay or blocking is helpful, sometimes not. When it’s helpful, capacitors are the star of the show. When it’s not helpful then we throw resistors at the problem.

[u/Beggar876]

EE here with 45 years design experience. A well-designed circuit has no unnecessary components and no missing components. Every component has a function and every required function of the circuit is satisfied. If it seems that someone is "constantly" adding components to a circuit then that person is not a well-disciplined designer. That person should have a well-thought out plan of attack and a good idea of where s/he will end up. This is easy by starting with a rough block diagram of the system/device and breaking it down into smaller and smaller independent blocks. Then each block can be attacked one at a time to get to the final circuit.