Troubleshooting a Canned Yam

[sam6025]

Long time reader, first time poster...

Alright, I have built quite a few pedals at this point and have never had one that didn't work, so I'm hoping one of you might be able to see the issue. The only thing I've done differently than most builds is change up the pots due to not being able to find an a25k 16mm pot. I also used an a100k dual gang pot instead of the a50k, but looking at the initial build that Rullywow posted on here, he used an a100k dual gang, so I figured that wasn't an issue. I've used different pots in the past and had different responses than I wanted (bunched up signals, etc), but it's never just not worked. However, if the answer I get is "Look, dumbass, use the right pots and it will work!" I'll actually be thrilled. I'm just putting off removing these until I get some input. I do have an a25k pot, but it's a 9mm, so I've been hesitant to change it. I also have an a50k dual gang that isn't PC mount, so I can use wires if need be.

I've checked the resistors and caps about 3 times to make sure they're all right and they are. I've never had a board with the backside 9V and G lugs, but I'm guessing it is to make it easier to put to direct power if you're not using a PCB on the 3PDT switch. I have tested it with just the front side power, just the backside and both connected. Nothing happens either way.

Thanks so much for any assistance.

Here are the pics:

[Jebus]

Hey!

So whats wrong with it? No signal at all?  Audioprobe is usually the easiest way to figure out where the signal is lost.

Also, post voltages from the IC.

[sam6025]

Thanks for the reply...it's just dead when I engage it. I'd never used an audioprobe before, so I'll put one together when I get home from work this evening. And I will post voltages when I get home. I've been somewhat paranoid about the socket since this is the first time I've used a socket for an IC, but everyone uses them so it's probably not that.

Thanks for the audioprobe tip. I've done guitar modifications and pickup building for years, but I'm just getting into pedals in the past few months. So there's a lot of troubleshooting I don't know. Many thanks.

[sam6025]

I haven't done the audioprobe yet, but the IC voltages are:

1. 4.82v
2. 4.82v
3. 4.54v
4. 3.7v
5. 4.53v
6. 24.5v start and over 30 seconds kept dropping to 18.3. I'd imagine it would keep dropping, I just figured 30 seconds was enough time.
7. It ran up to 18.3v and started decending the same way lug 6 did.
8. 8.74v

I'm guessing 6 and 7 aren't supposed to do that.

[sam6025]

I followed the clues and popped in a new IC. It works now. The Q function doesn't really change anything at all. I'm going to switch out the a50k pot to a b100k pot. Maybe that will help? Thanks for the leads, I never thought of testing the voltage through the circuitry.

[jimilee]

I'd say putting in the 100 will make a noticeable difference for sure. I've been meaning to try that preamp. I'd love to hear your thoughts after you get it running.


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[Betty Wont]

I'd say putting in the 100 will make a noticeable difference for sure. I've been meaning to try that preamp. I'd love to hear your thoughts after you get it running.


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Its a good one. My favorite pre for slap like old les claypool and stanley clarke.

[sam6025]

It's sounding pretty cool. I'm not hearing a lot of change on the Q, even after changing out the pots, but I've been playing pretty low volume testing it through a crappy guitar amp. The switch definitely thins it out or adds a big boost to the low end. I'll play with it a lot more tomorrow and report back. Right now, I'm happy with the functionality it gives.

[Willybomb]

I've been meaning to try that preamp. I'd love to hear your thoughts after you get it running.

Build one Jimi. I built one on vero a couple of years ago, great stuff.

[jimilee]

Oh yeah! Does tag board has a layout?


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[Willybomb]

No, but Paulinthelab does - that's the one I built.

[sam6025]

After letting it sit as partially functional over the weekend, I looked through the schematic and checked one of the electrolytic caps that would effect the "FREQ" setting. Sure enough, the lead was broken inside the cap, probably from changing out the pot. I put a new one in and it sounds great. The FREQ does a great sweep from pronounced high end to house rattling low-end. The Q fine tunes a lot of things. I went from being bummed out about the limited EQ possibilities to being really impressed. We're using it to level things out and boost the low end between an electric bass and a double bass with the same amp. It definitely helps even everything out.

[jimilee]

Great to hear, I'm pretty excited to build one.


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