Mach 1 + Southern Belle Combo Noise When Stacked

[Lukasz]

Hello,

Wanted to try those pedals for some time, I finally decided to build them as combo (First Stage: Mach 1 + Second Stage: Southern Belle).
As result each stage works as expected running alone, issues start when i try to run them both. After setting the Gain above 50-60% on any of them, when stacked
i am getting high pitched noise.

I did some research online and i figure out that i am not the first one to face this issue.
Mach 1 and Southern Belle are very similar according to schematics.

Do you have any suggestions according to circuit that could be implemented to reduce this noise? Some filtering?
I was thinking about replacing the 100pF Caps to i.e. 220/330pF.

Schematics
Link: https://docs.pedalpcb.com/project/PedalPCB-Mach1.pdf
Link: https://docs.pedalpcb.com/project/PedalPCB-SouthernBelle.pdf


Any suggestions welcome. Thanks.

 

[jwin615]

By "high pitched noise" do you mean hiss, oscilation, or...?
Does it change with the guitar volume pot?

 

[music6000]

Are your Input & output jack leads going around the outer edge of the PCB?
You could try increasing C100- 22uf to 100uf on both.

 

[Lukasz]

By "high pitched noise" do you mean hiss, oscilation, or...?
Does it change with the guitar volume pot?

It is more like whistle / oscillation. It is making it even with guitar unplugged.
I added 470pf parallel to 100pF in opamp loop and it is better, with 1nF cap added noise is almost gone, but the sound is also darker.
Maybe it would be beneficial to add some caps also in second opamp?

 

[Chuck D. Bones]

Let's see some photos.

 

[jesuscrisp]

Are you by any chance using an OPA2134 from a sketchy place?

 

[Lukasz]

Both sides works as expected when running separately. Imo looks like stacking those effects require some additional filtering.
I tried 2134 at the beginning, then replace it with 4558 but no difference.

Right now it looks fine, with ~560pF caps, for first stage of both effects. Just wanted to know if there any alternatives to this modification.
I am also not sure how to calculate this filter on opamp stage.

 

[spi]

Imo looks like stacking those effects require some additional filtering.

It shouldn't though. People stack drives all the time and putting them in the same enclosure isn't much different.

I have built the same combo (Mach1+Southern Bell) without issues. It has an order switch, and is quiet in either order.

Photos?

 

[music6000]

How did you connect left PCB to right PCB???

Important: Supplying Pictures when an Issue arises with a PCB Build !!!

I have to raise this ongoing issue when Members ask for Help with an Issue with their Build. I keep repeating this saying '' Pictures are worth a Thousand Words'' !!! Please supply Pictures of PCB & ALL connections ( Footswitch, Input & Output Jacks, Power Jack ) to it along with a clear...

forum.pedalpcb.com

 

[chris.knudson]

I agree with other posters in the thread that photos would be helpful. I'm particularly interested in seeing how the two circuits are connected and grounded.

 

[jesuscrisp]

My guess os there's either something suboptimal about your build or ypur power supply might be noisy. Or your guitar/amp in general.

 

[hamerfan]

I had the same problem some time ago with stacking 2 or 3 different pedals, like Biasb 2 clone, tubescreamer clone, rat clone, Klon clone, Naga Viper clone. Tweaking knobs, using 7 different guitars including Gibson and Fender Custom Shop, changed cables, bought a voodoo lab pedal power 2 plus, used the LPF of a Yamaha FX 500, all configuration are whistling more or less. Since with humbuckers it was little better than with strats and Teles, i never used my stage guitar, a fully copper shielded partscaster. Using that partscaster the problem was gone.