Foxx Tone Machine Noise (Octave off)

[slashandburn]

Hey all, Hope everyone's well. Hoping to pick your brains about the Tone Machine Octave switch.

Built on this layout: http://2.bp.blogspot.com/-j0CWtKRRwx4/VaAY56SoaUI/AAAAAAAAFbE/PAQoux4DsT8/s1600/fOXX%2BTone%2BMachine.png

I'm finding it a bit noisier with the Octave turned off. Just typical high-gain pedal noise, no a dealbreaker but I'm curious all the same.  Is there a reason this would happen? I see the switch essentially lifts on of the diode legs, so I'm wondering if the lifted.leg could be the source of the noise (Russian D9K germanium diodes) or whether the octave engages some kind of HP filter that eliminates the noise.

Or if it's more likely I've bollocksed something up.

Cheers
Iain

[iainpunk]

i think its because the higher current running through the diode when the octave is off. more current often generates more noise in germanium diodes.
i think you don't need to have low forward voltage diodes anyway, because they are forward biased anyway.

cheers,
Iain

[slashandburn]

Thanks man,

I'll try out silicon diodes in that role and see what happens. I went to town with shielded wire and managed to reduce the overall noise, just struck me as really odd that it's still much noisier with the Octave off. Almost as lifting that diode leg leaves it acting as an antenna.

Cheers Iain! Hope you and yours are well.
Iain

[antonis]

Also, try to place thw switch on diode cathode..

[slashandburn]

Sadly Silicon diodes didn't solve the noise, I will try Antonis suggestion of moving the switch, and if that doesn't work I'll either look at a different layout or (more likely) just accept it and move on.

It's not ridiculous levels of noise at all, just strikes me as odd that it's only noticeable with the octave off and with the octave on its near silent.

[anotherjim]

I've got an idea. There's a phase splitter. With both phases mixing together, the common mode noise cancels. Remove one phase and that cancellation stops. Not a lot you can do if that's the case.

[radio]

How about bridging both diodes with a switch? The sound will get louder

not sure that will be a negativ issue

[pinkjimiphoton]

the prob is noisy transistors. they may have been damaged slightly soldering.

when the diodes are in, they are phase cancelling most of the fundamental, thats what makes the octave pop. when they're out, its like a split humbucker.

if ya gotta dpdt, set you can experiment with adding a small cap to ground either before q1 or where ever the noise is from b, or add a cap between b and c. usually its only one transistor that will really be noisy.

adding the small cap can help nuke the noise, if ya use a 2pdt or 3pdt switch for the octave, use an unused section to turn the cap on/off so that when the octave is in, there's no cap, and when its off, it automatically nukes the noise down some.

[slashandburn]

Brilliant stuff, thanks folks!

Jimi hit the nail on the head. A small cap from C to B on Q3 pretty much nuked the noise entirely. I'm not convinced the tranny was damaged though since replacing all four did nothing.

Starting to wish I had a scope (and the knowledge to use one properly) to really nail down the source of the noise.

But huge thanks again everyone. All is well that ends well.

Cheers
Iain

[pinkjimiphoton]

you can get an affordable digital oscilloscope diy kit on bangood.com for about 50 bux or less.
i built it, came out great. i dunno how to USE it, lol, but i got it!

https://usa.banggood.com/Digital-Oscilloscope-DIY-Kit-DIY-Parts-Electrical-Digital-Oscilloscope-Pocket-size-Handheld-Electronic-1Msps-p-1909809.html?cur_warehouse=CN&rmmds=search

[slashandburn]

you can get an affordable digital oscilloscope diy kit on bangood.com for about 50 bux or less.
i built it, came out great. i dunno how to USE it, lol, but i got it!

https://usa.banggood.com/Digital-Oscilloscope-DIY-Kit-DIY-Parts-Electrical-Digital-Oscilloscope-Pocket-size-Handheld-Electronic-1Msps-p-1909809.html?cur_warehouse=CN&rmmds=search

Nice one Jimi!  I'll look into that. Brace yourself for the inevitable "Help! First real smd build: My DIY Oscilloscope isn't working and I've melted all my fingers off" post in around 6 months.

[pinkjimiphoton]

hahahahh.... the smd stuff is all pre-done on this !