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I dont know how to check it against the schematic

Reading a schematic is a necessary skill to develop.
http://www.beavisaudio.com/techpages/SchematicToReality/

A layout is not a schematic, and there is no substitute. Now's a good time to learn. Break the schematic down into very small sections. If you get stuck, I and many others here will be happy to help. (But I think you have to try on your own first!)

Heh, nice.

I draw the line at DIYing anything that can blow the house up. I am forbidden to get a soldering iron anywhere near the heater, for instance.

Could a bad op amp cause this?

Bad parts are one of the last things you should expect, after you've exhausted everything else. Rather, since you have the same problem on two different vero builds, I'd sooner suspect that you've got a wrong value part somewhere, and you've used the same wrong value on both builds.

Get out the audio probe. Where does the distortion first appear? Is it distorted after the buffer, for instance? Does it appear at the input of any particular opamp, and then at the output (in which case, check the gain resistors).

Use your multimeter for continuity on the traces and parts -- not your eyes. Check against the schematic.

Tons of stuff will work there, but I'd suggest the 7530/7532 or the 9203 (it's in the list of CdS cells he has). Just buy several -- they're good for a lot of projects and have a really great switching range. They're also fast for a discrete LDR.

Okay. This will convert the Mangler 2014 to a positive supply ("negative ground") for NPN transistors.

Remove the charge pump. If you soldered it, I'm sorry but you'll either have to desolder, clip the legs, or get a set of PNP transistors.

Omit C7 and C8.

Jumper the pads for pins 8 and 5 where the charge pump would have gone. If you don't know which pins are which for the pads, search for the datasheet.

Reverse the orientation of the following:
The status LED (D2)
C2

You do not need to use the road rage (or any other polarity reversal) if you are using NPN transistors. The road rage is to convert the +9V of the power supply (from a typical adapter) to -9V for PNP transistors. You DO need to orient all your polarized devices so that the + side is facing the side with the highest voltage.

Let us know which Mangler PCB you're using and we can give further advice.

Lurkers are worth a lot of XP early in the game.


Wait ... nevermind.

Is the guitar wiring alright?

Yes, it's just this pedal.

How about that ye olde ungrounded AC plug in your jam space?  Does it hum when plugged in a grounded outlet?

Hm, good thought. I'll check tonight (my practice space has proper 3-prong outlets -- just the soldering iron and bench amp are on a 2-prong adapter), though I haven't had this problem with other gain circuits recently.

This happens once in a while, and I have no satisfactory explanation for it: You turn down the guitar pot and you get a bunch of hum. Put it at full and everything's fine and dandy.

In this case, it's the grease gun I just built, though I think I've had it happen in at least one pedal before. I know other people have posted about it, and I've never seen a good explanation.

My Grease Gun might not be too useful for troubleshooting (basically I've made a bunch of subs -- like all my coupling caps are 100nF now, so it's going to be hard to just say what the main problem is), but what might be useful is knowing what I've done to try to get rid of it:

1) Input series resistance? -- I see this floated as a solution sometimes. Nope.
2) Change bias resistors? -- No meaningful effect.
3) Cut the bass? -- To some extent this works (it's low frequency hum after all), but then I lose a bunch of distortion and signal!
4) Change the input device? -- No difference in my case with a BJT, MOSFET, or FET (with the positive bias removed) in Q1. Hum persists.
5) Buffer the input? -- I was certain this would do it -- after all, the problem only manifests when the guitar pot is turned down, so if the guitar pot is decoupled from the circuit, then it must ... Nope!
6) Move some wires around -- no change (so it's not RF, but I knew that)
7) Remove the pulldown? -- Nope.
Extra power filtering/100R on the voltage input? -- No change.

I am just mystified. I mean, I'll live with it, but I wish I knew what caused it. There's nothing about Q1 that I haven't built before without issue, and it's basically half a big muff, which despite overall thermal noise being an issue doesn't exhibit the volume pot issue I've got here.

So this is more of a general troubleshooting thread I guess.

That Prince one is hillarious. 

Thanks, Jon.  With all the experience out there, I'm hoping to find a solution that's pretty foolproof because I want to build one for a friend.  If it was just for me, some isolated ticking wouldn't be as big a deal.

Says Jon cryptically, "If you are willing to wait a while, there might be a different project to build that is less prone to ticking."

[Always check the datasheet.]

The vactrols you ordered will have a datasheet. The datasheet will tell you how the cathode or anode are indicated on the vactrol itself.

Always check the datasheet.

If you are still not sure, the LED in a vactrol is an LED. Your multimeter can tell you which side of a diode is which.

For the charge pump, I recommend getting the one that won't explode if it gets within an inch of 10V. To find out which one that is, check the datasheets (you want "maximum input voltage"). You also want to know that it can source enough current for your project.

Always check the datasheet.

I'm pretty sure Madbean's documentation tells you which ones are acceptable for use in this build. You can also use an LT1054, which is a very robust charge pump, if you remove pin 1 (or bend it away from the socket).

Today's lesson is:
Always check the datasheet when you have questions about a part.

Thanks guys for all the help. I thought I had this fixed but it has fizzed out again a few times. It seems to only happen when I put a pedal in front of it that juices it a bit. It happened with a compressor and just now with a Harmonic Energizer. I can go back in and rebias it and it will be fine until I put something in front of it again.

Any thoughts?

Remove it from the enclosure. See if it still happens on a test rig.

I won't pass any sort of judgment on "best" but ...

You should perhaps try the Hamlet by Midwayfair

Thanks for the plug, Ben!

The original, non-tap tempo version of the Hamlet only has three external pots (though you could make the "noise" trim external if you really wanted). I'm still pretty partial to that one, and it will be a little different from what you've already built -- brighter for one thing.

The PCBs are gone (I only do very limited runs of my PCBs), but there is a perfboard and etch layout in the build doc: https://docs.google.com/document/d/1P7uOYFRH6ZW5eGoquhAiMQMyUU76bod_gNKkiSlPNJM/edit. Haberdasher could probably etch you one.

CultureJam's/Grindcustoms De Profundis Delay also has a tone pot. That one gets VERY dark, but the repeats can also be super quiet at the absolute time limit of a PT2399.

*I don't have a good explanation for the electronic difference, just that they're hooked up a little differently and may affect the repeats differently.