Pop filter, reverse polarity protection and power filtering

[Jayco]

Gang,

I've been reading through various topics on pop filtering, reverse polarity protection and power filtering and would like to ask a few questions just to make sure I understand it.

Reverse polarity - I've seen both the Mosfet and the diode way of doing this... which is more common or better if I'm going to be using both a battery and a power supply?  I have some mosfets that I purchased for doing the millennium bypass circuits.. they are NTE490 mosfets.  Would those work?

Pop filtering - From what I can see with this, strapping a 2M2 resistor across the input to ground will take care of popping.  Is this ALWAYS 2M2?  Is it normally just attached to the input jack itself (from tip to sleeve)?

Power filtering - I've seen just a 100uF cap from + rail to - rail and I've also seen a 100 ohm resistor thrown before the cap on the + side.  I assume the 100 ohm resistor cleans up noise on the power line slightly and that the cap is meant to handle variations in power?  Is this normally attached to the circuit board, or does anyone attach this directly to the power jack?

Sorry for all the questions, I've never done any of these things before (polarity protection, pop and power filtering), but want to do it right in the pedals I am starting to build.

Thanks,
Jim

[petemoore]

Gang,

I've been reading through various topics on pop filtering, reverse polarity protection and power filtering and would like to ask a few questions just to make sure I understand it.

Reverse polarity - I've seen both the Mosfet and the diode way of doing this... which is more common or better if I'm going to be using both a battery and a power supply?  I have some mosfets that I purchased for doing the millennium bypass circuits.. they are NTE490 mosfets.  Would those work?
  I use a diode from ground to V+...EZ...IIUC I'm losing one diode drop worth of voltage that way.
Pop filtering - From what I can see with this, strapping a 2M2 resistor across the input to ground will take care of popping.  Is this ALWAYS 2M2?  Is it normally just attached to the input jack itself (from tip to sleeve)?
  2m2 should do unless your caps are really leaky, 1m works fine, lower values do that, so does a standard 100k volume control with the cap 'inside' cct. you may notice loading effect as lower values are used to drain the 'pop' charge out of the caps.
Power filtering - I've seen just a 100uF cap from + rail to - rail and I've also seen a 100 ohm resistor thrown before the cap on the + side.  I assume the 100 ohm resistor cleans up noise on the power line slightly and that the cap is meant to handle variations in power?  Is this normally attached to the circuit board, or does anyone attach this directly to the power jack?
  Not sure how, but it works...the 100ohm turns it to more of a voltage source? thereby causing the peaks to be 'absorbed' by the BFC?
Sorry for all the questions, I've never done any of these things before (polarity protection, pop and power filtering), but want to do it right in the pedals I am starting to build.
 
Thanks,
Jim

[Jayco]

Pete,

Thanks for the reply.  Any particular diode that you use for the voltage drop?

Do you mount your power regulating cap right on the power jack, or do you put it on the pcb?

Jim

[petemoore]

Pete,

Thanks for the reply.  Any particular diode that you use for the voltage drop?
  1n400x [4001, 4007 etc.] Basically any big 'ol diode that measures an Si's voltage threshold on the 'ol DMM...
  Do you mount your power regulating cap right on the power jack, or do you put it on the pcb? Actually on the perfboard...close to the circuit from what I understand...some circuits are pickier than others...from what I understand by reading 'put the filter cap right next to the chip'...but I forget what the exact circuit that was referred to for that...I'd guess for a Fuzz on the power jack'd be ok..[?]

Jim

[Mark Hammer]

The terminating resistor on the input has to be small enough for the cap to be able to drain off all charge, yet big enough that the circuit would rather "see" what's coming from the input jack than what's coming from that resistor.  If you knew definitively that you would never ever plug anything into that pedal that had an output impedance greater than 1k, I imagine you could do fine with a 470k resistor (or less!), but since you might be plugging just about anything into it, we lean towards a larger resistor to anticipate worst case scenarios. 

As long as the input cap has a path to ground, it can drain off.  The question is "How fast?".  When you engage the circuit, connecting the input jack to the input cap, that cap has a path to drain to ground via whatever you've plugged in.  If there is little charge stored in that input cap, AND the existing path to ground is low enough resistance, AND the cap has long enough to drain (i.e., you don't engage the effect very often), then you won't hear a pop as the cap suddenly "discovers" an express route to ground when you engage the effect.  If it's a big cap (e.g, 10uf) and we expect to be engaging the effect often enough that it will never be quite fully drained before the next switch contact, then we'll need to give it a fighting chance by reducing the size of that dran resistor.  In the perfect scenario, we could probably stick a 10M resistor in there and be fine.  But for worst-case scenario we'll scale down and recommend something between 1M and 3M3 (favouring 1-2M).  The "ideal" resistor value is based on a set of needs, and a set of unknowns.

The RC pair and power filtering...

You know that 1k/.22uf combo after the clipping stage in the Tube Screamer?  It is to roll off the highs and "smooth out" the clipping.  The tiny resistor/large cap combination on the power line does the same thing.  If you had a 100R/470uf cap combo, that would actually provide a lowpass filter, rolling off above 3.4hz.  That'll do a pretty good job of taming 60hz hum.  The large cap not only "smooths out" any ripple in the AC-to-DC conversion, but it stores charge to supply a little extra current for brief transients.  The resistor helps to set the rolloff and degree of filtering, but it also limits the amount of current that can pass to the circuit.  You don't want it to be too large or the circuit will be "starved".

[Jayco]

Mark,

Much appreciated!

That makes much more sense to me now... and looks like the values I had (found from other posts) are at least useable if not even recommended.

Great.

Is there any problem with taking the pop-filter resistor and putting it directly on the input jack between the tip and sleeve connectors?  It would seems that since those are the connections (input and ground) we are dealing with, that it would be a logical place to do it consistently without modifying the actual pcb schematics.

Likewise, I would think the power-filter cap could go between the lugs of the actual power jack.

Jim

[bioroids]

Is there any problem with taking the pop-filter resistor and putting it directly on the input jack between the tip and sleeve connectors?  It would seems that since those are the connections (input and ground) we are dealing with, that it would be a logical place to do it consistently without modifying the actual pcb schematics.

You can't do that, because when the effect is bypassed you want the pull down resistor to be connected to the input cap (and same with the output) and that will not happen if you connect it directly at the input jack.

Luck

Miguel

[formerMember1]

i know how to do all that already and have done it,..i also see threads like this come and go,..but one thing remains unanswered for me,..

My wah never popped, now with a LED it pops, i have seen threads about LED causing pops, but never find  solution,..i guess there is none,..

3pdt switch used, middle and left colums for circuit, and right colum of lugs used for power switching the LED, would lessening the brightness of the LED lessen the pop, since less power would be being switched?

I guess maybe i should convert my wah to grounded input TB instead of ordinary truebypass?

WHat would i do to make the wah grounded input TB, would it make the LED POP go?

here is a pic of the switch in my wah,..



thanks for any advise,..

[Mark Hammer]

The only thing I can think of is that the LED and accompanying current-limiting resistor require too much current, such that the sudden surge towards the LED is felt on the audio power lines the same way a surge from an LFO causes audible ticking.

Two things to consider. 

• Change over, if you haven't already done so, to a high brightness LED, maximize its visibility (black bezels work better than shiny chrome because of the higher contrast between LED and surround), and increase the series resistor as much as you can tolerate (increasing resistance will decrease brightness) to reduce current consumption.  Less current demand from the LED part of the circuit should reduce the audibility of any popping.  Good for batteries too.
• Decouple the LED part of the circuit.  Yeah, I know that a resistor and an LED isn't much of a "circuit", but if it screams "Me too!  Over here!  Over here!" when the power gets connected, then it counts as a circuit.  If you woud stick a resistor in series and a cap to ground to decouple other semiconductors, why not the LED?  What I'm thinking is a 10uf cap (or thereabouts) to ground from the junction of the resistor and LED, making sure to observe proper cap polarity (neg to ground).

[formerMember1]

Yeah, the LED R is 1k, i normally use higher, but the purpose of this LED, is to show it is on, but also to shine light across my pedalboard, it works, good, if i am ever inbetween a song, and have to change/check a pot on another pedal, i turn on the wah, and it glows my pedalboard, enough to allow the knob posisitons to be seen,...escpecially in dark clubs,...

I will try the 10uf cap,..to ground,...and if not, i will higher the LED resistor,..or both

BTW, the resistors is a high bightness BLUE LED, water clear, but the LED is sanded with 600grit to be diffused almost,...I always use RED, but the blue is better for lighting the pedaboard on a wah,....

THANKS!!! 

***EDIT***

Just remembered something,...THe felt is removed from the wah, so the switch is being hit by the wah enclosure, not by a rubber shoe like other pedals or felt pad,...i noticed if i bend down and push the switch with my thumb, the POP isn't nearly as loud, i thought maybe it was the CLANK from metal to metal, but am thinking maybe the metal switch is hitting the enclosure causing some POP or something from power to ground(enclosure),..but probably not,...

[Mark Hammer]

Just occurred to me that the cap to ground will introduce lag in the illumination of the LED.  On the one hand, that might eliminate sudden supply shifts and reduce popping, but on the other hand, that can also cause the LED to take a moment to darken, leading the user to think the switch was not pressed.  So try sticking a 100k resistor in parallel with the cap to drain it off quickly when you go to bypass.

[formerMember1]

thanks Mark for that followup, that was nice that you cared enough to think of it, then find the thread and post a followup   

I didn't get a chance to do the "mod" yet, some things came up this weekend that ended up requiring all my time,..but this week i am going to do it,... i have to,... the pop can't stay.

I will report back on the outcome   

[formerMember1]

Hey Mark,

I highered the LED resistor to 2.2K and also tried a 100uf and also tried a  220uF electro to ground from where the resistor connects to the LED.  THe electro just made the LED blink, (enough of a BLink to annoy ya everytime you turn it on).

I don't know what else to do.  I even switched the wah to grounded input truebypass wiring.  I am thinking if i use split bypass it will stop the LED pop.

THe wah only pops if i have a fuzzface, rangemaster or TS9 on after it.  If just into a clean amp it is quiet.  I didn't try it on a cranked hafl stack though, it might pop then even with no other dist/fuzz pedals ON.

My Rangemasters and Fuzzface's POP with a LED also.  I am thinking if you use an LED there is no solution to stop popping.

My circuit board does make alot of noise in the amp if i tap on it.  I am thinking maybe my Inductor is causing that, but i think all wahs do that...

Anyone can help please do. ;-)

Does anybody else have POPs from an LED that they can't get rid of no matter what?  I think i read on analogmans site that sometimes an LED pop is unavoidable.

*edit*
forgot to mention the wah only pops when turned ON, when turning OFF there is no POP....

[R.G.]

This comes up over and over.

LEDs are current hogs. Typical LED indicators use currents that may be more than the entire rest of the circuit.

Especially when you switch an LED by a mechanical switch, it goes from off to on instantaneously. There is an instantaneous change in the currents in the wires leading +V and ground to the LED. The wires, being as they are only low value resistors, change their voltage instantaneously. If the effect circuit shares any part of the power wiring, including especially the ground, you have a good chance of popping.

If you have set up the input jack stereo trick for power switching, you have built the LED pop in. That funnels 100% of effect plus LED current through the same wire that the input signal shares. The input signal will usually be amplified by the effect circuit. So will the LED transient. If you have a distortion pedal after the one that's causing the pop, the pop is amplified by the distortion pedal.

LED pop is not caused by capacitor leakage, and so it's not cured by pull-down resistors. It's cured by better wiring.

Another trick is to split the LED resistor in half, and hook a largish value electro cap from there to ground. Done properly, this slows down the rate at which the LED current changes, and slows down the pop edge, which usually makes it unnoticeable.

[formerMember1]

thank you 

i figured it came up often but i could never find it on the forum when searching for months now, i would find talk about it but no solution.  I knew the pulldown had nothing to do with it and i tried that capacitor trick but it didn't work for me, it just made it blink.  I had thought the grounded input wiring would have fixed it, but it didn't.

i will try highering the current limiting resistor even more.  It is at 2.2k with a high brightness BLUE LED, that has the lense sanded for better viewing angle. The reason i made it so low and bright is the LED is on the side of the wah, so i only see the side of the LED, not looking straight down at it like in a normal pedal so it is hard to see to begin with.  I don't want to remove the power stereo switching trick though, for the occasional jam/gig when i use a battery.

as far as better wiring, i thought my wah was wired best it can be already, i kept the input and output seperate and neat, but i guess you mean the power switching trick.



But you mean if i DO move the ground wire of battery from the ring to the sleeve, thus getting rid of the "stereo jack power switching trick", the LED pop should go away?  Thinking about it that should be fine becuase i mainly use a power jack, but when i occasionally use a battery, i will just make sure to remove the battery when not using it, instead of removing the input jack cord.( or just add a toggle to kill the battery)

thanks again....

[formerMember1]

I tried removing the stereo power switching trick and that didn't help at all.   

I am thinking maybe it has to do more with the Halo inductor being microphonic or something.  When i tap on the board there is alot of noise.  Also i had to put felt to stop the switch from touching the enclosure cuz that caused alot of noise through the amp.  so i think it is a combonation of both, also my other pedals pop from the LED, so it isn't just the inductor doing it.

***EDIT***

I just removed the LED completely and the wah still POPS.  It also makes alot of noise if i touch the enlcosure/board with my fingers, i could hear my finger pad rubbing the enclosure, tapping it etc,...

What could be causing this?

Can it be the grounded input wiring?

I think it is the Arielfx Inductor doing it.  Like i said, with a fuzzface or something on after it, it is really bad....

anyone ever have this before?

I'll keep searching,...

[formerMember1]

Ok to update..

I still have pops in the wah when i turn it On, but not off.  I have actually built another wah, with non truebypass(just to try to get it to not pop!), using a 3pdt and it is wired for input never bypassed.  It POPS when i have a fuzzface or RM or TS9 or anyhting On after it.  It is driving me nuts. 

It isn't as bad as the wah with the LED, but it still POPs bad enough to be very annoying and impossible to record with.  I though non truebypass would have made it not pop?

Could it be something with the other pedals that is making the wahs pop somehow?  The fuzzface and RM pop too, and they have pulldowns and stuff,.. etc...

I don't know why all my pedals pop, it is very annoying...

I have searched the forum many times and never really find a solution to the problem.... sounds silly, but i can't get rid of these pops...

I have tried battery and power jack.. pulldowns, caps and resistors going to LED and stuff.. everything i can find in a search and prior post

any advice?  Anything i could do to find out what is causing the pop?

*EDIT*
a wah expert out there has told me it may be the switch,.. but i have tried SPDT's and 3PDT's...

[aron]

So the wah always pops when a Fuzz Face is after it?

Did you try measuring the DC voltage out of the wah? I know, this popping problem is a pain. This could be made worse by the hi-gain pedal (fuzz face) after the wah. Maybe it pops just a little, but the fuzz pedal makes it worse?

[petemoore]

  Jayco Asked:
  Is there any problem with taking the pop-filter resistor and putting it directly on the input jack between the tip and sleeve connectors?
  I often install them right on the switch, to the circuit input lug, then connect my input wire to the resistors lead.

[formerMember1]

So the wah always pops when a Fuzz Face is after it?

Did you try measuring the DC voltage out of the wah? I know, this popping problem is a pain. This could be made worse by the hi-gain pedal (fuzz face) after the wah. Maybe it pops just a little, but the fuzz pedal makes it worse?

yeah, see all my pedals POP.  I could never stop them from popping.  THe POP did reduce when i used the right set of lugs on the 3PDT instead of the center though, but the POP is still loud. 

The wah only POPS when I turn it ON. I don't notice it popping without a fuzzface on after it, or a TS9 or rangemaster etc...  The reason i posted about it again, was i always thought it was the LED. BUt then i removed the LED and it still popped.  I then thought it was a microphonic inductor, but i tried 3 different inductors and always the same thing.  I now built  a wah with a 3pdt but made it non truebypass,.. same wiring as the old wahs, with input never bypassed.  ONly an output buffer, no input buffer and it pops with a fuzzface on after it.  R.G. said the fuzzface is amplifying the POP.

I will measure the dc voltage then on the switch, and see if maybe my input cap is leaky or something... i don't think it is the cap though, becuase i swapped it numerous times and every wah(3 wahs) pop and they all have different caps...

Teese told me it may be the switch itself popping, so i changed the switch.  It still pops.  I had a SPDT carling in my other wah pedal, wired the same way and that pops, so i don't think it is the switch.

I don't know what to think....

my fuzzface and my RM's pop too... they have LED's and i removed them and they pop.  I tried pulldowns and electro caps and no luck... I have a 100uF filter cap in the wah, i will try a 220uF... but that shouldn't be it becuase it tried a battery and it pops...