GROUND LOOPS, SNAPS ,CRACKLES and POPS!!

		   by Michael Gore  copyright 1994

I've been an Audio Technician since 1972 when I worked in  
major recording studios (CBS Records, Fantasy Records) and 
since going independent as an Audio Tech in 1982 I've set up 
loads of small, intermediate, and large studios.   There are 
more than a few things I've learned over the years, but one 
of the most important is How to Troubleshoot a system, what 
to look for, some basic tests even the non-technical can do 
for themselves. And with just a simple approach to trouble-
shooting your own system, you'll be able to save money by 
fixing the problem  yourself, or at least you'll know when 
to call in outside help.  In this article I'm going to try 
and give you an approach to troubleshooting your own studio 
that will isolate the faulty component or equipment.  

First off, one of the most important things to know is what a 
professional studio control room should sound like, because that's 
your goal: to sound as good as you can.  What comes out of any top 
studio's monitor speakers, is well, nothing... that is when there's 
no music, there is no noise.  This seems obvious, but time and time 
again I go into project studios where there are buzzes and small 
audible pops and  loads of hiss and hums coming out of the monitors. 
And too often the person who runs the place thinks these sounds are 
"normal", and that they have to just live with them.... NOT SO!!

  If you've set your system up correctly, you should be able to turn 
your monitors up to a comfortable listing level, and hear no hiss, 
no hums and a good clean nothing.  If you turn your system way way up, 
all you should hear is a nice clean hiss way in the background, with 
no hums, no squeals no buzzes.

Getting here, to the quiet studio, isn't hard.  This is how you begin 
to trace those buzzes, hums and noise, and to eliminate them if possible...

	First off, you've got to have a quiet power amp, and luckily almost 
all of them are very quiet thesedays.  You can test this yourself, by first 
turning OFF the amp, then removing the Input connections, then turning the 
amp back ON, and slowly turning up the volume.  All you should hear is hiss, 
and this you should only hear when the amp is turned way up.  If you hear 
Buzzes, pops or your local radio station, try turning OFF the amp then 
installing shorted Input connectors (that is the connector's "Hot" and 
"Ground" points are connected together (shorted)... so there is no possible 
Input Signal).  If you don't hear a nice clean hiss, them you have a bad 
Power amp, so go get it fixed.

	So now you've got a clean Power Amp.  It's quiet.  The next thing is 
to turn it OFF and hook up the output from your console, then turn it On and 
slowly bring up the levels on the Power Amp to reasonable volume:  have the 
Monitor Output and all the faders of the console down, and all the channels OFF.  
Again it should be just about as quiet as the Power amp alone( a little more 
hiss is to be expected, but it shouldn't be much).  Then bring up the console's 
Monitor level control to "normal" (which in almost all boards is about 2 o'clock 
or 3/4 of the way up).  The system still should be quiet, no hums, no clicks, 
no buzzes.  

	OK, so you don't have a quiet system, what should you do?  Note that 
when I wanted you to check out your Power Amp, we ISOLATED it from any other 
cause of noise.  We listened only to it, nothing else.  We made sure that not 
even the wires of the Input cords were connected, since those wires themselves 
could have caused a "Ground Loop", which would have caused hum in our system.  
With a few slight modifications, we need to do this every step of the way, 
isolate pieces of the system, and determine what pieces are causing hum or 
buzzes, and what are clean.

	So say that when the console is connected to the power amp, you have 
a hum, even when you turn down the console's Monitor output.  This is most 
likely a Ground Loop, which means that there is more than one ground (which 
is your system's "Zero Volt" reference).  Once there is more than one system 
ground, if there is even a very, very  tiny difference in Voltage between them, 
that small difference will be amplified just as if it were any other normal 
audio signal.  After all, the heart of the matter is that you want all signals 
"Not equal to Zero Volts" to be amplified! So one piece  of gear's Zero had 
better exactly match each and every other Zero in your entire system.  If it 
doesn't, that difference ends up as a 60 hertz hum or buzz.

	So next we'll have to determine if the console, by itself, 
is quiet.  And just as we did with the Power Amp, we'll have to isolate 
the console from all other systems, except for the Power Amp.  So you 
have to disconnect each and every piece of gear plugged into the console.  
Out go all those Synth connectors, reverb and effect connectors, what 
you want is nothing connected to your console except the Power Amp. 
Yes you'll need to dis-connect everything.  Once you've done this, 
and all cables and connectors are removed from the console (except 
the feeds to your Power Amp), you should have a quiet system once again.  
If you don't, try running a Ground wire (12 gauge Green multi-strand 
wire... you can get this at any home improvement hardware store) from 
the Chassis of the console to the Chassis of the Power amp. Strip off 
 1/2 inch of the outer cover on both ends so bare wire is exposed, and 
find a screw on the console to temporarily hold one end of the wire, 
then holding the cover of the wire, touch the chassis of the Power Amp 
(don't have the volume up very high!)  This will either bring up the 
hum (so you don't want the wire connected at all) or it will bring 
down the Hum (then you'll want to crimp "Spade Lugs" on the ends of 
the wire, and find a screw you can use to clamp each end tightly to 
each chassis, never never just wrap the bare end wire around a screw 
and leave it that way!  Always use Spade Lugs: first you Crimp and 
then Solder... ask at the hardware store if you don't know how to 
crimp a Spade Lug... it's easy, and you already know how to solder a wire) 

 
   If you've still got a hum, make sure that the connectors are wired 
correctly.  Finally, if nothing helps, you'll need to try installing a 
pair of good quality audio transformers between the console and the Power 
amp.  A transformer will Isolate the equipment from each other (no ground 
wire between them), and thus there cannot be a ground loop.  If you've 
still a hum, even after installing a transformer between the Console's 
Monitor Output and the Power Amp's input, well then the odds are pretty 
high that the console itself is causing the hum.  
Usually that mean's the Console's Power Supply is faulty, and isn't 
putting out clean DC voltages, or that the Console itself is somehow 
picking up a massive magnetic field nearby, or there might be an internal 
chip that's gone bad...  I had one client who called me after he built 
and did his own wiring of his studio, complaining of a hum in the system.  
I did ALL of the above, and after testing the Console's Power Supply, 
I could only surmise that there was a magnetic field of some very large 
strength nearby.  Then I physically turned the console 90 degrees to the 
side, and Volia! the hum went away.  It turned out that there were the 
main AC supply cables to 2 TV stations  running exactly parallel to and 
at the same height  my client had placed his console (it was a basement 
studio in an old office building).  The console's ground buss (the Zero 
reference wire) running the length of the console was too thin, and the 
ground connections inside the console were not solid, and they allowed 
a bit of induced hum into the system.  Turning the console would work or 
redoing the internal grounding of the console would work.  

   Now if bringing up faders on your console brings up a hum, you're 
better off, since you can just bring up each fader until you find the 
culprit, then remove all cables to and from that one piece of gear.  
If the system returns to a quiet state, then you'll need to try a ground 
wire as we discussed above, once you re-connect the offending piece of 
equipment back to the console.  Next you'll have to try and use a transformer, 
to make sure that the gear is working OK, and there is indeed a grounding 
problem.  And remember, you need to TOTALLY ISOLATE it, you can't just 
isolate the Outputs and leave the Inputs connected, grounds are in both 
Inputs and Outputs, and even in MIDI connectors too!  You have to 
disconnect every connection, then you  can try a transformer on just 
the Output cables to the console.  If the gear is now quiet, try 
connecting the Output directly into the Console.  If it now hums, 
then try the Ground Wire.  If it still hums, but didn't when the 
transformer was used, then check your audio connectors, you might 
have mis-wired something.  If all else fails, then you'll have to 
get transformers for this piece of gear.  One thing to try is to 
physically move remove the piece of gear causing the hum from any 
rack system you might have, since the rack rails are connected to 
the chassis of other equipment, there is a chance that moving the 
gear might solve the problem.



	Well after reading all of this, you get the idea that you 
have to isolate each piece of equipment from everything else, connecting 
it all back together one piece at a time.  We first did the Power Amp.  
Next the console.  If the system is clean, then we'll connect one synth 
or processor and check for hums and buzzes.  If it causes a hum, you'll 
follow the basic steps above, and trace the problem.  Some pieces of gear 
just damn well causes hum from faulty engineering and design, and you'll 
have to isolate these via audio transformers.  But most will connect up clean.  
You have to check each time you add a piece of equipment: does it cause a hum 
in the system, or are there new pops or static?  

If so try a ground wire between chassis, a transformer and so on.  
One thing more: Move those dang AC Plug-In Power Cubes aka "Wall-Warts"
as far away from the console, power amp, and ANY audio wiring.  
Those things are the cause of most of the hums I get called in to fix.  
They emit large magnetic fields which are easily picked up, 
so move them  away from your system! 
 
   In a large top-of-the-line studio, we'll go as far as isolating 
each piece of gear from the AC plug ground and run a separate chassis 
ground wire back to the main studio ground (we call this "Technical Earth"), 
then we'll connect this "Tech Earth" back to the main AC ground, 
and/or a large copper rod driven 18 feet into the ground.  

Thus every piece of gear still has AC fault protection, but no grounds 
are tied together. This kind of system is what's known as a STAR-GROUND.   
This is a time consuming and complex wiring scheme, but is always fool-proof... 
well almost....  even the best designs sometimes fail.

Also in a 'Star-Ground" system, the audio ground wires are never connected to
any 2 pieces of gear... each ground is connected to the output only, and 
with the exception of all Mic Cables and Mic wiring to the console, Audio
grounds are not connected between pieces of gear..... this is AUDIO GROUND,
not AC Ground.... only the audio ground wire is lifted.

This prevents (in a perfect 'Star-Ground') creating 2 or more paths of
ground between pieces of gear.... since the audio cable never connects 
two Audio grounds together, the only common Audio ground will be the 
very thick 'Star-ground' wire which connects all Audio grounds together
at one place only. 

  You may find some piece of gear that just requires audio transformers 
to eliminate ground loops.  But you'll find that  with most of today's 
equipment, you really don't have to go as far as all this, and with a 
few hours of patient troubleshooting, you'll be able to make your 
project studio much quieter.


NEVER cut or lift the 3rd grounding prong from ANY AC cable!!

NEVER remove chassis ground - this is for protection against electrocution!!!

A "Star-ground" set-up should never leave any piece of gear ungrounded to 
AC ground.  Each piece of gear MUST be grounded for safety.


 
   Now here are a couple of trade secrets...the Ultra-Secret 
"Audio-technician Guild" will come after me for telling you this stuff!!

#1	All consoles want to have their Monitor Volume controls at about 
the 1 or 2 O'clock point.  That's where you get the best signal-to-noise 
levels, which means quieter monitoring.  So play a CD or some music through 
your mixer, set the faders so your meters read normal levels (for VU Meters 
this means peaks of about +2 VU), and turn the Monitor Pot to the 1 o'clock 
position, and turn DOWN the Power Amp levels until the music is at a "normal" 
listening level.  That's the level you want from your power amp.  1 o'clock, 
normal, 4o'clock LOUD!  If you have your Power Amp turned way up, like most 
small studios do, all you're going to do is amplify "normal" hiss from the 
console.  Remember that everything has some noise, so if you turn your power 
amp all the way up, even the best of consoles will sound noisy, even though 
the reality is that the system is very quiet!!  If your Power Amp doesn't 
have level controls, have your local tech build some for you.

#2	Move those dang AC Plug-In Power Cubes aka "Wall-Warts" as far away 
from the console, power amp, and ANY audio wiring.  
Those things are the cause of most of the hums I get called in to fix.  
They emit large magnetic fields which are easily picked up, so move them 
away from your system.  One client extended the wires from the transformers 
to the equipment, and moved them 6 feet away from any audio cable ..
And most of her irritating hums vanished.

#3	If you have a buzz that seems to grow slowly in volume then slowly 
diminish, the odds are that you're picking up the 60 hertz signal from your 
local TV station.  Sorry, but you'll have to get a good technician, and even 
then you might just have located your studio where one shouldn't be.  If you 
have a buzz that seems to come for only short pulses, always at a constant 
level, then it could be a pulse riding in on your AC lines, and this is again 
very difficult to fix.  Try to see if it might be caused by lamp dimmers 
somewhere in the house, a bad florescent lamp or that old 'fridge turning 
on and off.  If the buzz more or less comes on and stays there, try and 
document what time of day it happens... I once traced such a buzz 
down to a large Neon "Safeway" sign a block away, turning on each evening.   
I was able to "Neon-proof" that system, but you can sometimes get the 
store owner to fix the problem sign.  And sometimes just knowing why things 
happens makes them less irritant.

#4	Computer monitors are notorious for causing hums, and you can 
easily trace this just by turning on and off the monitor of your computer.  
If you get a buzz or hum when its on, only changing the position and/or 
increasing its' distance from the console will help.

#5	When you stack various pieces of equipment on top of one another, 
you might find that one piece of gear has it's internal AC power transformer 
in a spot that makes the equipment just above or below it have an audible hum.  
Always try turning off pieces of equipment around any gear that seems to have 
a hum when you can't eliminate the hum with transformers.  Once you find the 
offending unit, just move it to another spot, and try it again.

#6	Get two good audio transformers and build yourself an isolation box.  
There are times that nothing but transformers will eliminate hums, and if 
you've got friends and clients bringing in their own equipment, you can 
save hours of frustrating troubleshooting by just using transformers if 
their gear causes a hum.

#7	 Always match levels and impedances.  Microphone inputs are a poor 
place to put line level signals, but lots of studios try.  If you must use 
your mic inputs for non-mic signals, either use a "Matching Transformer" 
which not only isolates the equipment, but matches the levels as well, or 
have your tech build you a "pad" which will reduce the level from Line  
down to Mic level.  I just converted 18 Mic inputs of a console for line 
level use, making all the changes in each module.  That way this client 
could have two line inputs for most of his console modules, and still 
keep a few unconverted modules around as normal Mic inputs. 

 Remember that the impedance of a mic is about 200 ohms (very low) and 
the impedance of most Mic Pre-amplifiers is about 1,500 ohms (this makes 
for lower noise in Mic Pre-amp designs, which we'll talk about in another 
article).  But most of your synths and equipment want to feed their 
signals into 10,000 ohms resistance (known as "High Impedance").  
Some equipment can feed low impedances, and some equipment can't. 
You end up by getting more noise and distortion than you should if you 
connect gear that can't work with vastly incorrect impedances...  Oh, 
don't forget that most mic inputs also have an output... 48 volts phantom 
voltage to drive condenser mics! Very bad for most anything but a MIC! 
Make sure that you never have phantom power ON if you have to connect 
synths into mic inputs!  


#8  You'll find that your system will normally be in it's quietest 
state when everything is powered up.  It isn't fair to have some 
things turned on and others off, as impedances change when power is 
turned on to a piece of gear.  So almost always have everything "On", 
even if you're not using it all.

#9   Try and "hit" the Input of effects units with a good strong signal, 
and reduce the Effect's output level control a bit.  Lots of reverbs and 
delays have background noise, and you'll help reduce this by turning the 
Output down.   Also don't use lots of compression unless you need to, 
compression will lower the signal-to-noise ratio of that track, and unless 
you also use a noise gate along with your compressor, you'll be adding 
unwanted noise.   

#10	Less is More.  Try using good recording technique rather than loads 
of effects on your tracks.  It's better to have a poor recording of a killer 
performance, than a great recording of a dull boring performance.  

Everyone still buys CDs for the music, not the noise levels.

  

That means the chassis of each piece of gear is connected to a good AC ground.  
This is so that if there is a fault in one piece of gear, you, the user 
cannot be the "ground" for AC current.   That 'third prong' on your AC cable 
connects the chassis directly to AC ground, and once you use an adapter you must 
be sure that there is a ground wire between that gear's chassis and good 
AC ground.  Never remove chassis ground protection!!

	In major studios we use a system called a Star Ground.  Then we'll 
make sure that there are no cross grounds in the audio wiring, as well as 
in the AC cables.  Everything is still connected to AC ground via good 
individual ground wires.  This eliminates almost all ground loops, and 
still insures a safe system.  Plus it makes sure that all "Zero Volt 
References" can stay exactly the same.  We never remove grounding protection.

	In a home or project studio, this same attention to system grounding 
is important.  You've got to insure not only that you system is quiet, but 
that it's safe too.  So make sure that there is always a ground path for 
each piece of gear via the AC 3rd prong ground.  

Never eliminate a ground!!! 

Most modern equipment, there is absolutely no reason to lift the third 
prong of the AC cable, and you should NOT do it in any case.  

	Finally, don't over burden your AC wiring.  Your house wiring is 
meant to supply normal household currents, and isn't designed to be at 
maximum levels for long periods of time.  

Don't have lots of AC outlet strips connected together into one wall outlet.  
Make sure that no AC cable is getting warm when it's used.  

There was one project studio I was in where the guy had 5 AC strips 
daisy-chained into one wall outlet.  That first AC strip wire was 
carrying all the current of the entire chain and was getting hot 
to the touch, making his whole set up a fire hazard.  Don't do this!!

Make SURE that no AC cable is 'frayed' or has lost it's outer cover.  
You should NEVER see the individual AC wires ever!

Lastly - you should NEVER do any AC wiring yourself.  

You MUST hire a licensed contractor or other highly qualified (and legal) 
person to do ANY AC wiring.

Good Quality Audio Transformers are available from:

  Jensen Transformers (some of the best transformers available) (818) 374-5857

	Triad and
	Stancor		both available from Newark Electronics  (many locations)

	there are other manufacturers of Transformers too....	


Transformers		
		

One of the easiest ways to eliminate ground hums is to isolate the offending 
equipment via input and output transformers.  These things do amazing things 
in the audio world and are often contained in the best equipment found in the 
big studios.  Since the whole principal of a transformer works on a transfer 
of only magnetic flux, there is absolutely no physical contact needed between 
two pieces of gear to get an audio signal through. If you need either to quickly 
remove a ground loop caused by poor grounding, or to transform balanced to 
unbalanced signals, grab a transformer.

But transformers aren't perfect.  Expensive transformers are about as near 
perfect as you can get in the audio world, but you pay for the engineering 
and construction quality.  Lesser transformers suffer from their design and 
the way in which they're built, but if you match your requirements to the 
correct transformer, you need not spend an arm and a leg to get what you need...

For the Pro studio, operating at normal +4 levels, you'll have to go for the 
top end of transformers, and I prefer Jensen Transformers (818) 374-5857, 
though there are a few other top manufactures around.  But you're gonna 
pay for top line transformers... the Jensen JT-11P-1 transformer currently 
sells for $63.49 each, then you have to drill out a case for your connectors 
and wire them yourselves.  But here you can put in up to +17 dB before you 
even hit 1% distortion at 20 hertz! Killer performance!!  These are the puppies 
I install when I need top studio performance.

Transformers can do other things besides isolate two pieces of equipment.  
You can use a transformer to step up (or down) signal levels.  So say your 
console is a Pro Standard +4 dB output unit, and you need to drive a 
-10 dB device...  you could turn the input levels of the device way down 
or run the console level way down.  But it's always better to run things 
at their optimum points, so if you could, you would want the console running 
at +4 dB and the next device at -10 normal input fader levels.  A step-down 
transformer can do the trick for you, so everything is right where it should be.  
If you need to hook up both a balanced and unbalanced device to the same 
output, you should isolate the unbalanced gear via a transformer, or else, 
once both are connected to the same point, you've unbalanced the signal to both.  
And if you're working a remote, the only safe way to split mic lines to send 
the same mic signal to more than one mixer is to use a "Splitter Transformer".