RF noise filtering

[phsyconoodler]

I've got a friend who has an interesting noise problem.His house is near a  power station and has some noise issues when he plays his amps.
  The power in the house has been checked by am electrician and he says it's wired right.
Buzzy single coils,not as bad with humbuckers.
   A friend suggested adding two .1uf/600c caps from the AC/hot and neutral to ground.
Any other ideas?
  Ok,I'm not sure if it's RF or dirty power,but either way,it's nasty.I haven't heard it myself but he says it makes the house useless for rehearsal.He has a Furman conditioner.

[jojokeo]

For RF I use a .01/100v to ground at the input jack's ground for protection. Something else that extra filtering like what's seen used on IEC sockets may be worth a try also? (at Mouser) http://www.corcom.com/PDF/EASEBS.pdf

[phsyconoodler]

Never seen a cap like that on an input.Thanks Jojokeo!
It really filters out RF?

[jojokeo]

I've read as many articles on grounding lately as I could find on the web and from the "good books" available today, including Doug's info on this site. There's a lot to be said regarding grounding and in high gain amps especially, it is even more important for a quiet - non oscillating amp. This was due to my amp called Bumblewatt that I made while the HRM amp was being done by some here. Doug doesn't advocate star grounding while others like Aiken and Merlin discuss using it and/or hybrid versions of buss & star grounding. This can be a hotly debated subject potentially. Anyway, one of the recurring themes suggested is the use of isolated jacks also. I'll post part of Aiken's info here as he explains this and it's relation to eliminating RF.

"Do not use the pot casings as ground points.  Any pot terminals that are grounded should go to that stage local ground point.  Do not ground the input jacks, and be sure to use isolated input jacks.  Run the input jack ground to the local ground of the first stage, which then goes to the star point.
Important note: While the star ground is excellent for eliminating ground loop hum, it is not always the best scheme for preventing radio-frequency interference (RFI).  Fortunately, there is a simple addition to the star ground scheme that will make for a very quiet amplifier with no RFI.  Simply add a 0.01uF capacitor from the chassis to the ground lug of the isolated input jack using very short leads.  This will shunt all of the RF "riding" on the shield of the cord straight to the chassis ground before it can get into the amplifier and cause problems.   Any kind of ground lug can be used for the chassis connection of the capacitor.  You may be able to find a solder lug that slips over the shaft of the isolated input jack for a convenient ground lug.  Use of an internal-toothed lockwasher is recommended for these types of connections to insure a good "bite" into the chassis for a good ground.
You can experiment with variations on this system.  All the above suggestions are not always necessary, especially if you are willing to put up with some residual hum.  Star grounding is not always necessary, and some very quiet amplifiers have been built using buss grounds or other grounding schemes. A little planning in the early stages can save you a lot of aggravation in trying to eliminate the hum after the amp is built."

*If you notice in my picture, my grounded pots went directly to the the chassis ground point (where they serve as a signal shield) but not the star ground which is back at the resivoir filter and output stage filter caps. Also, I didn't ground my signal ground to this. The signal ground was kept seperate and went to each stage's ground points of their respective filter cap/cathode grounds of their respective stages. The result of all this is a very quiet high gain amp w/out any RF interference or parasitic oscillations. Bottom line is it works for me. Hope this helps, Keo

[dennyg]

Keo - i found this old post about RF filtering using a .01cap from input jack, including a pic you posted from one of your builds.  I don't have RF issues but on a mission to minimize noise/oscillations in high gain builds, trying every new trick i can find.  Question: I'm using a star/bus scheme, with only one ground connection from the board to chassis via stage 1 cathode. The isolated input jack is also grounded at that same point.  Would I replace the ground wire from input jack to chassis with the cap? i.e.  the only ground from input will be via the cap? 
Thanks - Denny

[J Rindt]

How is it possible to hear RF in a guitar amp.?
Take AM for example.....doesn't the carrier frequency have to be demodulated (or whatever it is called) before you can actually hear the Audio.?
I have always read that is what those (typically) 68k resistors are for at the first grid of V1. But i have always wondered.....how can you hear the RF.?
Thank You

[jjasilli]

I'd consider the issue of ambient noise produced within the home.  I traced a bad noise issue to the use of a dimmer SW > incandescent bulbs in a ceiling fan.  Ironically, operating the ceiling fan had no effect.  Fluorescent bulbs are another usual suspect.

[shooter]

how can you hear the RF.?

You can't hear RF, but you can hear it's effects, causing a tube to become erratic, harmonics of the fundamental "noise", causing the small input audio to get "lost in the noise"

[J Rindt]

how can you hear the RF.?

You can't hear RF, but you can hear it's effects, causing a tube to become erratic, harmonics of the fundamental "noise", causing the small input audio to get "lost in the noise"

I understand what you are saying, and that certainly makes sense.
Wish i had a link, but..... several times over the years i have read posts with a title something to the effect of  "My Amp Is A Radio".
I have always wondered how those guys could be gearing Music/Voice from a radio through their amp.
Thanks

[shooter]

"My Amp Is A Radio".

Yup, built one myself, not on purpose! The funny thing, my son called from 200miles away wanting his amp fixed cause he was picking up a radio station.  we compared notes, Isolated the station to a Christian station about 1/2way 'tween us!  Just guessing, but google up RF inductive coupling, RF jamming, RF interference in audio, you should find the "whys n hows" in some engineering/college threads.
typically the fix can be found in poor grounding, bad shielding. 

[HotBluePlates]

... several times over the years i have read posts with a title something to the effect of  "My Amp Is A Radio".
I have always wondered how those guys could be gearing Music/Voice from a radio through their amp. ...

A.M. Diode Detector (or a Crystal Radio).

If you have a large amplitude-modulated R.F. field, a tube's grid can look like a diode.  Specifically, if you drive the grid (usually of a preamp voltage amplifier) in the positive direction beyond the value of the bias, the grid goes from looking like an infinite input impedance to some low impedance (it draws grid current).

So a strong A.M. signal could make the preamp tube act like a diode detector for an A.M./Crystal radio, and demodulate the audio. The audio gets amplified by the rest of the guitar amp.  An A.M. radio does the exact same thing, but usually does some amplification at a frequency well above the audio range to improve the ability to select one station for amplification/listening.

Like the simple crystal radio, only the strongest signals around the guitar amp pose a risk of being demodulated/amplified.

[J Rindt]

... several times over the years i have read posts with a title something to the effect of  "My Amp Is A Radio".
I have always wondered how those guys could be gearing Music/Voice from a radio through their amp. ...

A.M. Diode Detector (or a Crystal Radio).

If you have a large amplitude-modulated R.F. field, a tube's grid can look like a diode.  Specifically, if you drive the grid (usually of a preamp voltage amplifier) in the positive direction beyond the value of the bias, the grid goes from looking like an infinite input impedance to some low impedance (it draws grid current).

So a strong A.M. signal could make the preamp tube act like a diode detector for an A.M./Crystal radio, and demodulate the audio. The audio gets amplified by the rest of the guitar amp.  An A.M. radio does the exact same thing, but usually does some amplification at a frequency well above the audio range to improve the ability to select one station for amplification/listening.

Like the simple crystal radio, only the strongest signals around the guitar amp pose a risk of being demodulated/amplified.

Per Usual......Great, Thank You.
That explains it.....VERY Interesting Indeed.
thanks again...I Appreciate It

[scstill]

For RF I use a .01/100v to ground at the input jack's ground for protection.

This worked for me today I put this capacitor across the 1M resistor at the input jack. Squeal gone.

[shooter]

got an amp in once where the owner said "This thing keeps picking up a radio station, It's kinda weird, it's a Christian station like 100 miles away"
after I asked if he's sure, since, well.......

can't find the module I've used, most audio amps have a "filter" at the input, this is a typical example.  The one I've used was a "double CRC" type.




https://el34world.com/charts/Schematics/files/Altec_lansing/Altec_lansing_1568a.pdf

[stratomaster]

For RF I use a .01/100v to ground at the input jack's ground for protection.

This worked for me today I put this capacitor across the 1M resistor at the input jack. Squeal gone.

I think you misunderstood what was happening at the input. What you've done just creates a low pass filter with a cutoff in the high mid frequency range. 

The 0.01μF cap in question ties an isolated jack ground sleeve to chassis ground.

[scstill]

I think you misunderstood what was happening at the input. What you've done just creates a low pass filter with a cutoff in the high mid frequency range.  The 0.01μF cap in question ties an isolated jack ground sleeve to chassis ground.

Sorry I should have mentioned my issue which was squeal from a pentode channel not dirty AC.
I used this thread as inspiration to fix and wanted to comment as such.
This approach seemed to fix it, I haven't noticed any effect on the input signal but will check.

If there is suggested better approach to the squeal could you respond in the attached link? Thank You
https://el34world.com/Forum/index.php?topic=32660.msg362484#msg362484

BTW - was thinking of using isolated jack but since this and the shield (see topic) mostly fixed my 2 issues I did not