Isolation and Grounding

 

"Having a quiet guitar rig brings the magic.  Having a noisy one is a pain in the amp. "  (sigh)

Jody "KingSnake" Page (PedalSnake inventor)


The helpful info on this page applies to all guitar rigs, whether you use PedalSnake or not.  For those who may encounter a problem, we include tips on how to isolate and kill noise in PedalSnake rigs too.

The three examples below are not the only ones we could show.  But if you understand these three, then you can figure out most any isolation or ground loop hum problem.

 

Isolating Digital Noise

Isolating Power Chains

Isolating Stereo Amps

 



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Isolating Digital Noise

Digital pedals produce some of the best effects around, especially in time-based modulation type effects.  But when not managed properly, the high speed switching of digital data within a digital pedal can cause a special kind of noise.  See Digital Noise at Noise: Types and Causes.  Most all digital pedals do a good job of filtering noise out of their audio output signal.  But they don't always do a good job of keeping it out of the power input line.
When a digital pedal with poor noise filtering is put on a power chain, the noise escapes into the chain.  Any analog pedals on the chain can become infected. 

Analog pedals have no need to filter digital noise.  And since audio signal ground and power ground are the same, the noise on the power ground enters the audio signal, and continues to the amp input. 

BAM...you hear digital noise, usually as a high pitched whine.
Fortunately, this is easily fixed without breaking the bank.

We are often told the only way to fix this is to rush out and buy an expensive power supply with multiple isolated outputs.  Yes, that will fix it, but it is also expensive. 

Cost:  $150+

All that is needed is to isolate the offending digital pedal on its own isolated power supply. 

Cost:  $20
 
NOTE  With PedalSnake, when isolating power, use two separate MF1-H Single P-Line Pigtails, or MF2-I Dual Isolated P-Line PIgtails on the white 5wire channel.  MF2 Dual P-Line can come in very handy to save channels, but with its shared ground wire, it will not support isolation of two power supplies. 
 

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Isolating Power Chains

Slightly different grounds can exist in devices, even if they are plugged into the same outlet.  This is worse when one or more of the devices draws a lot of current from the wall.  Tube amps draw a lot of current.  This current flows in the windings of their power transformer, which can induce small voltages into the grounded metal chassis. 

These different induced ground potentials can exist in many ways, even on the same chassis.  When these different grounds are connected, either thru audio or power cables, hum will result unless a way is found to isolate the grounds. 
Because they are the most common offender, we will use two stereo amps as and example.  In the first case, a pedal power chain is the culprit that ties the grounds together.

If the grounds of two stereo amps are tied together by a power chain, and the induced ground voltages are slightly different, 60Hz ground loop current will flow in the grounds of the audio guitar cords.  Hum is the result.
We are often told the only way to fix this is do away with the power chain.  We must rush out and buy an expensive power supply with multiple isolated outputs.  Yes, that will fix it, but it is also expensive. 

Cost:  $150+

All that is needed is to isolate the two power chains on their own separate isolated power supply. 

Cost:  $20

NOTE  With PedalSnake, when isolating power, use two separate MF1-H Single P-Line Pigtails, or MF2-I Dual Isolated P-Line PIgtails on the white 5wire channel.  MF2 Dual P-Line can come in very handy to save channels, but with its shared ground wire, it will not support isolation of two power supplies. 


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Isolating Stereo Amps

The analysis here is the same as for Power Chains (above).  Slighly different grounds can exist in devices, even if they are plugged into the same outlet.  This is worse when one or more of the devices draws a lot of current from the wall.  Tube amps draw a lot of current.  This current flows in the windings of their power transformer, which can induce small voltages into the grounded metal chassis. 
If the grounds of two stereo amps are tied together by a stereo pedal, and the ground voltages are slightly different, 60Hz ground loop current can flow between the amps in the ground wire of the audio guitar cords.  Hum again is the result.

With a stereo pedal, the grounds are being tied together by the two guitar cords going to each amp's input.  So ground currents flow in the audio signal ground, causing hum.
The only way to break this audio ground loop is too insert an audio isolation transformer on one of the lines. 

Audio isolation transformers can be found online.  Ebtech makes some good ones.

Once one audio line is isolated, the grounds are separate, and no more ground currents or hum.
 
NOTE  When isolating audio with PedalSnake, you must keep the grounds of the cables going to the two amps separate.  So if the transformer is on the pedalboard, use two separate RS1 Single G-Line Pigtails to go from the board to the two amps.  The shared ground wire of an RS2 Dual G-Line would only serve to tie the two grounds back together after the isolation transformer. 
   


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