Help me understand popping

[Lbzg]

Hi,


I need some advice with popping when pedal is engaged. How to resolve it and what to look for to change in order to eliminate popping of pedal.

Almost all my pedals (except Distorsion + and Rebote 2.5) are popping that includes (Tube screamer 9, Rat and Microamp). I have lots of pedals to build (all parts are gathered) but I need to learn what makes pedal pop and how to eliminate it when building...

Where exactly to add a resistors and caps and what to change if they are already in circuit but are to weak to stop popping? Please I need expert advice, I will appreciate all the help but please be precise and resourceful.

P.S. I have read AMZ's guide and it is useless...does not tell anything that can help you so please no links no guides just experience and exact solutions, most of you have those pedals and have resolve this and I'm asking for your help...

Tube and Rat are from tonelab, Microamp is from GGG.

[Mark Hammer]

There are two things to understand, both of them related to the use of "true bypass" stompswitches:

1) Any sudden current draw can produce a pop.  So, when a stompswitch turns an LED on, that sudden need for current to power the LED can result in a an audible pop.  If you use a high-efficiency LED that doesn't require much current to light up then the odds of an audible pop are reduced...assuming you use a resistor that drops the current flow enough (e.g., >10k, as opposed to 2k2 or less). There is a document at AMZ that explains how to reduce the risk of pop when turning LEDs on and you can probably search for posts here too.

2) Any time you have a capacitor at either the input or output of a pedal, or even anywhere in the circuit, and one end of the capacitor is unconnected, you may experience audible popping when you suddenly connect that "free" end.

The capacitor will store charge.  How much it stores will depend on how much it is given to store, and how much storage capacity it has (i.e., .1uf has more storage capacity than 470pf, and so on).  What we hear as a "pop" is the sudden draining of stored current when the free end of that capacitor is given a path to drain off. 

The solution many use to avoid this is to stick a terminating resistor between the free end of the cap and ground.  You don't want the stored current to build up too much, so the resistance to ground can't be too high.  At the same time, you don't want to produce "loading" effects by having a terminating resistance too low.  So you will often see terminating resistors ranging from 470k to several megohms.  You don't want to go too much lower than 470k unless there is a specific reason to deliberately load down the circuit input.  AS for higher values, the smaller/lower the cap value, the higher a resistance value you can tolerate.  So, for example, a 0.1uf cap will store more chargethan .001uf.  You probably wouldn't want to go much above 1M for a .1uf input cap, but could likely be comfortable draining off whatever there is to drain from a .001uf cap using a 2.7 or even 3.3M resistor.

Because popping results from the sudden drain-off of accumulated charge, what you'll often find - even without terminating resistors -  is that after a couple of on-off presses of the stompswitch, the popping appears to go away.  That's because you have temporarily drained off the charge.  That does NOT mean it is gone for good, merely that whatever was stored up to that point has been successfully dumped.  It WILL come back.

Note that, because they do their switching "intetrnally", many pedals that use electronic switching have input capacitors with a free end.  You will hear a thump when you first plug in, but because of how they do their switching, you will not hear any popping after that, no matter how many times, or how frequently/infrequently you turn that pedal on and off.  HOWEVER, because that cap is unterminated, if you have a true bypass switched pedal plugged into it, when you hit that stompswitch, the input cap on the 2nd pedal will be momentarily disconnected from anything and reconnected, placing it at risk for producing an audible pop.  Curing this involves simply doing what Boss, DOD, or whomever declined to do: run a 1-2.2M resistor from the input lug of that pedal to ground.

ALL unterminated caps will be at risk of producing a pop when connected.  That includes more than merely input and output caps.  For example, some modulation pedals, or mods to such pedals, may suggest  a switch to toggle/select between one of several cap values, for example, to switch speed ranges on an LFO.  So, there may be one cap already in circuit, and a toggle is used to add another in parallel.  Suddenly connecting that 2nd or 3rd cap will also often produce an audible pop, for the same reasons as the input or output caps.  There are several ways to approach this: a) never flick that toggle in effect mode with the volume up, b) place several caps in series and use a toggle to select/short different ones, c) stick a high value resistor in series with the added cap to let it constantly drain, and use the toggle to short out that drain-off resistor.  You can see a good example of that latter strategy in action in the Runoffgroove Matchbox: http://www.runoffgroove.com/matchbox.html

[Gurner]

The capacitor will store charge.  How much it stores will depend on how much it is given to store, and how much storage capacity it has (i.e., .1uf has more storage capacity than 470pf, and so on).  What we hear as a "pop" is the sudden draining of stored current when the free end of that capacitor is given a path to drain off.  

The solution many use to avoid this is to stick a terminating resistor between the free end of the cap and ground.  You don't want the stored current to build up too much, so the resistance to ground can't be too high.

A capacitor doesn't store current, it stores charge (as you said initially) ...& it's abrupt changes in charge on the cap (from switching in/out other stuff)  that can cause current (or voltage) spikes...which can result in audible pops.

To avoid poppage - you want circuits/stompboxes etc to be all at the same voltage level when connecting/disconnecting to one another ...and 0V is a good universal standard(!)....so any input/output cap with a leg that's floating (due to a switch being placed in situ), ideally needs a resistor to 0V to assist in draining off an cap charge , thereby keeping the 'floating' cap leg tethered to 0V....then, when you switch stuff in & out - because everything being interconnected is sitting at 0V - there are no current spikes, so no poppage.

It's not just cap terminating resistors needed to avoid poppage (although I'd hazard a guess that it's related input & output potential differences that are the main culprits)...but good pcb layout is also key (keeping your low level signals well away from any filthy high current traces etc)

[Lurco]

http://www.diystompboxes.com/smfforum/index.php?topic=103305.msg920607#msg920607

[Lbzg]

Finaly someone to write down knowladge...and thanks lurco on my other post you answered something that wasn,t answered anywhere...those resitors should be on board...

[Lbzg]

Thanks Mark, just tell me what do you mean by '' lug '' in your post? is it lug of input jack or switch lug? and when you say that free leg of cap need to be connected with resistor and to ground which leg is it +or- leg and what with unpolarised caps... that part is very confusing...can you explain it more?

[aron]

If all of your pedals are popping maybe you have something with a dc offset going into them?

[aron]

Let's start with a simple test. Borrow some commercial pedals and see if they pop. If they do, it's not your pedals, look elsewhere. If they don't then measure and figure out what is different.

[Lbzg]

Ok, this is not possible and to be direct you didn't read my post to the end because I say that not allmy pedals pop...just ones I said...

If you have solution share it if you don't than just say that, don't imply something that have no sense at all...no offence...

I do not wish to start discussion, I just need solution for it and possible/obvious cause of problem...

We all need popping free pedals otherwise this is useless, If I know solution to some problem I share it, be sport and share it also...

[armdnrdy]

Ok, this is not possible and to be direct you didn't read my post to the end because I say that not allmy pedals pop...just ones I said...

If you have solution share it if you don't than just say that, don't imply something that have no sense at all...no offence...

I do not wish to start discussion, I just need solution for it and possible/obvious cause of problem...

We all need popping free pedals otherwise this is useless, If I know solution to some problem I share it, be sport and share it also...

Is this some kind of a joke?

I have followed three concurrent threads by this guy about the same subject. Two new threads he started and one from 2005 that he dredged up!

He has received excellent attention and information, and suggestions from forum members including one of our most respected members, Mark Hammer, yet continues to lash out with a rude, demanding tone!

All of the information/suggestions he has received is 100% valid with nothing I've read leading him down a wrong path!
No "guessing" involved here!

I believe that Lbzg needs to realize that we are helping him out of good will. This information is free. If he can't be patient enough to work with us to find the problem.....then I would say.......look elsewhere!

Sorry for the rant, but someone had to say it!

[R O Tiree]

OK, it's not a question of not sharing. It's really a question of trying to guess what the problem is when you can't get your hands on the pedals in question and physically check the build and measure what's going on.

As aron said in Reply#6, "...maybe you have something with a DC offset going into them?" You can provide anti-pop pull-down resistors until you're blue in the face, but if the input signal has a DC offset, it's going to pop as the DC component that the input cap sees suddenly jumps up. (Or possibly down? Who knows without being able to measure it?)

So, just to be extra sure, take everything else out of your signal chain and plug just one pedal in between guitar and amp. See if it pops. If not, move onto the next pedal on its own. Rinse and repeat until you find the culprit.

If you find one that pops, plug just a guitar lead into the input and a lead from the output to your amp. It will probably hum... Now short out the tip and sleeve of the free end of the input lead. Engage and disengage the pedal and see if it pops. If it does, then the problem is internal to the circuit. Remove one of the leads to the LED/resistor combo. Try again. If the pop goes away, then the LED current draw is causing the supply voltage to sag slightly, and you should use the AMZ circuit as alluded to in Reply #2 from Mark Hammer. Here is the link. This will slow down the sudden demand for current (because it gets a little help from the charge stored in the capacitor in the AMZ circuit) and the pop should reduce to a minimum.

If the pop does not go away with the AMZ mods, then that tells us that there is something more serious going on and we need to suggest which voltages to try to get readings for. As a start, I would look to see what is happening to +9V. In your original post, last line, did you mean "Tonepad"? Which layouts have you used? Exact copies of the Tonepad and GGG PCBs, vero or your own designs? Just to take the TS Tonpad layout, it already has pull-down resistors at input and output (assuming you put the 2M2 shown in red on the diagram in there? If not, then try it). I have built this particular circuit several times with several layouts (including my own) and it has never popped. Not once.

The next test is to use pairs of pedals. Find a pair of pedals that pops and measure the voltage at the "hot" lug of the Volume pot of the first pedal with the input shorted as before. (This is sometimes referred to as "lug 3" but, regardless, it's the one that connects with the wiper when the pot is wound fully clockwise). If this voltage is not zero, by even a few mV, then there is possibly a problem with the output cap connected to lug 3. Did it get fried a bit internally during the soldering process? We can't tell, really, not from behind our computer screens, but it's only one of many possible causes. Anyway, the purpose of this test is to find out whether there is a DC offset coming out of one pedal into the next one.

High-quality, well lighted, crisply focused photos of both sides of each board would be helpful... it may be that a pair of eagle eyes might spot something that doesn't look right... an incorrect resistor value, a polarised cap the wrong way round, whatever... I know these things sound almost insultingly stupid and obvious but, as RG said a few weeks ago, situational blindness is our curse (I paraphrase). We can look and look for hours, convinced we've done everything right , post a pic and some bright spark pipes up and says, "You're doing it wrong". It is in the nature of the human condition that one's first reaction will almost certainly be, "What's he on about?" followed a short while later by "Oops..."

It is no use at all insisting that you don't want a discussion about this. There is no big secret that is being kept from you. There are simply too many possible sources of this pop and they have to be eliminated, one by one. The fact that 3 of the best Tefal-heads (clever bu@@ers) that this forum boasts have weighed in on this thread is testament to their patience in trying to find out what the problem is, as they do day after day, week in, week out, year upon year. The simple fact is that there has to be a discussion to suggest tests, checks to be carried out, voltages to be measured, if the collective wisdom of this community is to have any chance of helping you through this. This also relies upon you carrying out those instructions to the letter and reporting back with results that are as accurate as you can get them.

If RG posts here, that will be 4 Tefal-heads... and if PRR contributes, that will be 5, but you will get extra homework after school. Rest assured, though, that if you carry out that extra homework, then you will definitely learn something extra.

Edit - Larry's rant is spot on, by the way...

[Lbzg]

Thanks for reply.

Led is not causing popping. Tested.

Yes, Sorry i wrote it wrong it is from tonepad. exact replica of board every pedal it is even from ggg.

I have noticed something. When I have soldered 1M + 100k + 100k in series on output jack from tip to ground popping when disangaging have stoped but it is still present when engaging pedal (when pressing on).

I have put same resistor value on input jack and nothing. Popping remains same. :-(

What values are good bigger or lower? I see that it is from voltage but I cant drain it from circuit. I cant get correct value. Any tips on that? how to exactly to measure voltage and on what part of board or pedal even to know what to do.

have someone did any kind of mod to it to stop it or not...i have put 2 x 1M on board where 2M2 needs to be since i dont have exact value but nothing have changed in popping...

[R O Tiree]

Let's start with the TubeScreamer.

Please go through the steps I detailed in Reply #10. It is not a matter of a mod that we are keeping from you. The TS on the Tonepad board should not pop. Therefore, there is something that you have done or not done that is causing this. Did you try listening for a pop with the input lead tip and sleeve shorted together as I asked?

Good quality pictures are needed, both sides, please. Make sure that they are crisp and clear, large size.

You can measure the voltage at the input end like this: Plug your guitar into the Input and connect Output to your amp. Set your meter to read Volts. If it has a mV setting, use that - it will be more accurate. Place one probe of your meter on a Ground pin on the PCB. Place the other on the junction of the 2M2 and the input cap. Engage the pedal. Look for a change in the meter reading. Now disengage the pedal and watch for a voltage change. If there is a voltage change here, then the resistor is not doing its job or the cap may be damaged.

It might be that, with the meter reading the voltage at that junction, the pedal does not pop... this is because meters have a high resistance. Some have a resistance of about 1M while more expensive ones might be well above 10M. If the pedal does not pop with the meter in place, then the meter is doing what your 2M2 is supposed to be doing. If that is so, then re-solder the joints for the 2M2. You will need some flux to ensure that the solder flows cleanly. If you do not use extra flux, the solder joint will overheat and it will either damage the components, damage the PCB tracks or go crystalline. If you're unlucky, it might do all three of those things. It might also be worth replacing the input cap completely with a new one.

It sounds as though you have sorted out the Output side of things, though, which is good. There should be no need for such a huge resistance there, but we will leave that for now.

Get me those pictures and I will have a look to see if anything does not look right.

Edit: "unlicky"... silly typo

[R.G.]

Let's indulge in a bit of basics.

@Lbzg: To understand popping you need to understand that all popping, clicks, ticks, and thumps are caused by a sudden change in the signal. Take a look:

Every sharp-edged change in level is heard as a click, pop, or thump.

Notice that the sudden change is heard as the sharpness of the change, the longer it stays away from where it was, the more low frequency "thump" is heard.

If you change levels over a time shorter than about 50mS, it's going to be heard.

Changing levels that cause noises like this nearly always come from *caps with one end opened by the switching, *leaky or wrong-way-round electrolytic caps, *DC from somewhere else that's being switched by the footswitch, or *sudden changes on the power supply or ground.

[Kesh]

just experience and exact solutions

Here is my experience and solution. I followed the AMZ guide, I always use a megaohm resistor on input and output to take DC off the caps and I use a star ground at the input jack. I have never had popping.

Sorry for the rant, but someone had to say it!

glad i'm not the only one to think that Lbzg is a wanker.

[R O Tiree]

Changing levels that cause noises like this nearly always come from *caps with one end opened by the switching, *leaky or wrong-way-round electrolytic caps, *DC from somewhere else that's being switched by the footswitch, or *sudden changes on the power supply or ground.

There you go, Lbzg - RG has summed up in one sentence what everyone else has been saying for the last 2 days. With pictures. If you do the tests that you have been asked to do exactly as they have been written down, and take some very good photos of both sides of the board and post them here, then we can help you find out what is happening. If you don't, then we cannot help.

[Lbzg]

Hi,

Guys thanks for guides and your time. I know I'm causing some nerves to tight, I apologize for that.

Here are pics.






Test with loose end of input lead shows that is problem in circuit. :-(

I will test it with multimeter and write down readings.

Also when looking at pic 2 I connect input as shown because trace was broken. :-(

[Lbzg]

I have also desolder 1M from other side for picture taking...will put it back on immediately...

[Lbzg]

I have replaced 0.027 and 10uf with 0.047 and 22uf but poppin is same...don't know what is wrong I really can't figure it out...

[R O Tiree]

OK, I have seen some problems and I have some questions for you. I have copied your picture and have put some numbers onto it. The questions/problems are in the same order as the numbers on the picture.



OK, here goes:

1.  This 1µF capacitor should not be a polarised one. The schematic and the layout clearly say "NP" next to this cap. Either get a metal-film box cap or a special electrolytic that says "NP" on the case and with no grey stripe on the side.

2.  Same as 1. Replace this cap with one of the proper type.

3.  This cap is the wrong way round. The grey stripe should be "up" in this picture, not "down". This cap has probably been damaged internally. Take it out, throw it away and replace it with a new one. This might well be the source of your popping.

4.  These resistors are doing no good at all. You have 2 x 100k and 1 x 200 ohm, all in parallel. The total resistance will be just under 200 ohms. Take that whole assembly out because...

5.  ... this resistor is your output pull-down resistor. The value should only be 10k, not 100k, but we'll leave that for now.

6.  It is a little hard to tell what the value of this resistor is. The bands should be green/brown/black/orange/brown. There is only one way to be sure - de-solder one leg and measure it. If it is 510k, you can solder it back in. If not, replace it with one of the correct value.

7.  Same as 6.

8.  This resistor should be 100 ohms, not 470 ohms. Not a big issue, though. Leave it for now.

9.  This is your input pull-down resistor. I can not see the value. Could you tell me what the bands are? Anything above 1M will be fine. It is rare for a resistor to get cooked, but it is possible. I would replace it with a new one.

10.  This cap looks a bit small for 47nF. Please report the markings on this cap.

11.  Same with this cap. As I suggested earlier, you have soldered and re-soldered the input circuitry several times and your Input track has come off. This might also have "cooked" this cap. I would replace it with a new one.

OK, that's all I could see on the top picture. The picture of the solder-side is too blurred to see anything useful. Please could you take another picture that is more clear?

Also, what is that other board in the box? People often have huge problems putting 2 circuits into the same box, so I would like you to remove that other circuit completely so we can get this one working correctly. Once that is done, we can maybe look at putting that other circuit back into the box.

Cheers.