I'm new to audio probing, but I'm learning. If anyone can give me some tips that would be awesome, any knowledge and experience is welcome.
Just wondering, sometimes the signal is weaker on one side of a resistor to another, is that just due to the resistance value and not a defect?
Sometimes I've found signal to be quieter on the cathode side of a diode, depending on the diode, this is correct and due to the clipping right?
Also, should I generally always be able to get signal on the first two pins of a pot? If I don't does that mean the pot is bad or there is no signal getting to it?
Once again, any wisdom/knowledge/experience appreciated
Successful audio probing requires some understanding of circuits. Not all components should have signal and it is appropriate if sometimes the signal you hear at some nodes is very weak. To start, focus on active components: transistors and opamps. You can make troubleshooting threads for each of the circuit you are debugging and I’m sure you’ll find people who will guide you and recommend where to probe and how to interpret what you hear. Good luck!
While your specific questions are valid, we need to know more information about the circuit(s) and have references to the schematic. Whether a particular component has signal strength on one side as opposed to the other does not provide enough reference to answer your questions. Where in the circuit a particular component sits determines how it needs to be probed.
Successful audio probing requires an understanding of basic electronics and schematic comprehension. And even with those skills, the key to successful audio probing is being able to examine a schematic and identify the signal path. With the ability to identify the signal path, one can then use an audio probe to test for the audio signal along that path.
Without an awareness of what level of electronics and schematic reading you're at, (and with all due respect and bearing no intent of condescension), if you're skilled in basic electronics and/or schematic comprehension, it will come down to exploring the schematic along side the circuit being probed and sorting out. For most, the primary key is to be able to cross-reference (map out) the schematic to the component locations within the circuit. And vice-versa.
Then there are the various audio-probes to explore. Some are extremely simple - just a piece of wire attached to one end of capacitor.
(eg: Here's what I personally use. A long-ish breadboard wire, a 0.1µF @250V cap and an alligator clip.)
I simply attach the alligator clip to the output of the circuit; (note that the circuit is set up for full testing and its output is also connected to an amp of some sort); then with an audio signal being input to the circuit, I will place the tip of the probe on the signal path points starting with the input section and working my way toward the output. (This is where schematic reading and electronics foundations will help a lot.) One could also start probing from the end (output) of the circuit and work their way towards the input.
Audio probes can also be quite elaborate to simplify connection points and circuit I/O & path access. They make all sorts of audio probes for all kinds of circuits. (I prefer to keep it simple.) There are also tons of web pages that show how to DIY your own simple or more complex audio probe. (I just searched "audio probe DIY" and got many good results.
As @giovanni points out, starting a troubleshooting thread is also a good place to start. And with that done, it's also good to know how far along you are with schematics and electronics, how much assistance is needed, a reference to the schematic of the circuit, and some good clear photos of the circuit and its connections. Then the group may be better able to facilitate your troubleshooting assistance.
So, where are you at (if you lease) and what is the circuit you're working on?
I agree with Giovanni. Always check the active components. Plus voltages. Op Amps are easy. I usually make sure of the original signal onto the board and then probe the pots. In my experience bad soldering is a usually cause or even forgetting to solder part of component.
Sometimes a diode oriented in the wrong direction. As last resorts a resolder the entire board and then check the values of parts.
I met a guy who claims he was audio probed and the aliens were rough on him.
Kidding aside, I use a mobile phone, a four conductor 1/8" jack which converts to RCA with 1/4" phone plug, an app called 'Hz Frequency Generator' and create a 1Khz sine wave with the volume on the phone about 3/4's up. Then I use a Tectronics 454 oscilloscope to view the sine wave from the input jack of the pedal or amp, through the signal chain or the suspected failure area typically using a schematic.
There are other methods, but this has been the most reliable for me.
Thanks for the response guys, much appreciated.
I can read schematics and have a basic understanding of what the circuits are doing, but I wouldn't know exactly what to change in a circuit if I wanted to modify the sound if I didnt like it. Thats about my level but I am trying to learn more and improve.
I am trouble shooting 3 pedals at the moment and not getting very far with the spare time that i have. The questions were specific to one of the pedals I'm troubleshooting, and I will start a thread for it eventually, was just pushing myself to see how far i can go without help but I'm new to audio probes. I have made one and am using it when I can.
The pedal is a Cetus preamp and it has really low output but sounds like it should. Just really quiet. The diode question relates to a 2.7v clipping diode just wanted to make sure that the output is meant to drop on the other side of it which makes sense to me as it is pretty significant clip. Transistors and op amps have signal. The potentiometer question is the volume pot B1M, I can trace the signal to the resistor before it then signal stops, I've never been able to get signal on any of the volume pot lugs. I replaced the resistor before it (R10) and it changed nothing. All the other pots have signal when probed.
I will start a thread for it eventually just wanted to see how far I could get myself. The other two pedals I'm troubleshooting have got me stumped, one only works for 30 seconds or so when you touch the pcb with your finger, and the other is just a high pitched squeal!
All PCB's have been component checked and re-flowed.
If you have any more tips and tricks, I'm keen for all the knowledge you have. Everyone loves a good probing.
