Hi all. I'm building a knight of tone PCB. So far I only put together one side to see how I like it. Overdrive works. Boost works. Distortion starts making a low oscillating type noise when gain hits about 3oclock. I had bat46's in the clipping and changed it to 1n41448 and now it makes the noise around 4oclock. What gives?
I tried removing the charge pump but it does the same thing at 9v. I was looking forward to trying the high gain mod but that doesn't seem like it work at all with this issue. What do I not understand about this op amp or is it the diodes? I checked resistors/caps and I have the right values everywhere. I also replaced the op amp and tried an tl072 as well. Same issue everytime.
Check out the build.doc and pics below.
https://pcbguitarmania.com/wp-content/uploads/2022/05/Duke-of-Tone-Building-Docs.pdf
(https://i.postimg.cc/dhYz4kbd/IMG-20220926-163658.jpg) (https://postimg.cc/dhYz4kbd)
(https://i.postimg.cc/WhMyFpd4/IMG-20220926-163643.jpg) (https://postimg.cc/WhMyFpd4)
I had a similar problem in a different circuit that has two clip-to-ground diodes, one of which was not connected and that was causing a low oscillation at high Gain knob settings. Verify that both your clip-to-ground distortion diodes have good continuity to the signal path on one end, and to Vb (1/2 of the supply voltage) on the other end. And verify that they're both installed with the correct polarity. Both of them facing one way will cause this as well.
<edit> also maybe some insulation between the back of the pots and the solder side of the PCB? A piece of electrical tape or some thin cardboard would do it, to prevent them touching and shorting something.
Checked all of that and it's all good. Still low freq oscillation. Why do bad things happen to good overdrives?
Does anything change if you move the wiring around while it's oscillating?
Is it being powered by a battery or 9v supply? If supply, is it a known 'good' wal wart that has no problems w/other pedals?
Verify clipping diodes MODE _A and MODE_B are wired correctly on respective switch..
By activating both clipping configurations simultaneously, you might result into annoying effects..
do you have any wire connected to ground for the in and out, or are you relying on the power supply wire?
The wiring at the moment is only the 9v and jack.in and out. This is to plug it in to my breadboard/test box that I always use. The wall wart is also reliable.
There is no wiring for the switch which is mounted to the PCB. Switch is also tested and good.
What's weird is I can dime the gain and it works if I play super soft. The second I push too much signal is when it oscillates.
Quote from: duck_arse on September 27, 2022, 11:05:16 AM
do you have any wire connected to ground for the in and out, or are you relying on the power supply wire?
The grounds are all tied together
Quote from: SprinkleSpraycan on September 27, 2022, 12:12:43 PM
What's weird is I can dime the gain and it works if I play super soft. The second I push too much signal is when it oscillates.
A wrong value resistor (e.g. 2k7 instead of 27k for R5 or 100k instead of 10k for R3) could easily result into the above issue.. :icon_wink:
I'd short IC1_A pins 1 & 2 to isolate the problem between stages..