Guitar Pedal Power Filtering & Decoupling Capacitors

An explanation as to how decoupling capacitors and power filtering capacitors work in guitar pedals and audio circuits

[@josephrogers9796]

I like the way of your tutorials because they are in lay mans terms. I am new to guitar pedals and I need all the help I can get.

[@cassvirgillo3395]

Hi Paul, As you may know AC and DC can reside in the same line, wire, without mixing or changing each other. As you stated, the purpose of the capacitor is to block the DC and let the AC signal from the guitar, etc. through. The same holds true in guitar tube/ valve amps from the plate of the tube/valve. A higher value cap will eliminate more ripple, or, better yet, a series of caps separated by resistors. Your information jives with what I have learned in regards to electronics. You are a credible channel, worth a subscription. Thanks again for sharing your experience. Take care, C,

[@666doll]

Hey, first of all this really helped me understand why my DIY pedals whistle and how I can get rid of (most of) it. Would it work if i connect the capacitor to the hot and the ground lugs on the DC jack?

[@sniggity]

Very helpful my friend! I’ve learned so much just by checking out your videos and reading the comments. Please keep the tutorials coming. I’ve just ordered my first breadboard from coppersound so I’ll be experimenting with circuits any day now. Thanks again 🙏🏼

[@soundpark_]

Thanks! Most pedals maker won’t tell you this tips!

[@VinceSeagal]

Thanks for this video, it's really instructive. I have a few questions if you don't mind. 1. Does the values of the input and output caps have an effect on the impedance? 2. How do you determine the best values for the filtering caps? 3. Is there any adverse effects of having power filtering in the power supply AND in the effect?

[@chipsterb4946]

The configuration you show with 2 capacitors to ground works much better with a resistor between the 2 caps to ground. This is called a Pi filter and is used extensively in tube amps. Many pedal circuits appear to use a cap and a diode to ground for filtering. I’m going to have to research that some more.

[@frederiktrikot3748]

Good video with a lot of info, thanks. Just wanted to clarify some details: at 2:16 the signal drawn is DC with noise/ripple. I believe that AC (e.g. from guitar) should get negative values (alternating). at 8:04, capacitors at series are called "coupling" cap, not "decoupling". Decoupling caps are used to separate electrical circuits and placed parallel to ground.

[@protakill]

As always, a very informative video. May you be blessed for your willingness to help mankind understand the art of DIY effects. Much respect, mate.

[@DiyguitarpedalsAu]

Thanks Protakill, hope you liked it!

[@thomashamiltom]

So when I make a vero layout for a pedal, can I just throw the caps on the vero board where the 9v goes in and send them to the ground on the board? Also, does the cap going out cause a voltage drop? Thanks again for the great vid!

[@RAndrewNeal]

If you use an inductor in series with the 9V power supply, it will resist change in current flow, and will block frequencies at a certain level and UP, instead of down like a capacitor. So it will further help reduce noise from the power supply, maybe even remove it all together.

[@DiyguitarpedalsAu]

Yes some people even solder the caps directly onto the dc jack! As long as its from plus to minus you will be fine (and the right orientation of course). Resistance (or a diode, etc) on the +9v or ground lines will cause a voltage drop, but no, caps from plus to minus will not. No problem thanks for watching and the compliment!

[@EdzusM]

First of all - huge thanks for the video! Your explanation got through to me (as opposed to some of the not so well written articles on the web I read earlier). As a newbie DIYer I have one more question. I've seen people add resistor after the decoupling cap. (for example 100k resistor after 100uf cap or 220k after 220uf cap and so on). Whats the use for that?

[@lithium122003]

I have problem when build DIY Distortion Pedal (based on IC LM386), the sound of my potentio when i open the volume to the max like a bird sound and a lot of noise (hum and buzzing). What is the problem actually ?

[@DiyguitarpedalsAu]

No problem i will try to answer. 1) i dont think so. Impedence is usually set by pull down resistors or the input of an opamp. 2) There is a calculator i used, i cant recall the name of it. The fact is though, experimenting ended up giving a better result (with the value of the cap, but also i've read since, the type of cap can make a difference as well, film and electro for exampel) 3) I dont think so. It will only filter noise, from my meager understanding anyway. Cheers

[@madmanmike7]

hello, this looks great...im just still curious about the implementation here as i couldnt get it from the drawing...wouldnt doing something like adding a 100 ohm resistor from the power supply to the pedals power input, and also adding a 220uf(or higher) cap ON the actual power jack, positive side on the power lug and the neg side on the GROUND of the power jack...?

[@keyboardjedi]

Would a full-wave rectifier also serve the same purpose? There's obviously a small voltage drop across the diodes, but theoretically speaking, isn't the behavior the same as the decoupling caps? Thoughts?

[@jakubshouseofrock7109]

These videos are great man! I was wondering why there's always capacitors on the in and output of pedals

[@DiyguitarpedalsAu]

Thanks Jakub appreciate the comment!

[@jakubshouseofrock7109]

No worries, I've been following the channel for a long time now and it's the best iv'e seen on the topic, and is what inspired me to give it ago! I'm actually trying to put together a modified version of 7 minute fuzz, and one of the features i'm looking to put into it is a switch that converts it to a Bass guitar fuzz, for that i was thinking of installing a blend control that has a pot with both a high pass filter and a low pass filter attached to lug 1 and 3 of the pot, having the bass frequencies sent clean bypassing the effect to the output, and the higher frequencies sent through the effect, so when they're combined you have the top end distorted with a clean focused low end. I'm relatively new to this so i'm not sure if this set up would work, whether the clean bass frequencies would need a boot after going through the low pass filter, and what values would work best for the potentiometer... here's a link to a detailed wiring diagram mock up I drew, scontent.fbne4-1.fna.fbcdn.net/v/t1.0-9/36659150_235620523900968_4241480023858479104_n.png?_nc_cat=0&oh=f6b38b870dc189376ed6c6e014e2df49&oe=5BD9B57C thanks so much for any advice/tips man.

[@acikast]

Thank you so much for sharing your knowledge, it means alot to me!

[@davidashford6091]

Nice explanation

[@woosix7735]

9:11 Even if you have a very stable good quality power supply, it's still a good Idea to have capacitors there: wires between the supply and circuit act as inductors, so they can actually cause the voltage to get too high and introduce some noise I think.

[@Cocolia3]

+DIY Guitar Pedals DO you have a video tutorial about fixing guitar pedal popping sound? I read the capacitor needs to be replaced with a 4.7k capacitor.

[@DiyguitarpedalsAu]

Watch my other 2 power filtering videos. I use a 100 ohm resistor as well on the plus line (well, an inductor, but i honestly didnt notice any difference between the 2). This video is specifically addressing the question about filtering guitar frequencies and the capacitors. You should experiment with the cap types and sizes to see what works for you, probably on a breadboard.

[@DiyguitarpedalsAu]

I forgot to mention it in the video but i have found that circuits that have low input impedance (ie on the transistors) usually cause the most noise (a simple transistor boost for example), where as op-amp based circuits that have a high impedance, generally dont cause as much noise. Thats what ive experienced anyway.

[@ninokolen4300]

Thanks for all the interesting clips!

[@100roberthenry]

nice one paul, great explanation . keep em coming man.

[@skylercornell7996]

Any ideas on the value of the cap to reduce the AC noise on the 9V DC line?

[@christophschuermann6512]

Skyler Cornell if you want to filter the ac signal properly, you first have to get rid of the highest HF content by using ferrite (clips, rings etc.) on both ends of your DC cable. As a 2nd step i would use a good FKP -cap of 10-100nF as close as possible connected to the DC-Input connector. Then cut the positive cable near the DC-Input and insert an inductor (100-1000uH/>=0.5A) in series and dont foget to isolate the positive Signalpath. Finally use a good electrolytic Cap. (100-330uF/25to50V Rubycon ZL, ZLH, or compareable) in parallel with a 0.1 to 1.0uF Foil Cap. directly connected to the pedal PCB. If you need help, ask a friend or go to your musicstore. Have fun with your new sound!

[@emperorSbraz]

2 ways: quick and dirty: shove a few 1000-3300uF 12-16V caps in parallel with the wire, duct tape. fancy: get yourself an LM7809 with a heatsink, make a board out of it with the caps specified in the datasheet to prevent oscillation in the chip, add a 3300uF 12V cap in parallel on the output... now you have a cheap nearly perfect 9V 1A power supply BUT you have to feed it with more than 12VDC (check LM78xx datasheet). i use the fancy one to rectify a random cheap unregulated power supply for my diy oscilloscope and it's dang good. -> imgur.com/a/3K4Mo

[@ArdiNugrohocilacap]

@@emperorSbraz its old tech.. 7809,, still great

[@Infinitychip]

Clear and well explained. Thank you.

[@DiyguitarpedalsAu]

Thanks Rob, i hope i explained it clearly.

[@Arti9m]

What's the intro music? Thanks for the video!

[@thomashamiltom]

Beautiful! I've seen this once before... Have you heard of Craig Anderton's "DIY Projects for Guitarists"? His second beginner project is just this, except that he first has a 100ohm resistor from in 9v in then a 1000uf cap going to ground... What does that do if it is indeed necessary?

[@chipsterb4946]

A resistor in line with the signal path followed by a capacitor to ground creates a low pass filter. You can look up the math to find the frequency cutoff, but a 100 ohm resistor and a 1000uf cap cuts all but the very lowest frequencies.

[@JoaoMartinsguitar]

Well, lately i´ve been studying about power supllies for pedals. And heard that for some applications a voltage regulator ic could make very big difference, it visually flattens the signal through an osciloscope. But i still have some doubts like: looking at a voodoo labs power suplly, they say that isolated outputs make big difference in power filtering because it eliminates the ground loop. Well, that means that this kind of power supply doesn´t have a commom ground?? How they can do that?? One transformer for each output?? could you help me?? Hope i make myself understandable, because i´m not a natural born english speaker.

[@DiyguitarpedalsAu]

+Joao Martins Not 100% Joao, but I think they can use either multi transformers, or a transformer with multiple outputs. Google image search "pedal power supply spyder" you will see a few examples of isolated outputs (read about this YEARS ago, but fairly certain there is a DIY project called the spyder with isolated outputs).

[@JoaoMartinsguitar]

+DIY Guitar Pedals Multiple secondaries!!!!!! How i didn´t have think on that. Thanks a lot, you have solved a mental pitfall for me. I will google your sugestion ank keep studying.

[@henryrobinson9837]

you could be a lot of help in the automotive diagnostic o-scope training or design,we have to work with both AC/DC,

[@mikep6967]

Very helpful 👍🏻

[@DiyguitarpedalsAu]

Glad it helped!

[@DiyguitarpedalsAu]

Thanks! Yep, increase input (and output) caps = More bass

[@DiyguitarpedalsAu]

Thanks!

[@mattlambert3118]

"Who is supposed to do the filtering? Is it the power supply company supposed to regulate the voltage properly or is it up to the effect manufacturer to have some sort of filtering in their circuit?" It's up the effect manufacturer. Power supplies work within the tolerance of whatever they're designed to power. If you design a circuit to use a any old non-specific power supply that doesn't necessarily meet the requirements you need it to meet, that's on you. You can't expect a company to make power supplies that are designed for doing things like powering LED strips to make them meet the requirements for an audio processing application. That would be expensive and pointless. If you aren't going to design your circuit to work well with any old power supply, you need to either make sure you can get a power supply that meets your requirements (and include it if it's a product you plan on selling) or make one that meets your requirements yourself. Advice on decoupling caps: If you need something to be really stable, put some decoupling caps in parallel. Bigger caps that hold more charge are usually slower to react than tiny ones, so get a big one that can hold all the charge required to counteract the ripple and then throw on a 0.1uF or two right next to it to pick up the slack for when the big one isn't quick enough to react. You can also throw a 10uf on if the big one is really slow and you're depleting the charge in your 0.1uF caps before the big one starts discharging. It's not quite that simple, but that should usually work even if you don't know what you're doing. When it comes to stability, you can't really have too many decoupling caps. The worst thing that can happen is that you waste a few cents and an electrical engineer laughs at you for not knowing how when enough is enough.

[@putrajagaraksa6560]

Sedih banget gw g ngerti.....

[@tubeDude48]

NOPE!!

[@wtf911wft]

The “um...uh”s keep me from even understanding what’s being said. Otherwise good video.