Question about picking up RF.

[LakeFX]

I just finished my first real build, a Green Russian Big Muff from the tagboard layout.  It sounds fantastic and I learned a lot, especially from the debugging guide here.  When plugged into an external wall wart it picks up radio signals.  When plugged into an external battery, it does too, but not as badly.  When powered with the internal battery, it doesn't pick them up at all.  My thought is that this has to do with the battery grounding to the case when inside it.  My question is, how to I fix this when plugged into an external supply?  Do I just run a wire from the power jack to the case?

Thanks!

[armdnrdy]

Use shielded cable for you input and output connections.

RG174/U is pliable enough to use in short pieces. Ground one end of the shield.

[thelonious]

My thought is that this has to do with the battery grounding to the case when inside it.  My question is, how to I fix this when plugged into an external supply?  Do I just run a wire from the power jack to the case?

What Larry said, and also: if you have a multimeter, set it to measure resistance and test resistance from some metal point on the enclosure to everything that is supposed to be grounded---jack sleeve lugs, negative lug on the power jack, PCB ground, etc.---just to make sure that all your grounds are good to go. You should get zero ohms between every point.

[LakeFX]

Thanks for the advice, you guys are great to a noob here!

I checked all the connections and found one ground connection that was about an ohm higher than the others.  Redid that one and it took care of about half the RF issue.  I found some nice thin shielded wire that I'll swap in for the input connection tomorrow.

[peterg]

You can also try adding a low value cap connected from input to ground.

[Brymus]

Another thing you can do is wrap your DC input wires around a ferite ring a few times,or through a ferite tube like the kind that make the lump on game controller wires.

[LakeFX]

Alright, I replaced the input lead with shielded wire and added a 100pF cap between signal and ground.  The wall wart already has a ferrite tube on it.  This took care of most of the RF issue, although there is still some very faint radio signal coming through.  Given this is my first build and it has a lot of wires in a small enclosure, I'm guessing I just wasn't careful enough with the wire routing, but it's good enough I can live with it.

Thanks for all the help!

[Kipper4]

Keeping the wiring as short as possible within the circuit and off board wiring will help alleviate rf interference.
Longer off board wiring acts like an antenna.
Next time I go to my mom pop electronics shop I'm gonna invest in some ferrite beads too. I was all spent up when I was walking away and spotted them in the window display.

[Jdansti]

>Do I just run a wire from the power jack to the case?

Yes, you can run a wire from the negative connection on the power jack to the case. One way to do this is to wrap a bare wire around the threads of one of your jacks on the inside of the case and run the other end to ground. There are also washers with lugs that allow you to do the same thing.

[duck_arse]

you can also try a 100R or so resistor between the input signal and the 100pF cap to ground you added. this makes a real R/C filter for HF.

[thelonious]

(Like this, just to clarify):

[armdnrdy]

I think the fact that the OP is just building a Big Muff got lost somewhere.

Unless all Big Muffs pick up AM radio frequencies...I believe there is something wrong with his build/gear that needs to be discovered and addressed.

With a high gain pedal like a Big Muff, the interference will be amplified.

[LakeFX]

I think the fact that the OP is just building a Big Muff got lost somewhere.

Unless all Big Muffs pick up AM radio frequencies...I believe there is something wrong with his build/gear that needs to be discovered and addressed.

With a high gain pedal like a Big Muff, the interference will be amplified.

It is certainly something wrong with my build because the issue goes away completely when powered by a battery that makes contact with the inside of the case. Again, it's my first build and I didn't see things like the advice to twist wires and keep leads really short until after I wired everything up. I'll probably go back and do those things, but I may move on to another build in the meantime.

[Jdansti]

I picked up radio stations on my BM build until I got it in the enclosure.  Do you get RF with the lid on and everything buttoned up?

[LakeFX]

I picked up radio stations on my BM build until I got it in the enclosure.  Do you get RF with the lid on and everything buttoned up?

I do when using an external power supply, but not with the internal battery power. This is why I'm becoming more certain that it has to do with wire routing.

[tubegeek]

Try putting a ceramic cap of 100 to 1000 pf directly between the + and - pins of the DC in jack. That doesn't do it, it's something pretty weird.

[armdnrdy]

Did you forget to tell us that you live across the street from the local AM radio station that broadcasts at 50,000 watts?

[LakeFX]

Finally got a chance to really sit down and try playing through the pedal and the sustain and tone pots don't seem to be affecting the sound as much as they should.  I also lose signal when the sustain is turned up all the way.  So, now I think I have a short somewhere or something. I think I'm going to measure voltage at some of the components when I get a chance next week, come back here for more help from all of you wonderful folks, and probably redo all of the leads.

I am in a surprisingly good mood about the whole thing because I've been learning so much from the process that I'll be happy even if I scrap the Big Muff and build something else to go in the box.
Thank you all again for your help!

[boogietone]

I am in a surprisingly good mood about the whole thing because I've been learning so much from the process that I'll be happy even if I scrap the Big Muff and build something else to go in the box.
Thank you all again for your help!

Awesome. The first one is pretty much always a scrapper. One option is to take it apart, paying attention to what you have done and how you would do it differently, and rebuilding it.

Welcome to your new addiction  ;-)

[LakeFX]

Awesome. The first one is pretty much always a scrapper. One option is to take it apart, paying attention to what you have done and how you would do it differently, and rebuilding it.

Welcome to your new addiction  ;-)

I just finished pulling the board out and troubleshooting.  I found two mistakes that were really stupid.  The first is that the mid boost/cut switch was wired to pin 3 of the tone pot (as it is supposed to be), but I had reversed the leads from the board so that what was supposed to go to pin 1 was going to pin 3 and vice versa.  I did the same with the sustain pot.  This made both the tone and sustain pots work in reverse, but completely screwed things with the mid boost/cut switch.  On top of that, in trying to squeeze everything into a 1590B enclosure I had bent one of the capacitors on the switch and it was shorting out against another lead.  I took advantage of all this to add the 100R in series with the input and to cut down some of the leads.  I still get a little RF signal, but it is quiet enough that the pedal is usable.  I'm actually shocked that I'm not scrapping it! 

My only issue now is that I have to have the volume all the way up to get unity gain with the bypass, but I think that just has do with the compression of the fuzz circuit and the massive output of my G&L SB-1.  I actually don't have a lot of use for a fuzz pedal, which is why I built it first in case I got frustrated and decided to scrap it.

This hobby really is addicting and I already have the enclosure prepped for my next pedal, which is going to be a clone of a Lotus Designs Snow Job with a switch to change between guitar and bass input and output caps.  I do a lot of computer programming for my day job and part of what makes me really good at it is that when something doesn't work I obsess over it.  I didn't realize how much building pedals would feed that obsession!