1000 Hurts: Stomptown Harmonic Percolator Clone Build (from hell)

[eightysixbret]

A year in the making. This project somehow survived two moves, three trips to Colorado, a breakup, a reconciliation, seasonal affective disorder, closing a business, three different VU buffer circuits, a bad transistor, and various other obstacles that had to be overcome to finally wrap it up. The worst of those obstacles had to do with the finish, which turned out to be a nightmare, and then there was that one time nothing on it was working. Luckily, Leevibe swooped in like the hero he is and fixed a bunch of my rookie mistakes. You see, this was to be my first real build, but it seems I bit off a bit more than I could solder, so to speak. And so it sat on my bench for months at a time, mocking me every time I walked past it, guts all exposed and strewn about; lacquer fumes invading my sinuses like an unwelcome house guest.

So yeah, this is a clone of the Interfax Harmonic Percolator, using a Stomptown PCB. Since this pedal is Steve Albini's go-to distortion mayhem device, I decided to name it after a Shellac album, and to give it a design treatment that brings to mind an obscure military weapon of torture that was recently unearthed. Honestly, much of what looks like "relicing" is actually a crappy finish that dents, cracks, and clouds up when a mere mosquito flies by it. So I'm going to run with it and probably make the distressed effect look more intentional and natural. And then there was the VU meter. Something that seemed like it would be such an easy little fun visual gimmick turned out the be a complete pain in my ass. After trying a VU meter buffer kit from DIY Tubes that stopped working at some point (that I probably fried in one of my failed tests), I finally slapped on some pants and read up on opamp buffer circuits and rolled my own very simple circuit. Does it work? Yeah, it moves the needle when the pedal is engaged and played through, but not a ton. Close enough for government work, says I, and fitting of the theme. So, for now, I'm calling this bastard done. It's going on my pedalboard. Today.

[Bret608]

That is nuts! Nice job. It's got that Shellac vibe for sure. A Percolator was my first build, incidentally. I've built a second using a Stomptown board. Both the "stock" and Albini specs are really cool.

[midwayfair]

What's the second footswitch?

Do you want some advice with the vu meter in case you decide to go back in? You just need a couple resistors to add some gain to it. I'm not sure how you have it hooked up, but the perc will spit out more than 1V without breaking a sweat, which ought to be enough make the meter jump to -3 at least. I'm squinting at your buffer layout and I don't see any resistors to create a bias voltage, so it's possible the op amp isn't actually working.

[chuckbuick]

That's a great build, man.  Props to you for sticking with it through the bad times, too.

[eightysixbret]

What's the second footswitch?

Do you want some advice with the vu meter in case you decide to go back in? You just need a couple resistors to add some gain to it. I'm not sure how you have it hooked up, but the perc will spit out more than 1V without breaking a sweat, which ought to be enough make the meter jump to -3 at least. I'm squinting at your buffer layout and I don't see any resistors to create a bias voltage, so it's possible the op amp isn't actually working.

The second footswitch is there to flip between the two different gain methods. It's a minor difference, but the "stun" setting is less overdriven and muddier than the "kill" setting.

Absolutely, I totally appreciate the advice! So in the previous board I'd wired up for the buffer, I had those resistors, but that board tanked between the breadboard and the perfboard. In hindsight, I think I fried the opamp at some point. So I saw a more simplified circuit without the resistors and that is basically what this is, with the exception of a 47uf output cap instead of 10uf (I was getting bigger needle spikes with the 47uf when running a sweep tone through it). As for output values, I believe it's currently outputting around 1.4v after the cap. The needle seems to hang between the -10 and -7 marks when I'm playing, with the occasional spike above that. So much of this stuff is still pretty abstract to me, so any guidance is much appreciated. Thanks!

[Martan]

I think its awesome! Love the look and everything. And from a disengaged outsider perspective with no skin in the game, you should definitely try what Midway suggests to fix the VU meter

[Lubdar]

Heh love the thread title! the VU meter is a nice touch

[Leevibe]

So good to see this build report, Bret! I'm proud of you for hanging in there. It looks really sweet man.

[midwayfair]

So I saw a more simplified circuit without the resistors and that is basically what this is

The thing is -- that schematic you found without those resistors almost certainly uses ground as the bias voltage, and positive and negative DC supply voltages for the positive and negative pins. There are three voltages involved in an op amp schematic without extra resistors. In a pedal that runs on +9V DC like this one, you only have two voltages: ground and +9V.

What I'm seeing on the perf is that you take signal from the pedal, run it through a yellow (1uF?) cap to pin 5 of the op amp, put a red jumper between pins 6 and 7, then take the output from pin 7 through a big big electrolytic capacitor to the Vu meter, and pin 5 is grounded, while pin 8 is connected to the +9V.

Your op amp isn't actually op amping. It's also probably doing funky things to the signal it's connected to in this situation.

The fix really is just three resistors, a 10K from the power supply, a 10K from ground, and a 470K to the input, and then all three meet in the middle.

Adding signal gain to it would require more parts.

[stringsthings]

Very nice !  It's a got a cool army type vibe going.  Love the VU meter !

[lincolnic]

This looks great, glad you got it working!

I also think you should take Jon's advice, get that VU meter rocking, and then take a video for us. 

[bcalla]

The nice thing about a cool build is that others looking at it have no idea what you went through to get it to where it is.  And eventually, even your own pain will be a distant memory...

Great build!

[matmosphere]

That looks great! I really like the knobs, they fit the style perfectly.

Looks like Stomptown doesn't sell that board anymore. Anybody know where to get a good board for a percolator.

[Willybomb]

Man, I am so going to build a pedal with a VU or LED meter in it one day.

[Stomptown]

Man, I love the concept regardless of all the issues you had along the way!  Very cool aesthetic Brett!