[first build] Fatpants noise issue - grounding?

[thebigkevdogg]

Hi All,

I just completed my first build, Fatpants 2012 edition (no mods or swapped parts). I think that it sounds great, but I am getting some swirly noise whenever the pedal is engaged. I have uploaded a youtube video demonstrating the problem:

I didn't quite know what I was doing with grounding so maybe that's the issue? I tried another 3PDT switching diagram but that didn't help. Or could it be a bad component somewhere? I adjusted the trimpot so that I get exactly 9V over Q2 so I don't think that's it. Any advice would be much appreciated. Also as you can hear from the video I'm getting a lot of "pop" when you engage the switch.

Thanks!

[thebigkevdogg]

I had some time tonight so I poked around with an audio probe. The noise is introduced right at Q2. I replaced it with another J201 and it reduced the noise to a usable level. The swirly sound is still there, just not very noticeable at unity gain (it is definitely noticeable at higher boost levels though). Any tips on reducing it further? Other than that I am incredibly happy with how it sounds!

Also, the body switch seems to add a lot of volume, is this normal?

Thanks for your time!

[gtr2]

Yes, something is wrong.

You should not have pops like that or the white noise.

Post up some voltages of the IC and transistors.  Also make sure that lug 1 on the level 500k pot is indeed grounded by checking continuity between the lug and a gnd point.

Josh

[midwayfair]

I had some time tonight so I poked around with an audio probe. The noise is introduced right at Q2. I replaced it with another J201 and it reduced the noise to a usable level. The swirly sound is still there, just not very noticeable at unity gain (it is definitely noticeable at higher boost levels though). Any tips on reducing it further? Other than that I am incredibly happy with how it sounds!

Also, the body switch seems to add a lot of volume, is this normal?

Thanks for your time!

The Fatpants I've built are pretty quiet, but it's a little odd that swapping out the FET made it quieter. If you're using sockets, make sure everything's got good contact. A little dab of solder on each pin might be necessary. Make sure your soldering underneath the board is good.

Also, even though the pedal has power filtering, you could have an issue with your power supply. Some 9v power supplies make noise with gain effects, but I don't know the specific circumstances that it happens. I do know something like a one spot or boss adapter doesn't have the problem.

The switch pop is caused by DC buildup. Since this circuit has a pull-down resistor, if the resistor isn't working, that again leads me to suspect something is generally wrong in the grounding and/or power, possibly a small solder bridge. Hard to say without pictures or voltages.

The crackle when turning the knob IS normal as noted in the build doc.

[thebigkevdogg]

Thanks for the reply guys! I had another fatpants board for another build (this time integrated with another pedal) so I went ahead and built that for comparison. It is perfectly noise free, so now I have a reference when comparing voltages and such. I think I can take it from here but will report back if I can't figure it out.

[Om_Audio]

That pop sound sampled, detuned and combined w orig sample would make a great rhythm/drum sound.
Hope you sort it out- def report back when you solve it.
C