December 11, 2019 at 1:17 am #8535
I have my 4 track fuzz completed and while it makes all the sounds in the demo videos online there is a squealing that is always there. Could this be a problem with the TL072CP I have in it?
JeffDecember 11, 2019 at 7:54 am #8536
It could be several things causing the op amp to oscillate Jeff what are your the voltages on the TL072 pins
Upload some nice in focus images of both sides of the pcbDecember 12, 2019 at 1:22 pm #8549
I sent pics via pm because every time I try to upload or link pics my post disappears, not sure what I did wrong.December 12, 2019 at 2:41 pm #8552BarryKeymaster
Still need voltages.
You can only upload 1 pic at a time.
You cannot link pics without it being an absolute direct link. In other words most photo hosts do not provide direct links for commercial reasons. If you are using a VPN while in the forum not much will work. My site is setup to block all VPN to prevent brute force hammering my site for passwords.
Here is a direct link from my site:
Here is an uploaded picture.December 12, 2019 at 5:04 pm #8555
I knew I was doing something wrong.December 12, 2019 at 5:07 pm #8556
The horrendous soldering of GND (PCB) and O (3pdt) have been fixed since I took the photos. Voltages were 14.2 pin1 and 13.9 pin7December 13, 2019 at 4:44 pm #8570
What are the voltages on all the TL072 pins Jeff with it in and out of it’s socket
List them like this obviously indicating which is with it in the socket and with it out
And just in case you don’t know pin on the top left at the dot / notch is pin 1
I’ve checked all of your component values and orientation which all look correct, can’t check pot values so I’d double check the correct values are in the correct place
Once you’ve posted voltages for the TL072 it should give us an indication of whether it is the cause of the oscillation i.e incorrect voltages causing mis-biasing etc
If you can post a picture of the rear of the pcb alsoDecember 13, 2019 at 5:45 pm #8571
8. .1 *jumps to 5.7 back to .1 led turns offDecember 13, 2019 at 7:16 pm #8572
Those voltages look way off Jeff
You say you get the sounds in the demo and squealing is the main problem but with the voltages given it wouldn’t work properly pin 4 should be ground 0v pin 8 power supply around 9v the other pins should all be around 4.5v
Are your readings 0.5v pin 1 and 0.1v etc aside from pin 8 which jumps from 5.7 back to 0.1v?
Did you take the readings the normal way by putting your black probe on a circuit ground point and touching your pins with the red probe with your meter set to 20v dc
I’m just confused that it worked aside from the squealing with the voltages you’ve given and suspect your meter may be set to 20v acDecember 13, 2019 at 7:47 pm #8573
I had it setup wrong! oops
8. 10.52vDecember 13, 2019 at 9:43 pm #8574
Try using an adaptor that puts out 9v or a 9v battery to power it, 1.5v over voltage may be enough to affect the TL072 biasing and cause it to oscillate it shouldn’t but that could be the cause with 10.52v going in, good news is you know your voltage dividers R10, 11, 12 and 13 for VA and VB are doing what they’re supposed to do halfing the supply with your TL072 inputs and outputs being 5 odd volts
Use your finger to tap the TL072 to see if it affects it
Also take the readings with the TL072 out of the socketDecember 13, 2019 at 10:28 pm #8575
Used a universal adapter with switchable voltage, started at 9v and dropped it to 7.5v and 6v it dropped the pitch of the squealing but it never went away.
Tapping with finger didn’t affect the sound.
Readings with TL072 out of socket:
1. .01 v
8. 10.41vDecember 14, 2019 at 10:10 am #8582CybercowModerator
I can’t help but wonder if those un-insulated pot bodies could be touching the solder-side of the PCB and creating issues.December 14, 2019 at 10:38 am #8583
The next thing I would personally do Jeff is try to track down where it starts
Op amps will go into oscillation if they are being fed incorrect voltages as I said a few things could cause it dry solder joints, incorrect values etc I’m not 100% a volt over VA, VB 4.5v would cause it that is why I suggested trying a battery to rule that out or a regulated 9v power supply
I would first of all use an audio probe and check audio going in at IC1A pin 3 where I wouldn’t think you’d get it then check pin 1 output where you may get it that at least will give you the area to look at
Some of your solder joints do look suspect
Where did you get the TL072 and what wattage is your soldering iron I also note that R2 and a few of your 10K resistors are 1/2 or 1 watt size R2 is in the IC1A feedback loop so it could be with its thicker legs it’s not making good contact with the pcbDecember 14, 2019 at 7:29 pm #8584
I get audio off of both pins with the probe.
Should I swap R2 out?
TL072 was from Mammoth (I know they are closed down at least temporarily) I do not have a spare or any other compatible op amp on hand.
I use a Weller 7760 handle with a 45 watt iron
I reflowed many joints but nothing changed, but my soldering is not the best.
I don’t have a 9 volt snap to try on the pedal so I only have my various power supplies, the oscillation is present with all.
I have tape on the back of the pots but it is possible that it’s ineffective.
I have no doubts the problem lies with my abilities or a faulty component and lay none of the blame on you guys. I built a Fuzzy Bee at the same time and it works perfectly.December 14, 2019 at 9:09 pm #8585
No don’t swap anything out the idea is to use your audio probe to see where the squealing starts
You should get clean signal with no squealing into IC1A pin 3 if you then get squealing out at pin 1 and in at pin 2 that would indicate your problem lying in the feedback loop components between pin 1 and 2 as i say the idea is to try and locate where it starts
45 watt is a little to hot for pcb work I wouldn’t go more than 30 watt
Your pedal works so you’ve built it correctly and it’s just a case of finding where or what is causing the squeal is it present throughout the range of the gain pot and does any pot alter it
Regarding the power supply I always use a filtered, regulated supply and never the non regulated cheaper option especially with high gain circuits using a battery means pure DC so no unwanted noise from AC ripple as I’ve said im not sure if 1.5v over bias voltage is enough to make an op amp oscillate
Just for future reference I use these to test with batteries to rule out the supply being the problemDecember 14, 2019 at 9:51 pm #8586
I tried the probe again with my guitar and my chaos nand that I built. Pin 3 is pretty clean with a hint of squeal and 2 has quite a bit of squeal. I get nothing off pin 1 not sure how I did earlier.
With the effect switched off and no input there is still a faint squealing if I crank up my amplifier.
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