Removing unwanted oscillation (Nobleman)

[ChrsGuit]

Hey guys... So, I recently built a Nobleman, and was surprised that I seem to like it best with the gain cranked...
I went back and bumped up the gain pot value to A500k value so I had a bit more range plus and minus...

Pedal sounds great, but once the tone and/or gain knob gets to a certain point, there is a background oscilation... not noticeable when playing but at idle, it's annoying...
Just curious if there is a simple way to filter out this oscilation... I really like the way the pedal sounds now, just want to get rid of this unwanted oscilation...

Also, if there is a way to slightly decrease the low-end (or boost treble) a little, that'd be great as well... pedal has a lot of low end, and I feel it sounds better with the tone knob set on the higher side.

 

[manfesto]

Not quite sure what to say about the oscillation since I've not experienced it myself before with this circuit, but as for decreasing the low-end, a common mod is to replace R7 (the resistor connected to the 2u2 cap) with a potentiometer to turn it into a bass control, or if you don't have room to add a pot, just socket R7 and try different values to change the cutoff frequency.

 

[swyse]

Make sure your wires, specifically input are well away from the board where they could pick up anything. Sometimes a buffer in front of a pedal can help with oscillation, but sometimes it's just the circuit or layout doesn't take the extra gain well.

 

[ChrsGuit]

Make sure your wires, specifically input are well away from the board where they could pick up anything. Sometimes a buffer in front of a pedal can help with oscillation, but sometimes it's just the circuit or layout doesn't take the extra gain well.

Make sure your wires, specifically input are well away from the board where they could pick up anything. Sometimes a buffer in front of a pedal can help with oscillation, but sometimes it's just the circuit or layout doesn't take the extra gain well.

I've tried this. I did take a piece of shielded guitar cable and hook one end of shielding to input ground, then ran the wire from input to switch... It helped SLIGHTLY, but not completely. I've seen some suggest a very small value resistor from the input of the op amp signal input to the ground if the op amp to bleed off any oscilation (If I wrote that wrong, my apologies... that's just from memory and I'd confirm before trying...

My understanding is the oscilation is literally the "excess" signal introduced bleeding back through the circuit and causing the issue

 

[Lorok]

I also have this oscillation issue with the volume and gain pots close to max (when there's no or low signal coming from the guitar). Plus I hear this oscillation (albeit a lot quieter) when playing dissonant bendy intervals at lower volume and gain levels as well...

I wonder if anyone has any tips on how to troubleshoot this.

 

[Lorok]

Oh, I tried adding an additional 47uf between GND and Vref as mentioned by Robert in this post and indeed it seems to fix the oscillation at max vol and gain for me.

Edit: but why do some builds have this issue and others don't? What other variables are at play?

 

[Lorok]

So for anybody else that will be looking for solutions to a motorboating Nobleman...

• Madbeanpedals Laureate (ODR-1 clone) build docs have this to say:

Something interesting I learned on this project: On most circuits, you can be quite flexible with power decoupling on virtual ground (VB) because of the well regulated outputs we have on power supplies these days. I generally use a 10uF cap for decoupling out of habit. Turns out in some circumstances this can be a big problem and it was with the first Laureate prototype I built. With my standard 10uF cap I experienced really bad motorboating at higher gain settings. After scratching my head for an hour trying to debug the issue I found it was a result of using too small a value on virtual ground. Once I reverted to what the ODR-1 uses (a 100uF and 47uF in parallel and placing each relatively close to an IC) I was able to eliminate the problem completely. So, as you work on your own high gain circuits keep that feather in your cap in case you ever run into a similar issue.

• AionFx Andromeda (ODR-1 clone) Legacy version build docs about adding an addition 47uF cap to the Vref line:

I added C24 to counteract some low-frequency oscillations at high drive settings. 22uF is probably OK here.

In the current version of Andromeda though, this additional cap is missing. Perhaps their new layout is optimized to avoid signal coupling .

tldr: I ended up adding a 100uF cap to the VRef line, which fixed my issue.