Author Topic: R.F. Interference....Slight Return  (Read 867 times)

Big Monk

Re: R.F. Interference....Slight Return
« Reply #20 on: March 17, 2021, 07:40:55 AM »
Does it help to screw the bottom cover on?

It usually sits on top of the plate but I have not been putting the screws on. Would that help?

It should help ensure good contact since aluminum normally has a coating of non-conductive aluminum oxide on it and screwing the cover on may enable the metal to bite through the oxide. I suspect the test points are also acting as antennae so cutting them temporarily to check on this may prove useful.

First thing i'll try today!
We are what we repeatedly do. Excellence, therefore, is not an act, but a habit. Aristotle

"Beneath the bebop moon, I'm howling like a loon, for you..." Marc Bolan

Big Monk

Re: R.F. Interference....Slight Return
« Reply #21 on: March 17, 2021, 02:45:06 PM »
Ok. Quick Update.

It should help ensure good contact since aluminum normally has a coating of non-conductive aluminum oxide on it and screwing the cover on may enable the metal to bite through the oxide. I suspect the test points are also acting as antennae so cutting them temporarily to check on this may prove useful.

So first thing I did was clean up the circuit. I shortened leads and redid all the connections to be more compact. Then I removed the test points from the enclosure and screwed the bottom plate on securely. Fired it up and no change.

First short out the input to confirm the RF is getting into the input.
It's an OK assumption but it might not be true.

After my first pass, I shorted tip to sleeve on the input jack and the condition persisted. It did.

Another thing which occurred to me is maybe the hole in the system is the guitar wiring.  RF is actually
getting into the guitar wiring and you are trying to fend it off with filters at the amp and pedals.
Shielded cavities and wires in the guitar help by there's still the pickups.   It's not so easy to determine
if it is getting into the guitar or the pedal input.  You could make 6.5mm socket with short and plug
the guitar end of the lead into that.  If the RF goes away it's not 100% conclusive it's the guitar,
since it could be getting into the pedal input and short helps that case as well.   If you short the
input at the pedal and the RF is still present then clearly it's getting in somewhere else.

So moving on to Rob's suggestions above, two things became immediately apparent:

1.) I have a significant amount of nasty buzz (think ground issue) when not touching the strings on the guitar. I realize some buzz here is normal but this is significant.

2.) RF is reduced, along with the nasty buzz, when i plug in my other guitar.

So, it seems the wiring in the brand new guitar is suspect! Rookie mistake trusting that something new was not a contributor.

EDIT: It seems like the issue changes by the second, as i played my other guitar for a few more minutes and while hum and
RF were reduced, they were still there. I can't figure out what the hell it is. The circuit sounds killer but the RF is killing me. I guess tonight or tomorrow i'll try some of the things previously shown to work, i.e. series resistance and RC filters.
« Last Edit: March 17, 2021, 02:56:29 PM by Big Monk »
We are what we repeatedly do. Excellence, therefore, is not an act, but a habit. Aristotle

"Beneath the bebop moon, I'm howling like a loon, for you..." Marc Bolan

Big Monk

Re: R.F. Interference....Slight Return
« Reply #22 on: March 17, 2021, 03:07:56 PM »
Something just occurred to me.

I do all my testing on this little guy:



I'm wondering is this may be the culprit. Guitar buzz seems equivalent between my 2 guitars.

This thing is basically in a plastic case. I'm curious to see if shorting the output of the Fuzz Face still has RF present. That would lead to the mini-amp, correct?
« Last Edit: March 17, 2021, 03:09:28 PM by Big Monk »
We are what we repeatedly do. Excellence, therefore, is not an act, but a habit. Aristotle

"Beneath the bebop moon, I'm howling like a loon, for you..." Marc Bolan

garcho

Re: R.F. Interference....Slight Return
« Reply #23 on: March 17, 2021, 03:34:25 PM »
Quote
I'm curious to see if shorting the output of the Fuzz Face still has RF present.

DON'T short outputs, basically, ever
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Big Monk

Re: R.F. Interference....Slight Return
« Reply #24 on: March 17, 2021, 03:45:40 PM »
Quote
I'm curious to see if shorting the output of the Fuzz Face still has RF present.

DON'T short outputs, basically, ever

You are correct. I think what I was trying to say is test the post effects part of the chain to check the amp.
We are what we repeatedly do. Excellence, therefore, is not an act, but a habit. Aristotle

"Beneath the bebop moon, I'm howling like a loon, for you..." Marc Bolan

Rob Strand

Re: R.F. Interference....Slight Return
« Reply #25 on: March 17, 2021, 06:41:39 PM »
Quote
This thing is basically in a plastic case. I'm curious to see if shorting the output of the Fuzz Face still has RF present. That would lead to the mini-amp, correct?

If you have something else to plug in to it would be good.  Even an old set of PC speakers.

Buzz problems are often caused by shielding.    Technically I wouldn't put these in the RF interference category since the source of the noise is usually mains wiring.    The mains wiring is like a noisy source connected to one plate of a capacitor, the mains wiring itself.  The other side of the capacitor is the metal surfaces in you equipment.   The dielectric of the capacitor is the air in between.

Quote
I have a significant amount of nasty buzz (think ground issue) when not touching the strings on the guitar. I realize some buzz here is normal but this is significant.
Ungrounded equipment can promote this for sure.   Normally most of the mains borne noise goes down the ground and the larger area of grounded metal around help this.   When the ground path is removed the noise will happily couple in both the signal lines and the ground line.

If you can connect a ground wire to your rig you might find it all comes good.

Some DC adaptors can promote noise.   The fact they connect to the mains can be enough to promote buzz coming through.   That's often why powering from batteries has less tendency to cause noise issues.

OH, RF filters at the input and most of the stuff discussed previously will not help buzz coupled in from the mains or through the air from the mains wiring.    RF filters stop radio stations breaking into the audio.    Think of pips from your mobile phone (although those issues need to be solved a little differently to AM radio as the frequencies are quite different).

 
« Last Edit: March 17, 2021, 06:52:01 PM by Rob Strand »
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Big Monk

Re: R.F. Interference....Slight Return
« Reply #26 on: March 17, 2021, 08:07:39 PM »
Quote
This thing is basically in a plastic case. I'm curious to see if shorting the output of the Fuzz Face still has RF present. That would lead to the mini-amp, correct?

If you have something else to plug in to it would be good.  Even an old set of PC speakers.

Buzz problems are often caused by shielding.    Technically I wouldn't put these in the RF interference category since the source of the noise is usually mains wiring.    The mains wiring is like a noisy source connected to one plate of a capacitor, the mains wiring itself.  The other side of the capacitor is the metal surfaces in you equipment.   The dielectric of the capacitor is the air in between.

Quote
I have a significant amount of nasty buzz (think ground issue) when not touching the strings on the guitar. I realize some buzz here is normal but this is significant.
Ungrounded equipment can promote this for sure.   Normally most of the mains borne noise goes down the ground and the larger area of grounded metal around help this.   When the ground path is removed the noise will happily couple in both the signal lines and the ground line.

If you can connect a ground wire to your rig you might find it all comes good.

Some DC adaptors can promote noise.   The fact they connect to the mains can be enough to promote buzz coming through.   That's often why powering from batteries has less tendency to cause noise issues.

OH, RF filters at the input and most of the stuff discussed previously will not help buzz coupled in from the mains or through the air from the mains wiring.    RF filters stop radio stations breaking into the audio.    Think of pips from your mobile phone (although those issues need to be solved a little differently to AM radio as the frequencies are quite different).

Just to be clear: the Buzz is less of a concern than the serious twang Im getting from RF. Im just about done assembling my first tube amp in some time and I will table this until Im finished.
We are what we repeatedly do. Excellence, therefore, is not an act, but a habit. Aristotle

"Beneath the bebop moon, I'm howling like a loon, for you..." Marc Bolan