I just got finished populating a tonepad version of the cp9 a buddy made for me. Once I pluged it up using a bread board I have no from the guitar. When I turn the pots I can here audia le change just no guitar signal. The whole board has voltage. I'm guessing this is a prob in the input area. Agree?
At this point I'd be using an audio probe. Work the usual debugging steps.
Check your parts. (and again)
Check your wiring.
Check your voltages.
Start Audio probing at either the front or the back. (use the schem)
At that point, you should get a clear picture of where the signal stops. It could be as simple as a bad wire or something silly like that. Could also be much more complicated, but you see what I mean.
Jacob
ok. I probed around the other night and the signal stoped a couple components in. I have a sneakin suspicion that mister Q1 has a prob. This will be like the 3rd tranny gone bad. Is this normal? I havnt yet figured out how to test a tranny. (havent really tried yet) havnt wired yet.
lol jacob you need to set me up a hotline. You've helped me with most of my builds. Thanks man.i know I ask a million questions. That's just how I am. I like to know everything about what I'm doing or it doesn't feel right. This pedal building deal has become such an obsession. I really don't think I'll ever quit.
Depends. Are you soldering them in or socketing?
If signal is stopping at a transistor, there could be a number of problems:
1. It's backwards or the pins need to be rearranged.
2. It's not getting power properly.
3. It's not soldered in correctly.
4. It's been fried.
So really, until you've verified 1-3 is not the problem, don't assume it's bad. The most common way to fry a transistor is to apply too much heat. This is harder than most people think it is - they are hardy little devices. However, it is possible.
Jacob
*edit* No problem. There's two things I'm good at with pedal building. Debugging and soldering PCBs. I'm not a super star, I just build more than the average and have a broader base of debugging than the average builder. Lots of guys understand things waaay better than me, like Scruffie with BBD circuits and Brian with general electronics knowledge. I know what I am good at though - posting too much on forums!
Jacob
well.. I have probed and probed all night and changed several parts and I'm really struggling on getting ANY where with this one. I can't find and voltage info on thos circuit.. Right after the input there's a 1m res and 47n cap. The res goes to ground and the cap goes on to a 10k res into Q1. I can only get a signal on the first lead of the 47n cap. I have replaced this cap twice.. The third one still nothing. I also removed 10k and tested. Q1 has voltage. One leg at like 8v (i even replaced this).. I'm wasting parts here and getting nowhere. I'm gonna have to figure away to get pics.
K. If you are getting signal at the junction of that input resistor and cap, but after the cap there's nothing, the first thing I think of is that you have something going to ground at that point. The only reason not to have signal between the 47nF cap and the 10K resistor is that it's bridged to ground somehow. Or your 47nF caps are all faulty, which is very, very unlikely.
I can imagine how frustrating this would be. I had a similar pcb that drove me bananas until I learned that the PCB itself was a failure. Since I had 3 copies from the run at dorkbot I made a 2nd. It worked fine first try, but that first one somehow was leaking the output to ground. Had NO idea why or how, it was impossible. I'm not saying that's the problem, but rather I know how frustrating it can be.
Keep at it until you can stand it no longer, then put it down till next week.
Jacob
it's almost like everyone of the caps aren't letting the signal through. On one side when I probe I can hear it. On the other side I got nothing.... And as far as I can see it's not grounded. I mean.. It runs right next to a ground trace but the aren't touching. Pretty much those caps are bad or it's some how touching the ground. Wonder it needs a jumper to the next resister. Or if I disconnect the leg the I can't hear and tie it directly to the next resister?? Jacob.. That would work man.. You think?
Hey Grant,
Before you go farther, tell me how you know that the leg of that 47nF is not connected to ground? Have you checked using a continuity test with a DMM? When you use your audio probe, if you're touching an area that connects to ground you won't get any signal. The proximity of those traces to the ground trace make me guess that you have a hairline, almost invisible connection to ground.
Take a look at the schem. You can trace the signal along from the input, and essentially, signal HAS to go through that joint. You can do that any number of ways. You can tie the leg of that cap to the resistor without using the pads of the PCB, or use the PCB, or use a jumper, or whatever.
Jacob
ok.. I guess I can't tell you for sure. But it very well could be a tiny hairline. I don't know how to check for continuity. Is the the setting w the schem symbol of a diode? But seriously that is exactly hows it's behaving I just didn't think that through. When I get in tonight it's back to the work bench. And I'll get back to ya
ok jacob. I got very useful info. I figured out how to check continuity or what ever it called. So.. When I touch to one leg of the cap and the other there is NO beep. When I check the leg of the cap and the 1m it does beep. When I touch the bad leg of the cap to the 10k it does beep. And when I touch both ends of the 10k res I get NO beep! This means somewhere in the connection from 0.47cap and the 10k it is grounded right?? Bc I think I touched that connection and with other probe I touched ground and.... It beeped lol. tso if I attach those to legs I will atleast eliminat THAT prob correct?
Ah, now we're getting somewhere.
You need to recheck this - do you get a beep if you touch connection between that 47nF and 10K resistor and Ground? If so, that means it's grounded, and that's the source of the problem.
There are a couple things you can do. If you can use a magnifying glass and a light you can sometimes find them and then use a small razor blade or an exacto knife and cut the connection. Some people skip right to using said knife to cut any connection by cutting along the area between that joint and the ground plane/ground joints nearby. In some cases, you can simply use your soldering iron, reflow he joints and break the connection that way.
If you have a Macro function on a camera you can take a shot and I can take a look, however it's usually something only you can diagnose.
If for some reason none of the above works, yes you can make the connection manually by doing a teepee of sorts. However, I advise against that unless you can't avoid it.
Progress is good right?
Jacob
Ok! We did it! Before I read you're post I manually connected the cap and res BC it like crazy when attached to ground. Ididnt r.ealize I could use acto. It works and sounds pretty damn good sorry for the poor Grammer.im on my wives phone with this auto text.thanks man.success is great
one more thing.. The way this board was made is it only ises half of the lm13600. On the other side of the chip are rows of soldering pads I'm guessing are for mods using the second amp of the chip maybe? What are some mods for this thing? Tone? Blend? Grit? I wish I could add grit like the pigtronix philosophers tone.
Great to hear. I think you're starting to get a hang for the steps in debugging now Grant. Work them, and find the ultimate root of your problem! Defeat them, and you'll be teaching others soon.
As for the mods, great idea. I took a quick look, and I think a neat mod would be to run a parallel gain circuit, like some distortion. You can actually design a circuit around it, and since power and ground are already there you can cut down on the extra parts and just go for one gain stage with some clipping! Easy enough I think. Read up on how the tubescreamer works and canablize the gain stage and output section...
Jacob
ok. Thanks for the comiment. Very encouraging. I have NO outlet here for help or instructions. I have tought myself how to do this with pretty much the help from... Hmm mostly you lol! I just ordered a fancy enclousure from pedalenclosures.com for this one bc I love it so much. Now back to the issue. I took a look at the gainstage and it seems pretty simple. Heres my issue. If I add that to the other side of the op amp and plug it into the out put, what happens if I turn the gain all the way down. Will it go back to the clean effect or will the volume go all the way down? I've never messed w anything like this. Also, I don't want it to be to gainy. Just gritty. Would the diodes determine this? Could I use mosfet or jfets to clip w one GE diode? I hope I can do it w jfets bc the only mosfets I have are the irf510. Freakin huge. Could mount them on enclosure and wire? That'd be pretty bad ass. Anywho. Let me hear your thoughts bc I'm liking this idea. I just want to make sure I can bypass the gain. Maybe put on switch?
I just placed an order for a couple 500kb pots, mosfet bs170 and a couple GE diodes. It's said and done. So I'm gonna try to bread b it later
dude, I'm gonna need some help with this. This is hurting my brain. I can't come up with how I can lay this out using what I have.. At what point in the circuit should go into the gain stage. Should it go out directly to the output pot? It looks like I have just enough room to do somthing w no room for error.