60 cycle hum

[instantaphex]

So I've got my first build breadboarded and according to schematic, pin 3 of the presence pot isn't hooked up to anything.  So I left it unplugged from everything and now unless I am pinching the end of the lead with my fingers, I get a 60 cycle hum.  Anyone know how to fix it?  I would post more info, but I'm not even entirely sure what is relevant in this case.  BTW thanks a lot guys for all your help.  It's such an awesome feeling to hear the sound of an overdrive I just put together myself. 

[pappasmurfsharem]

Have a link to the schem?

NOt sure if it applies here but sometimes the lug may be tied to the center lug to create a variable resistor versus a voltage divder. aka lug 2 and 3 MIGHT need to be connected together.

[instantaphex]

Here is the schematic I built it from:

EDIT:  See below

Other than the 60 cycle it sounds great.  The pot in question is the 5k linear presence pot.

[instantaphex]

Sorry about that.  Here it is

[gjcamann]

I get a ton of hum in my breadboards too. I think it has alot to do with not being in a metal pedal box and long jumpers acting like antennas. I would guess it would go a way if you boxed it. (But to be honest - I still have yet to box my first pedal). Maybe someone can confirm this.

When you touch any part of the circuit, it acts like putting a large resistor (1uF) and capacitor (1M) to ground. You could try that?

Have you tried disconnecting the presence circuit to see if it goes away?

EDIT: Confirmed http://www.diystompboxes.com/smfforum/index.php?topic=104542.msg937614#msg937614

[Kipper4]

Did you try connecting lug 3 to lug 2.
Thats where i'd start.

[instantaphex]

I did suspect that maybe an enclosure would fix the problem but I wanted to be sure before soldering everything together.  I haven't tried connecting lug 2 and 3 together.  It never occurred to me.  Is that a common practice?  I say a layout for this on tagboard effects that had a 47uF cap connected to power.  I didn't see that in the schematic.  Could that have something to do with it?

[induction]

Yes. That should help a lot.

If the cap alone doesn't entirely remove the hum, a regulated adapter usually will.

Have you tried it with a battery? If it still hums with a battery, it's something else.

[instantaphex]

Yes. That should help a lot.

If the cap alone doesn't entirely remove the hum, a regulated adapter usually will.

Have you tried it with a battery? If it still hums with a battery, it's something else.

Actually, I've been using a battery.  I haven't quite figured out how to hook up the AC adapter yet.  I desoldered a jack from a TS7 and haven't tried hooking it up.  There are 3 pins.  Do two of them go to ground?

[Pojo]

Is the power cord for the amp properly grounded? (ie, 3 prong power cord, not using a ground lift 2 prong adapter at the outlet). This doesn't seem to be related to your pedal since you're running battery power. Your pedal may very well be amplifying the noise though.

Another possibility is RF from fluorescent lighting, etc.

Yes. That should help a lot.

If the cap alone doesn't entirely remove the hum, a regulated adapter usually will.

Have you tried it with a battery? If it still hums with a battery, it's something else.

Actually, I've been using a battery.  I haven't quite figured out how to hook up the AC adapter yet.  I desoldered a jack from a TS7 and haven't tried hooking it up.  There are 3 pins.  Do two of them go to ground?

No. One goes to ground, another is the positive supply voltage, the other takes the + from the battery snap. When you plug the supply cord in the jack, the jack works as a switch and the + from the battery is disconnected from the circuit so that you can use the voltage from the adapter without draining your batter. When you remove the plug the jack connects the the battery + pin to the positive supply pin allowing the battery to power the circuit.

[MrStab]

unless I am pinching the end of the lead with my fingers, I get ... hum. 

i hate to be clichéd, but my instinct says "ground". definitely not mains hum. ground problems don't always sound intense and obvious, in my experience - they can be more subtle. if i were in your shoes, i'd just hunt for grounding issues - they can sometimes be sneaky and happen in unexpected ways, and if it's not a ground issue, at least you'll have ruled it out. worst-case scenario, you could just expand upon what George said and use a cap/resistor to ground to make an "artificial finger" in the offending area lol.

[instantaphex]

unless I am pinching the end of the lead with my fingers, I get ... hum.

i hate to be clichéd, but my instinct says "ground". definitely not mains hum. ground problems don't always sound intense and obvious, in my experience - they can be more subtle. if i were in your shoes, i'd just hunt for grounding issues - they can sometimes be sneaky and happen in unexpected ways, and if it's not a ground issue, at least you'll have ruled it out. worst-case scenario, you could just expand upon what George said and use a cap/resistor to ground to make an "artificial finger" in the offending area lol.

Maybe so.  This being my first build I can't say for sure.  It disappears completely when I turn down the knob just a bit.  Maybe the pot value is off?  Like I said, I've been using a battery if that makes any difference.

[mistahead]

I'd shield up, put a metal bowl over the thing to reduce the amount of possible EMI and see if it reduces the hum - shouldn't need anything trickly but clip a gnd to the bowl if you are really keen.

All you want to do is reduce external sources (battery is isolated power, I'm guessing you can't switch amps for testing?) of EMI for the sake of ticking an easy thing off the list before you go nuts chasing ghosts through dodgy hydroponics setups... I mean badly wired houses.   

[instantaphex]

I'd shield up, put a metal bowl over the thing to reduce the amount of possible EMI and see if it reduces the hum - shouldn't need anything trickly but clip a gnd to the bowl if you are really keen.

All you want to do is reduce external sources (battery is isolated power, I'm guessing you can't switch amps for testing?) of EMI for the sake of ticking an easy thing off the list before you go nuts chasing ghosts through dodgy hydroponics setups... I mean badly wired houses.   

This is probably a good idea.  Testing is not possible now as I think my op amp may be fried (see my other thread).  But I also just realized something... I've been sitting in front of my computer playing with this thing.  A lot of times when I do that, I get a wicked hum.  I won't know if that fixes it until I figure out why I'm no longer getting sound 

[mistahead]

CRT monitor or TV attached to the PC.   

[instantaphex]

CRT monitor or TV attached to the PC.   

Nah, I don't have a CRT or a TV attached.  I just always get a hum sitting at the computer.  It just sounded a bit different with this circuit.

[gjcamann]

Fluorescent lights?

[MrStab]

It disappears completely when I turn down the knob just a bit.  Maybe the pot value is off? 

the hum disappears or the whole sound does? it's most likely not gonna be caused by the pot value. is lug 1 definitely connected to ground? it's rare to need to in my experience, but it may be worth trying another pot. you can probably sub a 10K in there if you have to.

[instantaphex]

It disappears completely when I turn down the knob just a bit.  Maybe the pot value is off? 

the hum disappears or the whole sound does? it's most likely not gonna be caused by the pot value. is lug 1 definitely connected to ground? it's rare to need to in my experience, but it may be worth trying another pot. you can probably sub a 10K in there if you have to.

The hum disappears.  The circuit sounds awesome before the last little bit.  I'll probably end up swapping out some of the pots anyways since a couple of them don't seem to have a great range.  Lug 1 is connected to a film cap that goes to ground.  I put a 20k in there instead of a 25k.

[gjcamann]

It disappears completely when I turn down the knob just a bit.  Maybe the pot value is off? 

the hum disappears or the whole sound does? it's most likely not gonna be caused by the pot value. is lug 1 definitely connected to ground? it's rare to need to in my experience, but it may be worth trying another pot. you can probably sub a 10K in there if you have to.

The hum disappears.  The circuit sounds awesome before the last little bit.  I'll probably end up swapping out some of the pots anyways since a couple of them don't seem to have a great range.  Lug 1 is connected to a film cap that goes to ground.  I put a 20k in there instead of a 25k.

Maybe it's a bad pot that is going open circuit during that last little bit - causing that connection to float. If you tie the two pot lugs together, it would fix this problem without having the replace the pot.