radio interference

saildoctor · 7944

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Offline saildoctor

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on: December 27, 2012, 06:30:46 PM
I finished my Tode build!  Works great with one catch... it picks up the radio pretty well.  The local NPR station to be exact!  If I coil the cable from my guitar just so I can occasionally make the signal go away.  I'm using a Classic Vibe Telecaster thinline (mahogany!) with single coil pickups.  Do you think it is mainly occurring because the guitar isn't shielded?  I do have another amp I've played it with and it didn't have this issue.  I've poked around inside the Tode to see if I missed a ground connection, and tried soldering a 100uH RF choke inline with the input hot.  Any ideas on what I should look at?  Thanks!

Kerry Sherwin

45 Paramounts, 6SN7 Extended FPIII, OC3 regulated Seduction
Blumenstein Orca Deluxe / 2x Orca Subs
VPI Classic / ADC CD-100x


Offline Doc B.

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Reply #1 on: December 27, 2012, 06:35:37 PM
Does it pick up the station when the guitar cable is unplugged?

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline saildoctor

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Reply #2 on: December 27, 2012, 06:51:32 PM
Doc, no it doesn't pick up radio with the cable unplugged.  It does have a fair amount of hum with nothing plugged in though.

Kerry Sherwin

45 Paramounts, 6SN7 Extended FPIII, OC3 regulated Seduction
Blumenstein Orca Deluxe / 2x Orca Subs
VPI Classic / ADC CD-100x


Offline Doc B.

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Reply #3 on: December 28, 2012, 06:27:10 AM
That indicates two things - the amp being quiet when you unplug the cable means the pickups or cable are acting as an antenna. The input grid resistor of Tode is extremely high at 10 Megohms and this can make it very sensitive to stuff that another amp might not pick up. I don't have trouble with it with my guitars, but I don't live near a transmitter either. You might try shielding the guitar pickups. Along with shielding the pickup cavities, on my short scale strat I put a wrap of copper foil around each pickup coil, not a complete wrap, but with a gap that is connected with teflon tape. A full wrap that overlaps will kill the top end. Each wrap is tied to the other cavity shielding with a soldered wire. That guitar is super quiet for a single coil guitar and still has a good top end.

Cables could certainly make a difference too, though my Todes have been quiet with everything from $5 Monoprice cables to the truly great sounding Shunyata Pro guitar cable.

The buzz - from my own experience I will guess this is about your power connections. At the office where we have relatively recent, up to spec wiring a Tode is super quiet. At home where our power grounding is ancient and needing repair the amp does buzz a little bit. Try using the amp at different places and see if the buzz is different.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline saildoctor

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Reply #4 on: December 29, 2012, 08:58:42 AM
Thanks - I'll try shielding the pickups too as you suggest.  I was going to try doing so to the cavities eventually anyway.  Any pictures of your technique?  Does the foil wrap around the side edges only or cover the back/bottom as well?

I'm pretty sure my building's wiring is ancient crap.  One of our in-wall light switches gave up the ghost not too long ago - maybe that means the landlord will pony up for an electrician to come over and jazz up our wiring a bit!

Kerry Sherwin

45 Paramounts, 6SN7 Extended FPIII, OC3 regulated Seduction
Blumenstein Orca Deluxe / 2x Orca Subs
VPI Classic / ADC CD-100x


Offline Doc B.

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Reply #5 on: December 29, 2012, 04:14:37 PM
Sorry, don't have a photo handy. The foil should line the entirety of the individual cavities. The pickguard should have foil on the backside that contacts the foil in the cavity, and all should be interconnected and tied to the ground connection of the output jack. The shield foil around each single coil pickup should also have a drain wire to the ground of the output jack.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.