My vintage fuzz picks up radio broadcasts ... why?

[GuitarPlayer]

I built a BYOC E.S.V. Fuzz that sounds excellent. However, when I turn the guitar's volume pot all the way down, I can hear a radio broadcast coming out of the amp. It only happens with this Fuzz pedal, and does happen with all of the guitars I have tried so far.

Any ideas on what the cause, and more importantly the fix might be?

Thanks!
Jake

[frequencycentral]

Have a look at this schematic. See the 220pf cap between the base and collector of the first transistor? Remove it and you get a radio receiver. So try adding a similar cap to your build at that point.

.........unless you're picking up vitage radio broadcasts from the 60's!

[biggy boy]

I've recently built two fuzz Face boards and both of mine picked up radio.
I'm hopping once I get them in a stomp box enclosure they will ditch the Muzak!
Apparently good shielding kills the radio.
I also found out from trial and error that changing the cap sizes make a bit of a difference.

[R.G.]

I built a BYOC E.S.V. Fuzz that sounds excellent. However, when I turn the guitar's volume pot all the way down, I can hear a radio broadcast coming out of the amp. It only happens with this Fuzz pedal, and does happen with all of the guitars I have tried so far.

Any ideas on what the cause, and more importantly the fix might be?

It's because the circuit design lacks any immunity to RF and your shielding is not enough to keep it out. Any RF on the input wires is transferred to the first transistor where it's rectified to audio and then continues through as audio.

[FuzzAldrin]

BYOC is clone of the dallas arbiter, right? So their circuit design lacks any RF immunity.
RI happens to alot of people, not just with fuzzes, but whs and distortions and even my phaser.  no big deal

[Gus]

Just another example of cloning and not improving a standard two transistor design from the 60's and maybe even way earlier.  I have a book from 1964 that has the FF type circuit with the math.
  R.G. do you know when the first two transistor and three with the added EF circuit like in the FF and audio preamps was published?

[GuitarPlayer]

Have a look at this schematic. See the 220pf cap between the base and collector of the first transistor? Remove it and you get a radio receiver. So try adding a similar cap to your build at that point.

.........unless you're picking up vitage radio broadcasts from the 60's!

Thanks for the advice. Following are the schematic and wiring diagram. I'm trying to determine the easiest/best way to add a 220pf cap. Anyone have any  suggestions?

[frequencycentral]

Between nodes 4 and 9. 

[GuitarPlayer]

Between nodes 4 and 9. 

I was hoping for a little more detailed suggestion 

I don't know if I need to modify the PCB or what? Drill holes, cut a trace, or
I don't want to ruin it, but would like to eliminate the radio 

[Gus]

You can solder the cap leads at the back of the board at the pads for nodes 4 and 9.

Did you ask at the BYOC forums?

There are other things you can do for RF.

[GuitarPlayer]

^^^^ Thanks Gus.

No, I haven't asked at the BYOC Forum. I couldn't get the site to come up earlier, but will try again now and search there too. Maybe someone has already posted a recommendation there.

Regards,
Jake

[Mick Bailey]

I've had similar problems with vintage designs and have generally found that a small value ceramic cap right across the input socket (signal input to ground) cures it. This can be as low as 47pf. Try experimenting with values to get the lowest value cap that will cut the radio but not noticeably affect the treble.

[GuitarPlayer]

I've had similar problems with vintage designs and have generally found that a small value ceramic cap right across the input socket (signal input to ground) cures it. This can be as low as 47pf. Try experimenting with values to get the lowest value cap that will cut the radio but not noticeably affect the treble.

Thanks Mick!

[Paul Marossy]

I've had similar problems with vintage designs and have generally found that a small value ceramic cap right across the input socket (signal input to ground) cures it. This can be as low as 47pf. Try experimenting with values to get the lowest value cap that will cut the radio but not noticeably affect the treble.

+1

[R O Tiree]

If Mick Bailey's suggestion doesn't work, solder a 220pF cap onto the pads of Q1's base and collector on the other side of the board from the rest of the components. You'd be well advised to snip the leads to about 1/4" long

Remove Q1 from its socket (probably best to remove Q2 as well - mark with a fine Sharpie which one came from which socket). Looking at the pic you posted, there's a triangle of pads inside Q1's circle. The base is the "top" pad of that triangle. The collector is the bottom left-hand pad of the triangle as we're looking at it (obviously, when you turn the board over to get at the "solder-side" look for the right-hand pad...).

Solder one leg of the cap onto the base pad, allow it to cool, then bend/tease the other leg of the cap so it touches the collector pad and solder that joint.

Once you've soldered the cap into place, replace the 2 transistors in their sockets and your fuzz should be radio-free.

If you're at all unsure about what I mean, post back a pic of the other side of the board and I'll mark it up for you.

[earthtonesaudio]

Another vote for the feedback cap (from collector to base of Q1) rather than the cap-to-ground.  Sometimes the cap-to-ground approach makes it a better radio.