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DIY Stompboxes => Building your own stompbox => Topic started by: Big Monk on March 16, 2021, 03:05:57 PM

Title: R.F. Interference....Slight Return
Post by: Big Monk on March 16, 2021, 03:05:57 PM
Well, I'll be damned if over the last few days I have not searched all over this forum, found countless posts on R.F. and how to stop it getting in, implemented them, and still get the local country station coming through my amp.

I've tried B-C caps, input to ground caps, RC networks on the input, etc.

My breadboard setup exists INSIDE an enclosure, with shield input and output cables, etc. I've tried to route clean and keep leads short, etc.

Am I missing something? Am I just in an area with strong signal?
Title: Re: R.F. Interference....Slight Return
Post by: Fancy Lime on March 16, 2021, 03:30:35 PM
Have you seen the South Park pilot episode? Or could it be coming through the guitar? I recently put the input jack into the breadboard the wrong way round, so that the guitar shield was signal and the signal wire went to ground. I got extreme noise from all nearby electronics until I found the error.

Cheers,
Andy
Title: Re: R.F. Interference....Slight Return
Post by: Big Monk on March 16, 2021, 03:38:17 PM
Have you seen the South Park pilot episode? Or could it be coming through the guitar? I recently put the input jack into the breadboard the wrong way round, so that the guitar shield was signal and the signal wire went to ground. I got extreme noise from all nearby electronics until I found the error.

Cheers,
Andy

I just swapped out the input jack last night so I know that's right. I'll double check the output jack.

Shield wire should be good. I went Shield/Conductor to Input jack sleeve/Tip and conductor to switch. Switch has conductor on switch side and conductor and shield to circuit. Same for output. What's interesting is that some of the capacitor and resistor suggestions to mitigate R.F. actually made it worse, i.e. intensified the pickup.

I'm stumped. Granted, I understand that sometimes this issue can leave you permanently stumped, i.e. try as you may you never mitigate it.
Title: Re: R.F. Interference....Slight Return
Post by: antonis on March 16, 2021, 03:43:07 PM
still get the local country station coming through my amp.

Maybe a local country notch filter would help..  :icon_wink:

(https://i.imgur.com/UNsScNx.png)

Title: Re: R.F. Interference....Slight Return
Post by: Big Monk on March 16, 2021, 03:51:59 PM
still get the local country station coming through my amp.

Maybe a local country notch filter would help..  :icon_wink:

(https://i.imgur.com/UNsScNx.png)

One can only take so much twang..... ;)

What i think i'll do is remove the B-C capacitors and the capitor across the top of the Q2 voltage divider (i'm working on a Fuzz Face right now) while i audition transistors. I may need to play a round a bit to get the set i like and then i can return to frequency and R.F mitigation techniques.
Title: Re: R.F. Interference....Slight Return
Post by: antonis on March 16, 2021, 03:54:22 PM
some of the capacitor and resistor suggestions to mitigate R.F. actually made it worse, i.e. intensified the pickup.

That strongly leads to what Andy above said.. :icon_wink:
(instead of RF sinking you have RF sourcing..)

Or perhaps you use RC filter "conventional" grounding for a positive ground circuit..

P.S.
Could you post a schematic of particular FF work just to leave out some kind of junctions rectification possibility..??
Title: Re: R.F. Interference....Slight Return
Post by: Big Monk on March 16, 2021, 04:32:32 PM
some of the capacitor and resistor suggestions to mitigate R.F. actually made it worse, i.e. intensified the pickup.

That strongly leads to what Andy above said.. :icon_wink:
(instead of RF sinking you have RF sourcing..)

Or perhaps you use RC filter "conventional" grounding for a positive ground circuit..

P.S.
Could you post a schematic of particular FF work just to leave out some kind of junctions rectification possibility..??

It痴 a big standard NPN Fuzz Face. I followed the Axis Face schematic from Fuzz Central so there are some capacitors in various places.

Here is the build:


(https://i.postimg.cc/94vn1Pwc/7027-CB0-D-0-B27-48-CB-B8-AC-5-C994-D99-B9-D8.jpg) (https://postimg.cc/94vn1Pwc)
Title: Re: R.F. Interference....Slight Return
Post by: amptramp on March 16, 2021, 04:55:14 PM
Does it help to screw the bottom cover on?
Title: Re: R.F. Interference....Slight Return
Post by: antonis on March 16, 2021, 04:58:52 PM
Does it help to screw the bottom cover on?

I suspect not, Ron..
(can't see any enclosure grounding point..)
Title: Re: R.F. Interference....Slight Return
Post by: Big Monk on March 16, 2021, 05:09:05 PM
Does it help to screw the bottom cover on?

I suspect not, Ron..
(can't see any enclosure grounding point..)

The pedal sits on top of the bottom plate when in use.

The input jack is grounded against the Chassis mechanically.
Title: Re: R.F. Interference....Slight Return
Post by: Big Monk on March 16, 2021, 05:10:32 PM
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?
Title: Re: R.F. Interference....Slight Return
Post by: PRR on March 16, 2021, 05:25:19 PM
> Am I just in an area with strong signal?

What's on your radio? TV? (over the air) Landline telephone? When I was a half mile from a 50,000 Watt AM station I could hear it on any loose contact, without amplification.

Now we have Wifi and cell and door-cams and my toilet is bugged......
Title: Re: R.F. Interference....Slight Return
Post by: mozz on March 16, 2021, 05:45:49 PM
House wiring maybe? You can always file a complaint with the FCC, they may be running over power or wrong direction, maybe over modulated.
Title: Re: R.F. Interference....Slight Return
Post by: PRR on March 16, 2021, 06:07:38 PM
> file a complaint with the FCC

It would take a lot more than a noisy audio breadboard to get FCC attention.
Title: Re: R.F. Interference....Slight Return
Post by: Big Monk on March 16, 2021, 06:38:22 PM
I値l try to run through what I experienced better in a bit when the kiddos go to bed. I値l annotate my picture as well.

For now, I have Leprechaun traps to set...This is our year. When we catch him, we shall give no quarter.

My son has already promised a prolonged interrogation.
Title: Re: R.F. Interference....Slight Return
Post by: Rob Strand on March 16, 2021, 06:51:44 PM
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.

When the RF interference is strong you might find you need a low cut-off on the RC filter.
Low cut-off means a larger cap and/or a large resistor.   A large cap will load the pickup.
A large resistor will increase noise.  I've helped people in the US in the past with RF
issues and the RC values were on the fringe of becoming an issue.    For the resistor
start with 4k7 and for the cap 100pF.    If that doesn't work try 10k or 22k for the resistor.
If that doesn't work try the largest resistor and 220pF.   It's undesirable to go higher
on the cap.

If you find something that works see if you can get a solution with parts in the range R = 2k2 to 10k, C = 47pF to 100pF.

Title: Re: R.F. Interference....Slight Return
Post by: Big Monk on March 16, 2021, 08:00:01 PM
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.

When the RF interference is strong you might find you need a low cut-off on the RC filter.
Low cut-off means a larger cap and/or a large resistor.   A large cap will load the pickup.
A large resistor will increase noise.  I've helped people in the US in the past with RF
issues and the RC values were on the fringe of becoming an issue.    For the resistor
start with 4k7 and for the cap 100pF.    If that doesn't work try 10k or 22k for the resistor.
If that doesn't work try the largest resistor and 220pF.   It's undesirable to go higher
on the cap.

If you find something that works see if you can get a solution with parts in the range R = 2k2 to 10k, C = 47pF to 100pF.

Will try this before doing anything drastic like starting over.


(https://i.postimg.cc/MXVyFnGZ/8301-E373-E255-4-CE3-85-C6-789-AA3085-B2-A.jpg) (https://postimg.cc/MXVyFnGZ)

Let me clarify a few things about the annotated picture above:

A.) The power section is here. Input is through the DC jack into a simple power supply filter comprised of an RC filter with 820 ohm R and 100 uf C, along with a 0.047 uf film cap parallel with the 100 uf.

B.) These are my test points. I have 3 red jacks for checking collector voltages, or any important values for that matter, externally. There is a test point to ground as well.

C.) My input is a box jack. Chassis connections is made through this jack from the metal lip on the sleeve. I have a ground wire from sleeve to ground rail on breadboard as well. Shield wire is connected with shield connected to sleeve and inside conductor connected to tip. This goes to the switch with no shield connection. No shield connection leaves the switch but then shield is connected to ground rail on breadboard.

D.) Here is my switching and LED. Pretty standard true bypass wiring with LED switching. I have long leads for swapping leads for PNP circuits.

E.) Output shield wiring is same as input. This jack is isolated from enclosure with a ground wire from sleeve to ground rail on breadboard.

Anything jumping out to anyone on the basic I/O, power, switching, LED setup?
Title: Re: R.F. Interference....Slight Return
Post by: Rob Strand on March 17, 2021, 01:43:18 AM
Quote
Anything jumping out to anyone on the basic I/O, power, switching, LED setup?
It looks pretty good to me.

Something which can help RF is putting the filter resistors at the socket instead of on the PCB.
You can also add a resistor in series with the signal at the output socket; IIRC Cornish does this.
This stops the RF before it gets into the enclosure.  It can also stop RF coupling around the switch.

In the true bypass wiring scheme the resistors at the socket and the resistors at the PCB
aren't quite the same.   In bypass the resistors at the socket will place the resistors in series with
the signal path.   The resistors at the socket can't be more than 1k.   So really, you still need the filter
resistor and cap at the PCB and the 1k are just "additional help".  It might be enough to fix very bad RF
issues.

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.

The thing to keep in perspective is people have no RF issues with much poorer wiring than you.   The thing is though
their environment probably doesn't have strong RF.  If your area has particularly strong RF  then you might need
to go above and beyond the normal defenses and that could mean adding extra parts which are normally not
required.   Back in the days of CB radio people modified their equipment from outside by wrapping cables around
ferrite rods and through ferrite torroids.   They were the extra fixes to cope with the the bad local conditions.
Title: Re: R.F. Interference....Slight Return
Post by: amptramp on March 17, 2021, 07:11:00 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.
Title: Re: R.F. Interference....Slight Return
Post by: Big Monk on March 17, 2021, 07:38:59 AM
Quote
Anything jumping out to anyone on the basic I/O, power, switching, LED setup?
It looks pretty good to me.

Something which can help RF is putting the filter resistors at the socket instead of on the PCB.
You can also add a resistor in series with the signal at the output socket; IIRC Cornish does this.
This stops the RF before it gets into the enclosure.  It can also stop RF coupling around the switch.

In the true bypass wiring scheme the resistors at the socket and the resistors at the PCB
aren't quite the same.   In bypass the resistors at the socket will place the resistors in series with
the signal path.   The resistors at the socket can't be more than 1k.   So really, you still need the filter
resistor and cap at the PCB and the 1k are just "additional help".  It might be enough to fix very bad RF
issues.

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.

The thing to keep in perspective is people have no RF issues with much poorer wiring than you.   The thing is though
their environment probably doesn't have strong RF.  If your area has particularly strong RF  then you might need
to go above and beyond the normal defenses and that could mean adding extra parts which are normally not
required.   Back in the days of CB radio people modified their equipment from outside by wrapping cables around
ferrite rods and through ferrite torroids.   They were the extra fixes to cope with the the bad local conditions.

When I have some time today, I値l test some of this out and clean up the circuit wiring to have shorter runs, etc. I値l post back my results.

If i am grasping your suggestions properly i'd:

1.) Put the RC Filtering in series with the lead and the tip of the input jack and;
2.) Put a series R in between the lead and tip of the output jack
Title: Re: R.F. Interference....Slight Return
Post by: Big Monk 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!
Title: Re: R.F. Interference....Slight Return
Post by: Big Monk 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.
Title: Re: R.F. Interference....Slight Return
Post by: Big Monk on March 17, 2021, 03:07:56 PM
Something just occurred to me.

I do all my testing on this little guy:

(https://marshalldotcom.blob.core.windows.net/assets/content/uploads/d1f1a3dc-354f-46dd-8961-91dcb6aa8f2a.jpg?20180406135649)

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?
Title: Re: R.F. Interference....Slight Return
Post by: garcho 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
Title: Re: R.F. Interference....Slight Return
Post by: Big Monk 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.
Title: Re: R.F. Interference....Slight Return
Post by: Rob Strand 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).

 
Title: Re: R.F. Interference....Slight Return
Post by: Big Monk 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 I知 getting from RF. I知 just about done assembling my first tube amp in some time and I will table this until I知 finished.