Weird synth-like noise when turning guitar volume down?

[tommycataus]

Hey guys, I've not had a very successful couple of weeks building pedals, but I'm determined not to let that put me off!

I've currently got an Axis Face breadboard-tested and now on vero board but not yet in a pedal enclosure. It all works pretty fine until the gain and volume are turned right up and the volume on the guitar is turned completely down. With a high-gain signal running through the pedal and my guitar volume turned right down I get a very loud noise and I'm not sure why it's there.

I've not posted pics or a video yet in the event that anyone recognises this problem and can provide an instant answer... if not I will be happy to upload anything that will help you guys to assist! I appreciate all the help you can give me. Thanks so much.

Tom

[brett]

Hi
it's not easy to be sure but...
it could be that this is turning your guitar into a low impedance antenna. It happens a lot with fuzz/axis/other faces.
You might be listening to the background cosmic radio emissions from the big bang. Seriously. The same as tuning a radio between stations (tho if you are young you might not remember radios with a knob for tuning it manually)
It is likely you can stop it by putting some resistance in-line at the input of the Axis Face. A couple of kohms might be enough. Don't use too much (10 k and up ??) or you'll lose the sweet effect of low input impedance to the Axis Face.
cheers

[Lurco]

http://www.diystompboxes.com/smfforum/index.php?topic=103518.msg922799#msg922799 for more help?

[tommycataus]

Thanks guys, the series resistor did the trick! Lovely jubbly. It's an interesting phenomenon but I'm researching it a bit more so I can understand it. I really appreciate the pointers as all this feedback on this forum is helping me tremendously.

I just have one further question - where can I get shielded input/output wire and what does it look like? Is it the same as the vintage-style braided guitar wire with a braided shield protecting the length of the wire that connects to ground? I've not needed any to date but it seems like the day is fast approaching...

[induction]

Look for rg174 or rg179. I bought some rg174 from Newark a few years ago. You can also find it on ebay and probably plenty of other online stores.

[tommycataus]

You beauty.

[GibsonGM]

You can also get shielded wire from the 'junk bin'.  Look around when taking apart old computers, PA units and the like.  Or from old, dead guitar patch cords you don't trust anymore.  You don't need anything special, just wire with a shield.  Don't use coax, tho, you can get crappy effects from internal capacitance.    I pulled 20 feet of it out of some place or other, and never need to buy any!

[duck_arse]

the "cd to soundcard" cable inside a pc (do they still have them? cd's?) is sheilded

[induction]

You can also get shielded wire from the 'junk bin'.  Look around when taking apart old computers, PA units and the like.  Or from old, dead guitar patch cords you don't trust anymore.  You don't need anything special, just wire with a shield.  Don't use coax, tho, you can get crappy effects from internal capacitance.    I pulled 20 feet of it out of some place or other, and never need to buy any!

Rg6 is standard TV coax. Capacitance is about 16 pF/ft. Guitar cables (which are also coaxial) usually range from 20-50 pF/ft, though Elixir is 11 pF/ft. Rg174 and Rg179 are around 30 pF/ft and 20 pF/ft, respectively. You'll use far less than a foot of the stuff in a pedal (especially compared to the 10' - 20' guitar cord going into it), so I wouldn't worry about the capacitance. It's a tradeoff anyway, since less capacitance also tends to imply less effective shielding. TV coax and guitar cables will work fine. The main benefit of Rg174 or Rg179 is that it is much thinner and easier to work with. Either way, you have to untangle that braided shield, which is a PITA.