Custom FV-1 Pedal Problems

[AineeJames]

Hello everybody,

I have been working on designing and building my own pedal using the FV-1 and I am having some problems getting my signal to be affected. At the moment, all I hear is a humming noise-type sound when my guitar is plugged into the input. However, as I flip through the effects, I can hear the internal ROM effects affecting this noise. For example, when I change to internal program #3 I can use POT0 and hear the pitch change in the noise. I suspect that I have a problem with the input stage leading to the FV-1 but I am blind to the issue at the moment and was hoping to get some help! I've attached a picture of my schematic to this forum to give a frame of reference.


As far as I know, so far, the rest of the circuit works and I properly see which prg I've selected on my 7-Segment display.

I would appreciate any help you guys have to give!

[bartimaeus]

if you hear the FV1 affecting the noise, to me that sounds like the FV1 is working, and your input signal is the issue.

looking at the schematic, it mostly seems good. but checking the very first component shows the issue.

R4 is connected wrong. i assume this was meant as a pulldown resistor? instead, you wired it to prevent the input jack's sleeve from connecting to ground. no wonder you get a (ground) hum.

i also don't see any connections for the opamp rails. i can only hope those are wired up correctly? EDIT: my bad, just didn't see it.

also, your setup for the volume control is a bad idea. the pot RV2 forms a lowpass filter with C8. with the pot at max (100k), you get a lowpass filter at 7234Hz, which kills a ton of your treble. you'd be way better off just adding the pot as a standard volume control before R16.

i'd also suggest sticking R5 on the other side of C5. that will further reduce any switch pop.

[AineeJames]

Oh shoot, would you recommend I get rid of the pull-down R4 altogether and just directly ground it?
Also, great input on the volume knob, that was a big oversight on my part lol.

I really appreciate all the help! This is the first guitar pedal I have built so I've just been referencing all sorts of different designs.

[antonis]

You can wire R4 on the left leg of C5..

[bartimaeus]

Oh shoot, would you recommend I get rid of the pull-down R4 altogether and just directly ground it?
Also, great input on the volume knob, that was a big oversight on my part lol.

I really appreciate all the help! This is the first guitar pedal I have built so I've just been referencing all sorts of different designs.

you need to directly ground the sleeve of the input jack, just like you did with the output jack.

as for R4, you can wire it like R22 and it will work as a pulldown (following antonis's advice). or you can remove R4, but only if you swap the locations of R5 and C5. see this article for an explanation: https://www.mrblackpedals.com/blogs/straight-jive/6629778-what-really-causes-switch-pop

you may think this is unnecessary since you don't have a footswitch connected to those jacks, but your current setup can cause switch pop from other pedals if you connect other true bypass pedals to this one.

if you already made a PCB, the easiest thing would be to jumper R4 (replace it with a wire). then put R5 in the holes for C5, and put C5 in the holes for R5.

EDIT: i'd similarly recommend swapping R18 and C13, so the output jack is not connected directly to a capacitor. (the only time i wouldn't is if you're using an NE5532 opamp instead of a TL07x, because the NE5532 dislikes being connected directly to a capacitor).

[mark2]

EDIT: i'd similarly recommend swapping R18 and C13, so the output jack is not connected directly to a capacitor. (the only time i wouldn't is if you're using an NE5532 opamp instead of a TL07x, because the NE5532 dislikes being connected directly to a capacitor).

Can you talk a little more about why you don't want the capacitor directly on the jack?

[antonis]

see this article for an explanation: https://www.mrblackpedals.com/blogs/straight-jive/6629778-what-really-causes-switch-pop

Mr Black's "aspect" has been in dispute at every turn..

[bartimaeus]

EDIT: i'd similarly recommend swapping R18 and C13, so the output jack is not connected directly to a capacitor. (the only time i wouldn't is if you're using an NE5532 opamp instead of a TL07x, because the NE5532 dislikes being connected directly to a capacitor).

Can you talk a little more about why you don't want the capacitor directly on the jack?

capacitors leak voltage. it can be just a tiny bit, but connect that to a switch and you can get a pop.

adding a "pulldown" resistor will allow that voltage to flow to ground, but it takes time if the resistor value is high (and it needs to be to prevent signal loss). that's why pedals often pop for a few minutes after they are first powered up.

adding a "series" resistor limits how much of that voltage can ever reach the jack (and any switches that jack may eventually connect to). so it limits how load a pop can ever be.

whenever i check the schematics for pedals with minimal pop, they always have either those resistors. for example, the aion emerald. it has a 10k resistor on the input. it also has a volume pot on the output, which you can think of as a combination of a series resistor and a pulldown resistor. https://aionfx.com/app/files/docs/emerald_documentation.pdf

see this article for an explanation: https://www.mrblackpedals.com/blogs/straight-jive/6629778-what-really-causes-switch-pop

Mr Black's "aspect" has been in dispute at every turn..

i figure it's clear for a beginner though

[amz-fx]

6 Reasons Guitar Pedals Pop When Switched

http://www.muzique.com/lab/pop.htm

Best regards, Jack