Wah/boost making ground-y noise (but only w/ fuzz??)

[MechaGodzilla]

I built a boost into the output of my wah and it sounds great except when I run it with my fuzzface clone.

It came out of an experiment where I was running wah > sho > fuzzface where the sho was acting as a buffer to stop the wah/fuzz oscillation thing. It sounded wicked so I thought "I'll buildan sho buffer/boost into the wah" so I did.

BUT NOW, IT'S NOISY FOR SOME REASON???

it sounds like ground noise underneath the guitar sound and it only happens when the wah is on with the fuzz. without the fuzz, it sounds fine.

smart people, please tell me, what do i do to fix it??

[BetterOffShred]

Does it happen fuzz face --> wah? I know fuzz face variants like to be first .. just an idea. Then if it still does, maybe try some built in power filtering like a huminator or something..

Are you saying when it was all three circuits separate it wasn't noisy, but with the 2 combined in the wah it is?

Interesting

[MechaGodzilla]

Are you saying when it was all three circuits separate it wasn't noisy, but with the 2 combined in the wah it is?

Interesting

exactly. I can't think what the problem could be. Are there lead dress tips I could try to see if that helped? shielded wire?

[crochambeau]

How are your formerly separate grounds and power rails connected to one another in the single enclosure? Regarding ground reference, are there additional links based around signal path, or did you simplify where you could?

I'm ASSuming the unwelcome noise is constant like a ground loop and does not change frequency as you actuate the wha.

[MechaGodzilla]

How are your formerly separate grounds and power rails connected to one another in the single enclosure?

It's just running off a battery. The red + goes to the wah board and then I took the boost v+ from that. The battery black- goes to the stereo input jack and connects to the chassis ground point. The boost ground goes to the top left lug of the dpdt switch, which then goes to ground.

Should I just connect it to the chassis ground? Is there a problem with powering it this way?

Regarding ground reference, are there additional links based around signal path, or did you simplify where you could?

The boost circuit only has one ground connection on the pcb and I sent that to ground through the switch

I'm ASSuming the unwelcome noise is constant like a ground loop and does not change frequency as you actuate the wha.

yeah, it's like hearing an unplugged buzzing jack alongside the guitar sound.

here's a pic of what's going on in there


I don't know how but could it be a problem with polarity? I'm pretty sure the fuzz is PNP and the wah is NPN, which isn't an issue for the boost mosfet bs170 but perhaps they don't want to be friends for some reason?

[crochambeau]

Before we dig too deeply into the wah/boost as being culprit, can you recreate the hum with any other fuzz or high gain pedal?

It's just running off a battery. The red + goes to the wah board and then I took the boost v+ from that. The battery black- goes to the stereo input jack and connects to the chassis ground point. The boost ground goes to the top left lug of the dpdt switch, which then goes to ground.

Should I just connect it to the chassis ground? Is there a problem with powering it this way?

My only concern here is the complex circuit the ground is facing. I would connect to chassis at one point (it'll happen through the stereo jack) and consider that a shield that should not be burdened with carrying any circuits. The ground/v- of each circuit board I would connect to the sleeve connector of the TRS with battery negative being on ring for the power disconnect. I don't know what function the DPDT switch is performing in relation to ground though, if it's bypass to fire an LED I would simply tie that (the ground feed to switch) into the sleeve of the TRS as well. Though if you've got a solid connection between the v- of your boost circuit and ground it's probably no concern.

I'd also hard wire the sleeve of the input jack to the sleeve of the output jack (and I'll use either jack as the sort of "master" ground plane, since battery powered stuff typically isn't really current hungry).

I'll admit, I would be more concerned about the current path in this area if the unit was powered from a PSU (which also fed the fuzz), but it sounds like that's a concern that does not exist here.

I don't know how but could it be a problem with polarity? I'm pretty sure the fuzz is PNP and the wah is NPN, which isn't an issue for the boost mosfet bs170 but perhaps they don't want to be friends for some reason?

You're talking about two different circuits, each inside their own enclosure and powered by their own battery, true? Should not be an issue.

Could be a high impedance on the ground plane between the two pedals, brought on by a bad or dirty jack or faulty cable. Have you a multimeter? Plugging cables into the wah, on into the fuzz, and out of the fuzz you should be able to measure the resistance between the sleeve of the first-most cable and the sleeve of the last cable and observe a figure as close to zero as possible.

[MechaGodzilla]

Yeah it's like [0.]7 ohms measuring across the sleeves, that seems pretty negligible. All the ground connections have decent continuity and I don't think there's a loop

I tried the ssbs buzzz (about the highest gain fuzz I've got) I get the same sort of noise but not as invasive or problematic as with either of my fuzz faces.

but... why would it be fine with a standard SHO, but not with this crackle-not-ok boost inside the wah??? I don't know enough about this stuff to even work it out.

Alright, I got it finally figured out... an SHO-style MOSFET boost with NO CRACKLE!!!
I came up with a new gain control for it that allows for the same range of gain adjustment without having to adjust the Source. Since the Source stays fixed, there is no crackling.
While thinking about how to solve this problem, I realized I could treat the basic gain stage as an inverting opamp. So, I set a fixed max gain and tried a variable resistance in series with the input and voila, works perfectly.
Check it out and give it a try; it's a great improvement over the SHO and it's easy to tweak the sound to taste.

[crochambeau]

Yeah it's like 7 ohms measuring across the sleeves

I just measured 0.3 ohms across four pedals daisy-chained. I'd narrow down where your surplus resistance is coming from, "short" that, and see if the problem goes away.

[MechaGodzilla]

sorry, it was .7 ohms

[crochambeau]

Ah, shoot. I thought we were on to something there.

What does the front end of the following fuzz look like? Does it have a bleeder resistor to ground or are you shoveling signal right into the transistor base and calling it a day?

[eatyourguitar]

I'd also hard wire the sleeve of the input jack to the sleeve of the output jack (and I'll use either jack as the sort of "master" ground plane, since battery powered stuff typically isn't really current hungry).

this is the only part I would disagree with you. I would tie them together if they were plastic jacks or if I had star grounded everything with no battery. when you have a TRS input jack and everything is connected to something that is connected to something that is connected to ground is exactly how the problems start. I never wire the battery (-) to chassis ground. I wire the battery to the ring and only the ring. the input sleeve becomes the place for star grounding everything. I use sand paper to remove oil, dirt, and oxide buildup on the parts of the enclosure that need low resistance metal on metal contact with the jacks. I have never measured an enclosure that was more than 1 OHM resistance. good enough for me. it looks like they used the chassis as a bus bar. I wouldn't because they are all using a different places on the chassis. the chassis should be treated like an aerial. therefor it should be grounded at one end and it should carry no current from anything that is not an aerial. the obvious exception would be that the output jack sleeve is carrying signal and referencing chassis ground at the output. this is unavoidable but it does not cause problems since it has a single path to the single ground reference at the input jack sleeve.

and don't forget to put a 100R, 10nF, 10uF in the power input of the PCB. standard RC lowpass power input filtering.

[crochambeau]

I'd also hard wire the sleeve of the input jack to the sleeve of the output jack (and I'll use either jack as the sort of "master" ground plane, since battery powered stuff typically isn't really current hungry).

this is the only part I would disagree with you.

I'm curious, are you disagreeing with tying the output jack sleeve to the input jack sleeve or just the part about treating the ground connected output jack as a suitable ground reference tie in point?

I'll grant the latter aspect is borne in laziness (and/or striving for a cleaner install); the former I'll stick to my guns on however. I've seen multiple builds that complete ground reference through the chassis only on a jack and that "system" almost always suffers abuse and corrosion over time.

and don't forget to put a 100R, 10nF, 10uF in the power input of the PCB. standard RC lowpass power input filtering.

Agreed. One for each separate circuit inside the enclosure, in case this was not clear.

[BetterOffShred]

I always use a huminator on multiple circuit stuff.

[eatyourguitar]

I'm curious, are you disagreeing with tying the output jack sleeve to the input jack sleeve or just the part about treating the ground connected output jack as a suitable ground reference tie in point?

when you use the case as a bus bar for the output jack sleeve and only the output jack sleeve, the output jack sleeve is actually referencing ground at the location of the input jack sleeve since everything is star grounded (including power entry and power distribution) to the input jack sleeve. the problem would be if your battery was on the input ring, the pcb power is the output sleeve, this is bad. now if you have plastic jacks, you have no chassis ground to use or abuse so there is really only one way with plastic jacks and hopefully it is also star grounded with plastic jacks.

to sum it all up
1. star ground everything always
2. avoid ground loops and parallel ground conductors especially if they are different length, different resistance, different capacitance and lots of current being consumed.
3. use low impedance (low resistance) conductors and shortest wire possible for ground connections.

about the jacks developing oxidation that may impede the low resistance metal on metal coupling, I have never seen this happen but I can agree that anything is possible. you can predict these chemical reactions precisely by examining the relationship of the two metals on the galvanic series. I always use a shit load of force to torque down the jacks. I actually want them to press into the metal and pierce the oxide. I always sand them down before I build them for chassis ground to prevent oxide and oil from being a thing at the time of manufacturing.

[MechaGodzilla]

I always use a huminator on multiple circuit stuff.

I was gonna order some diodes to try this (might anyway) but it seems it's mainly for reducing noise from PSUs or dirty mains supplies? This unit is battery only.