Hi all,

Decided not so long ago to build myself an FV-1 pedal to play around with, and thought I'd go all out and try 'designing' a PCB for it too - I'm a total beginner, so I pretty much winged it and looked to this forum, other schematics and other PCBs for help. It's worked pretty well, dry signal goes in, and effected signal comes out just fine.

However, there's this constant buzzing noise which I am almost certain is a grounding issue, I can't see what else it would be. I'd like to share my PCB design with you guys to see if it's an issue with the design itself that's causing the ground issues, or if I need to look elsewhere. I've also noticed that the noise is reduced if I touch the metal on my amp, which is very peculiar to me and I'm not sure if that's something big to be concerned about or not.

Also, if anybody has any general tips on PCB design or comments on my design, I'd love to hear them. I'm expecting that this PCB might have other issues since this is my first design ever with fairly little electronics knowledge.

Schematic:


PCB Top Layer:


PCB Bottom Layer:


Thanks in advance for the help

Pin 5 U2.2 sure needs a resistor to 4.5V.

If touching the amp changes the buzz, we need to see your off-board wiring and enclosure.

Hi Josephfra,

Quote from: josephfra on December 01, 2020, 01:28:40 PM
Also, if anybody has any general tips on PCB design or comments on my design, I'd love to hear them. I'm expecting that this PCB might have other issues since this is my first design ever with fairly little electronics knowledge.

Firstly, I think that's a very good effort for a first PCB, so well done! Mine was a lot uglier!

I've got one comment for a "Version two" if you decide to ever do one. You've used a passive mix of the two signals, and then both dry and wet signals have buffers in front of them (which is generally sensible) but in this case, the dry signal is buffered on the way in, and then buffered *again* before the passive mix. It might be better to go for a different mixer circuit, like the one shown in the box on the left on page one here:

http://www.geofex.com/Article_Folders/panner.pdf

The values are mentioned in the text - 15K, 10K and 51K for the feedback resistor. This circuit is very useful for all sorts of "either/or" mixing jobs where you need A or B or some amount of each, but not 100% of both at the same time.

The big advantage of this is that it would save you two op-amps and allow you to use a dual package instead of a quad.

HTH!

If you're interested in ElectricDruid's mixer recommendation, you can see a specific implementation of it (on an fv-1 no less) that works really well in the Arachnid pedalpcb board: https://www.pedalpcb.com/docs/Arachnid.pdf

I lifted and used it in my pedal with good results too.

+1 on the arachnid setup , i have that same schemo on breadboard and works fine....

Well I figured out the issue. Turns out I put the footprints for my jacks on the PCB backwards. 
Tested it by wiring some other jacks up quicky, and sure enough all the noise was gone. Now I've got to desolder the PCB mounted jacks I'm using... wish me luck.

Thank you all for the advice with the mixer! I'll definitely be using it if I make a similar circuit again.

Quote from: PRR on December 01, 2020, 01:41:47 PM
Pin 5 U2.2 sure needs a resistor to 4.5V.

I see - what would this resistor do? Or is that something I'd just need more knowledge on op-amps in general to understand? It's probably time for me to pick up a book or something anyway.

Quote from: josephfra on December 03, 2020, 09:14:05 AM

Quote from: PRR on December 01, 2020, 01:41:47 PM
Pin 5 U2.2 sure needs a resistor to 4.5V.

I see - what would this resistor do?

Just to bias op-amp non-inverting input..
(take a look on U.1 & U2.3 respective  non-inverting (+) inputs.. - U2.4 is "directly" biased (DC coupled) from U2.1 voltage follower output..)

Op-amps need a DC reference point for signal to symmetrically swing (up & down) 'cause they actually are differential amps..
(NFB tries to make inputs difference zero -> both inputs at the same voltage..)

https://ocw.mit.edu/courses/media-arts-and-sciences/mas-836-sensor-technologies-for-interactive-environments-spring-2011/readings/MITMAS_836S11_read02_bias.pdf
https://www.renesas.com/us/en/document/apn/how-bias-op-amps-correctly
https://www.analog.com/media/en/technical-documentation/application-notes/AN-581.pdf


P.S.
Delayed Welcome..

Ah, I see. Thanks for the recourses, I'll be studying them.

And thanks for the welcome! No worries about the delay

The board looks very good.
I would refine a few points
1) The contacts of the FV-1 chip that connect to the ground plane, you have several contacts that are located next to each other and the connection to the ground, in theory, can form jumpers when soldering the chip.
these are contacts 11 + 12 and 24 + 25
2) Pins 1 and 2 also have a track between the pins, it is usually recommended to place the track in an arc under the chip or in front of the chip to prevent the appearance of jumpers.
3) There are clearly polygons under the chip that are not connected to anything, I would configure the program to delete such polygons.
4) The tracks have unnecessary bends, for example the track between R1 and C9 can be made straighter and some other tracks too.
5) It is recommended to place the components in one position, at least it is more convenient to solder this way and the board looks more pleasant.
6) Both sides of the board use a ground plane, I know that this has no problems with analog circuits and you can safely install a ground on one side only, or on both sides, but I'm not sure if this is normal for digital circuits.
7) Not sure if this is important for manual soldering, but in any case, board manufacturers recommend installing polarized components in one direction, although I have seen exceptions on commercial boards, large manufacturers.

Great idea to get some inspiration from the pedalpcb board! Those are the circuits I was mostly referencing when putting together this layout..

https://oshwlab.com/tomsouthtrader/fv-1-module

Though I have been hesitant sending off this design, mostly as it will be only the second time I have made a pcb and had it assembled using JLC's SMD Assembly service.
Also I am wondering about my use of tantalums in the audio path and my ground planes..

Also I had made out this mixer circuit on breadboard to find that the volume of seems to drop at 100 percent wet =/

And I'd like to add more thanks to antonis, as I will now also be doing alot of op amp related reading