Faint effect noise when in bypass mode

[Sterik]

Hello there! This is my first post on this forum. A little something about myself: I'm from the Netherlands and I have been playing guitar for about 8 years and I recently started tinkering with electronics because it seemed like a fun thing to do (and it is!) and because I wanted to make some pedals for myself and as a gift for guitar playing friends. I read all the rules for making a new thread etc. so I hope that this question is a good one, and I'm sorry if I forget something. I would really appreciate it if some of you could help me out!

Anyway, I have been working on this pedal for the past two weeks, and I simply can't get it to work properly. It's quite maddening actually. The pedal I'm doing is a Fuzz Factory, the schematic can be found here: http://2.bp.blogspot.com/_y4AYtND8Hz8/TCINTn3D6JI/AAAAAAAAAY0/wBxmQy75fJ8/s1600/knownworkingtotal.gif

I built the board exactly as shown, and I know something is right, because when I engage the pedal, everything seems to work fine. 80% of the sound is noise and screeching, and the other 20% are nice fuzz sounds (like the Fuzz Factory is supposed to ). I'm using a 6 pin DPDT switch to make it true bypass. I've grounded the negative wire of the 9v DC jack and the negative output of the board (where is says ground) to the input and output jacks, which are metal so they connect with the enclosure (tested those so I know they are connected properly to the enclosure)

However, when I turn it off, a faint effect can still be heard. When turning the potentiometers, I still get screeching and it can go pretty loud too, however not as loud as when the pedal is engaged. I know that the bypass is working, because when I remove the power altogether, I get a nice clean sound with no tone loss. I measured everything with a multimeter like 10 times, and I checked that everything is wired properly about 10 times more. I'm not an expert on electronics or anything, so it's hard for me to tell if there could be anything wrong with the schematics.

Does anyone have the faintest idea about what this can be? I feel like I have done everything I can, so this is probably my last resort.

[Seljer]

Theres enough capacitive coupling between the contacts and wires for the signal to creep through. I've made a delay thats capable of self-oscillation that has the same issue.

You may be able to mitigate this slightly by using wiring scheme for the switch that grounds the input of the circuit when bypassed (though this may not help if the pedal still make screeching noises even without an input signal) https://www.generalguitargadgets.com/pdf/ggg_sw_3pdt_tb_gi_bat.pdf <- observe how the olive coloured wire from the input is run diagonally over the switch

[peterg]

Welcome to the forum Seljer. Please see the attached thread for debugging. Pictures of your work will help. Are you sure you've wired the switch properly?

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[darron]

As said, capacitance can bleed through some signal through wires or through the switch. I might have a solution for you.


It might be that the circuit is going nuts and creating loud oscillation when you disconnect the audio signal in bypass and leave the input floating. Try connecting the circuit input to earth with a wire while the effect is in bypass mode and see if your noise problem goes away. This is common practice with a 9 pin 3pdt bypass foot switch.


Edit: ps, you don't need to solder the wire in or anything. I just meant a quick test by hand to see what the result is.

[Sterik]

Thanks a lot for the (quick) replies! I didn't ground the input as suggested, but used the most basic version (using a jumper between the outer 2 pins on a 6 pin switch) for the bypass.

I will try this tonight and I'll let you know when I get any results.

[Sterik]

The input grounding worked! The pedal is now clean as a whistle 

Thanks a lot for the input

[darron]

Awesome

I've got some true bypass layouts up here:

http://www.dazatronyx.com/tech/what-is-true-bypass/