ground loop isolator and band aid fixes...

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

pucho812

Well-known member
Joined
Oct 4, 2004
Messages
14,830
Location
third stone from the sun
Was reading up on this after a studio visit yesterday. A friend was "recording" but the electrical was so bad that any guitar amp with almost every guitar they had was buzzing  to the point it was louder then any guitar audio. This was with any guitar and pick up combo of active or passive, Humbucker or single coil except for one Strat with noiseless pickups.    The buzz would change volume based upon where you positioned yourself with the guitar in the room and the buzz changed when the el cheapo dimmers were used.  The amp when not connected to a guitar was quiet as a church mouse.
Aside from the obvious of the studio needs to be electrically wired correctly, no bootstrapped grounds, Iso ground outlets, etc/  What are some good ways to band aid the situation to work.  Obviously the guitars would need better shielding internally and should have it.  Obviously using a 3 prong to 2 prong plug is not only dangerous, it is a big no no for many reasons.
Do things like the attached below really work?
The diodes are 35A which seems high except they are on purpose to allow the breaker to do it's job.  The cap is a .01uF and the fuse is optional.


 

Attachments

  • Novacek301-4.jpg
    Novacek301-4.jpg
    16.2 KB · Views: 33
I used the diode trick back in the 70s, but not now.

Do whatever it takes, but please if humans are involved (including musicians) buy a cheap GFCI power drop, to protect the meat puppets from harmful voltages.

JR
 
JohnRoberts said:
I used the diode trick back in the 70s, but not now.

Do whatever it takes, but please if humans are involved (including musicians) buy a cheap GFCI power drop, to protect the meat puppets from harmful voltages.

JR

well my thought is to have a portable  wired outlet in a box  for a  band aid situations not a permanent fixture in the walls.  I know there is a lot  internet ideas on this(both way incorrect and correct) and can even get things like a humX box but I figure a DIY solution will do me.  But yes whenever humans are involved exercise care, nuder and spade your guitar players  ;D
 
Kill switch  anything running off SCR dimmers for a start , I have one room with a dimmer switch , two dials , one with a non dimmable CFL , so its always set to full if its on , and another halogen which dims fine .
Anything with a pick up coil or unscreened electronics is noisey as hell  ,like you describe at a similar level to the sound output in close proximity to the CFL , its makes the entire room totally incompatible with almost any kind of low level amplification .The halogen lamp is less troublesome , some modern Cfl are dimmable , these will most likely make a bad situation worse ,

Maybe suggest trying only incandesent lamps without dimmers in the room your guitar player is working in , it might involve keeping the usual semi pro studio 'mood' lighting panel fully off ,and just running a few table lamps directly from the sockets ,
In the studio I worked in there was the biggest lighting panel I ever saw ,no dimmers whatsoever ,just a bank of 50 or so switches controling many pairs or clusters of colours that could be mixed , brightness or dim wasnt controlled by SCR's ,but by number of switches turned on .

In a live situation where you might have 10's of thousands of watts of dimmable lighting  racks  a three phase supply  is used , typically you have sound on one phase , lighting on another and anything else electrical such as bar equipment on the third phase .
 
luckily it's not my guitar player or my studio. I have no involvement here other then I did a quick visit to a spot a friend is working at. The room is small.  What was interesting was even with lights off buzz was still bad...
 
Its a much more hostile environment nowadays with switchmode doing the rounds ,your highly likely to be seeing an acumulated RF trash on the wires and in the room itself ,
If your friends have no option and want to try to records there ,keep powering  stuff down until the noise goes away , that might just not be feasible at all depending on the situation . Poor grounding as well as  above scenarios and your going to be totally drowned in a sea of noise , maybe consider a change of location
 
One way that could work is , plug the guitar into a battery powered active di , put him somewhere theres less induced noise then run a line from the di box to the amp back in the room . Di is balanced output but you need to unbalance at the amp end , you'll want a proper transformer isolated di ,then connect pin 2 to tip pin 3 to slieve , allow the ground/screen only on the DI end of the cable . If you can find a quiet spot it should work .
 
Tubetec said:
Di is balanced output but you need to unbalance at the amp end

DI produces a balanced Microphone signal output.  Lower voltage and Lower impedance than instrumentl signal
The guitar sound will change a lot and most guitar players are not pleased with the results, I can totally understand why.

If you want to go a similar route but with better results,
you can use this unit:

https://www.radialeng.com/product/sgi

sgi-thumb-768x765.png




You can also DIY something similar.

The transmiter box (Active), has an Hi-Input impedance buffer, and converters the signal into balanced line level

The receiver Box is Passive, and it's the same as a Reamp Box, receives Balanced Live level and converts it to Hi-Z intrument level

The sound will also be different than connecting the guitar directly to the amplifier, but it's a better solution than sending to the amplifier microphone signal

 
You can also DIY a similar device to an Hum-x unit,
check this link:

http://www.epanorama.net/newepa/2010/06/22/secrets-of-hum-elimination-plug/

earth-f4.gif


But these devices and the circuit you showed are only to address ground loops problems/noise.

By your description it seems the problems in that studio are more than ground loops, and are probably more related to electro-magnetic and RF interference in the electric guitar circuit and cables, the Hi-Z signal basically.

Good Guitar Shielding can help a lot, but thats a shield for interference, the best thing is not having any interference to be shielded at all.
So the sources of interference should be the first things to address




 
This Box is also quite usefull to have, it's an audio isolation box, it already helped me out in a number of ground loop noisy situations with guitar amplifiers.

https://www.thomann.de/pt/art_dti.htm

ART DTI
Dual Transformer / Isolater

    Hum Eliminator
    Frequency response 10 Hz to 50 kHz
    THD: 0.01%
    2 Channels
    Inputs and unbalanced XLR balanced, TRS, RCA
    Output as balanced XLR, jack unbalanced, RCA

10085520_800.jpg
 
I had also the same/similar problems in different places I recorded.

I actually have a past thread around here describing a studio/wharehouse belonging to an Indie label I work with were everything audio related has induced noise. The wharehouse is located in an old industrial area, with the railroad track next to it.

Guitar amps, microphones, DI boxes, anything you record there has noise, mostly 10khz.
I was never able to reduce the noise na matter what I tried.
 
pucho812 said:
what would you recommend sir John?
Besides what I already posted?

I am sure I posted about this back when I researched it but I developed an approach around a GFCI power drop with a ground lift switch.  Instead of completely opening the safety ground path I kept a capacitor in path. From memory (which even I don't trust) I think the series cap value I computed to still trip the GFCI (@ 6 mA with 120VAC) was something like 0.16uF... 

Of course this is not remotely UL approved so don't tell your lawyer.

The GFCI circuit will protect meat puppets even with an open circuit ground path. The 0.16uF*** looks like a low Z ground for shunting hum noise from cables and product chassis.

If I was a younger, wealthier man I would be selling these, but the market that would appreciate this is too small to justify the several $10k of UL filing expense and verbal arm wrestling.

While I will deny any knowledge if asked,  you could drop a $15 GFCI outlet into a junction box with or without the cap and ground lift switch. I added my cap and switch to a commercial GFCI power drop.

I even had an old friend of mine who is a respected guitar amp designer (respected by me), test out the trick ground lift on his personal rig... He confirmed that it worked as expected...

In my crystal ball there is no need for the lift switch, just leave the 0.16uF cap in path 24x7.

JR

*** to keep UL happy the cap needs to be rated as an X cap, but even if it shorts it is just providing a ground path, so whatever..
 
> The buzz would change volume based upon where you positioned yourself with the guitar in the room

Obviously the air in that room is full of crap. Ground-break can't help. Walk around until the buzz is worst. Whatever you find there needs to be killed.
 
I noticed the guitar shielding looked like copper foil. Does ferrous foil affect the pickup magnetics? Wouldn’t it be better to use ferrous foil?
 
While I didn't specify, the 0.16uF cap still in path with my GFCI ground lift, is low enough impedance to sink shield noise, while high enough to break any ground loop.

JR
 
JohnRoberts said:
While I didn't specify, the 0.16uF cap still in path with my GFCI ground lift, is low enough impedance to sink shield noise, while high enough to break any ground loop.

JR

So searching found a thread with your gfci box. I should  make one for the emergency kit...
 
Back
Top