I've just finished building my Pedalshield UNO but I'm not getting a good output just mostly noise. I've read the previous troubleshooting notes and have followed the steps. The sine wave output is good, so the output stage works. With the clean sketch loaded, I still get a ton of noise. I see a problem on the board but don't understand what's causing it. I have a voltage drop across R3 of about 1 volt. I have 2.5 on one side and 1.5 on the other. I suspected a shorted capacitor but can't find any problem. I've also checked for shorts on the solder joints and have touched up everything. I removed the op amp to see if it's shorted, but that doesn't seem to be the problem, Since checking for 2.5 volts on both sides of r3 was mentioned in the troubleshooting, it seems like it's a problem that has been seen before. I've checked all of the resistors and they are all in the right place and read the correct values. I'd appreciate any advice.
Some pics of your board could help and how things are setup...Noise could be a number of things. Could be how you are powering the uno, either through the computer usb or a dedicated power pack. some cause way more noise than others.. You could check the RV1 trimmer and set it in the middle..it could be set too low. I too am dealing with this on my prototype shield i did..Sometimes another set of eyes on what you have could help...In my case mine is due to a crappy output cable between shield and amp. I'm guessing you have the actual pedalshield pcb.
Thanks for the reply. I've tried powering it with the USB, an AC adapter and a 9 volt battery all with the same result. I'm using the official shield kit. I have the VR set in the middle and have adjusted it with no result. No matter which effect I load I get the same result, you can hear the guitar , but there's a lot of hiss and crackle like I have a bad cable, but when I'm in bypass everything is good, so I don't think the cable is the problem. I'll try to post some pics later.
Try to adjust the VR1 potentiometer, if the gain is too low could be that the guitar signal presented to the operational amplifier is too low and the noise will be audioble.
Hi, I've tried to adjust VR1 several times. I'm attaching some pics of my build, but I've been over it with a magnifying glass and I've checked all of the connections. Still maybe someone will see something I've missed. As I said in my first post I drop about a volt across R3. is that normal?
As I said in my first post I drop about a volt across R3. is that normal?
No, this is not normal, in my system I read 2.674 in one side and 2.676 in the other side of R3, the voltage drop should be minimum.
What happens if you unplug the TL972 op-amp and measure again? (do the connection/disconnection process with the pedal unpowered)
With the op amp unplugged the voltage drops from 1.5 down to 1.2 volts on the op amp side of r3. I suspected a shorted cap was giving a path to ground causing a voltage drop but I desoldered a pin of the two caps in the circuit with R3 and the problem remains. It's really strange. I get the right readings between VCC and Gnd based on the schematic but current must be flowing through R3 to drop voltage across it.
Thats interesting... It would be ideal to find where that current is going to.
With the IC disconnected from the socket, it should be no current flowing through R3.
Could you check with a multimeter if there is any short around R3 (whith th op amp not placed), maybe a short betweens pins 5 and 6? maybe double check R3 value? with the IC disconnected, which is the resistance between pin 5 and GND?