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Isolating an audio line connection with two capacitors

Isolating audio ground between devicesGround loop? Switch mode power supply noiseProper power design for a USB deviceGrounding for car stereo adapter PCBMultiple Ground Referenced Sensors on Single Floating SupplyAudio transformer: What to do with an unused winding?Connect Arduino to existing circuit with seperate power supplyAudio Switching Circuit - Ground Loop Noise ProblemLM386 Amplifier not amplifyingAudio Noise with 5532 OpampIsolating audio ground between devices

5

1

$begingroup$

I've looked at several questions, such as:

Isolating audio ground between devices

I want to connect an input and output audio line signal of two different devices. The earth potential of their audio connectors is might be floating, connected to mains earth, or offset by some DC or AC amount, with some resistance and other complications - the usual real-life audio stuff.

Is a simple solution to connect them with two capacitors? The function generator is the line out, and speaker the line in:

^{simulate this circuit – Schematic created using CircuitLab}

I'd rather not use audio transformers if this will do.

Edit - Additional details

• The above values are a bit of a hack. The circuit too, so I'd expect problems like pops on power up at least

audio groundloops

share|improve this question

edited Mar 21 at 3:13

CL22

asked Mar 21 at 2:00

CL22CL22

3,17653161

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Are these balanced or unbalanced inputs and outputs, and will 48V phantom power ever poke its head in?
  $endgroup$
  – ThreePhaseEel
  Mar 21 at 3:04
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  It's just home audio - unbalanced, and no phantom
  $endgroup$
  – CL22
  Mar 21 at 3:12
  

  
  
  
  

add a comment | 

5

1

$begingroup$

I've looked at several questions, such as:

Isolating audio ground between devices

I want to connect an input and output audio line signal of two different devices. The earth potential of their audio connectors is might be floating, connected to mains earth, or offset by some DC or AC amount, with some resistance and other complications - the usual real-life audio stuff.

Is a simple solution to connect them with two capacitors? The function generator is the line out, and speaker the line in:

^{simulate this circuit – Schematic created using CircuitLab}

I'd rather not use audio transformers if this will do.

Edit - Additional details

• The above values are a bit of a hack. The circuit too, so I'd expect problems like pops on power up at least

audio groundloops

share|improve this question

edited Mar 21 at 3:13

CL22

asked Mar 21 at 2:00

CL22CL22

3,17653161

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Are these balanced or unbalanced inputs and outputs, and will 48V phantom power ever poke its head in?
  $endgroup$
  – ThreePhaseEel
  Mar 21 at 3:04
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  It's just home audio - unbalanced, and no phantom
  $endgroup$
  – CL22
  Mar 21 at 3:12
  

  
  
  
  

add a comment | 

$begingroup$

I've looked at several questions, such as:

Isolating audio ground between devices

I want to connect an input and output audio line signal of two different devices. The earth potential of their audio connectors is might be floating, connected to mains earth, or offset by some DC or AC amount, with some resistance and other complications - the usual real-life audio stuff.

Is a simple solution to connect them with two capacitors? The function generator is the line out, and speaker the line in:

^{simulate this circuit – Schematic created using CircuitLab}

I'd rather not use audio transformers if this will do.

Edit - Additional details

• The above values are a bit of a hack. The circuit too, so I'd expect problems like pops on power up at least

audio groundloops

share|improve this question

edited Mar 21 at 3:13

CL22

asked Mar 21 at 2:00

CL22CL22

3,17653161

$endgroup$

share|improve this question

edited Mar 21 at 3:13

CL22

asked Mar 21 at 2:00

CL22CL22

3,17653161

share|improve this question

edited Mar 21 at 3:13

CL22

asked Mar 21 at 2:00

CL22CL22

3,17653161

asked Mar 21 at 2:00

CL22CL22

3,17653161

asked Mar 21 at 2:00

CL22CL22

3,17653161

2 Answers
2

active

oldest

votes

5

$begingroup$

AC mains is a audio frequency so capacitors large enought to pass audio will not effectively block AC hum. use an audio isolating transformer instead.

Small transformers are available for line level signals, and larger ones for loudspeaker signals.

isolation is no needed between a floating and a fixed device unless the floating device must stay floating.

share|improve this answer

edited Mar 21 at 21:50

answered Mar 21 at 3:07

JasenJasen

11.5k1531

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  How do hi-fi separates ensure compatibility?
  $endgroup$
  – CL22
  Mar 21 at 3:14
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  @CL22 -- the thing with "hifi" gear is that it's designed so that everything "floats together" if you will, with ungrounded (Class II, in modern gear) power supplies throughout
  $endgroup$
  – ThreePhaseEel
  Mar 21 at 3:17
  

  
  
  
  

add a comment | 

1

$begingroup$

No, your circuit won't work as expected. The capacitor in the audio ground is connected to the two grounds so if they are at different DC potentials it will simply charge up and stay there at that potential difference, with no current flowing.

Which tells us the real answer; if both audio circuits are grounded and the grounds may be offset, just disconnect the audio return wire with a "ground lift" switch. Note, it is not safe to disconnect an actual circuit/safety ground, just the audio ground connection between the two. So then you just have one wire carrying the signal, with a capacitor in it.

In other words, just avoid a ground loop by not connecting the two grounds together.

share|improve this answer

answered Mar 21 at 7:14

Ian BlandIan Bland

1,9861714

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Joining the two grounds does charge the capacitor to keep it at that potential, leaving no current flowing for DC offsets. I'm sure that that is not an issue. It means both are effectively ground for DC which is what the circuit neeeds
  $endgroup$
  – CL22
  Mar 21 at 18:36
  
  

  
  
  
  

add a comment | 

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5

$begingroup$

AC mains is a audio frequency so capacitors large enought to pass audio will not effectively block AC hum. use an audio isolating transformer instead.

Small transformers are available for line level signals, and larger ones for loudspeaker signals.

isolation is no needed between a floating and a fixed device unless the floating device must stay floating.

share|improve this answer

edited Mar 21 at 21:50

answered Mar 21 at 3:07

JasenJasen

11.5k1531

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  How do hi-fi separates ensure compatibility?
  $endgroup$
  – CL22
  Mar 21 at 3:14
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  @CL22 -- the thing with "hifi" gear is that it's designed so that everything "floats together" if you will, with ungrounded (Class II, in modern gear) power supplies throughout
  $endgroup$
  – ThreePhaseEel
  Mar 21 at 3:17
  

  
  
  
  

add a comment | 

5

$begingroup$

AC mains is a audio frequency so capacitors large enought to pass audio will not effectively block AC hum. use an audio isolating transformer instead.

Small transformers are available for line level signals, and larger ones for loudspeaker signals.

isolation is no needed between a floating and a fixed device unless the floating device must stay floating.

share|improve this answer

edited Mar 21 at 21:50

answered Mar 21 at 3:07

JasenJasen

11.5k1531

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  How do hi-fi separates ensure compatibility?
  $endgroup$
  – CL22
  Mar 21 at 3:14
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  @CL22 -- the thing with "hifi" gear is that it's designed so that everything "floats together" if you will, with ungrounded (Class II, in modern gear) power supplies throughout
  $endgroup$
  – ThreePhaseEel
  Mar 21 at 3:17
  

  
  
  
  

add a comment | 

$begingroup$

AC mains is a audio frequency so capacitors large enought to pass audio will not effectively block AC hum. use an audio isolating transformer instead.

Small transformers are available for line level signals, and larger ones for loudspeaker signals.

isolation is no needed between a floating and a fixed device unless the floating device must stay floating.

share|improve this answer

edited Mar 21 at 21:50

answered Mar 21 at 3:07

JasenJasen

11.5k1531

$endgroup$

share|improve this answer

edited Mar 21 at 21:50

answered Mar 21 at 3:07

JasenJasen

11.5k1531

answered Mar 21 at 3:07

JasenJasen

11.5k1531

answered Mar 21 at 3:07

JasenJasen

11.5k1531

1

$begingroup$

No, your circuit won't work as expected. The capacitor in the audio ground is connected to the two grounds so if they are at different DC potentials it will simply charge up and stay there at that potential difference, with no current flowing.

Which tells us the real answer; if both audio circuits are grounded and the grounds may be offset, just disconnect the audio return wire with a "ground lift" switch. Note, it is not safe to disconnect an actual circuit/safety ground, just the audio ground connection between the two. So then you just have one wire carrying the signal, with a capacitor in it.

In other words, just avoid a ground loop by not connecting the two grounds together.

share|improve this answer

answered Mar 21 at 7:14

Ian BlandIan Bland

1,9861714

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Joining the two grounds does charge the capacitor to keep it at that potential, leaving no current flowing for DC offsets. I'm sure that that is not an issue. It means both are effectively ground for DC which is what the circuit neeeds
  $endgroup$
  – CL22
  Mar 21 at 18:36
  
  

  
  
  
  

add a comment | 

1

$begingroup$

No, your circuit won't work as expected. The capacitor in the audio ground is connected to the two grounds so if they are at different DC potentials it will simply charge up and stay there at that potential difference, with no current flowing.

Which tells us the real answer; if both audio circuits are grounded and the grounds may be offset, just disconnect the audio return wire with a "ground lift" switch. Note, it is not safe to disconnect an actual circuit/safety ground, just the audio ground connection between the two. So then you just have one wire carrying the signal, with a capacitor in it.

In other words, just avoid a ground loop by not connecting the two grounds together.

share|improve this answer

answered Mar 21 at 7:14

Ian BlandIan Bland

1,9861714

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Joining the two grounds does charge the capacitor to keep it at that potential, leaving no current flowing for DC offsets. I'm sure that that is not an issue. It means both are effectively ground for DC which is what the circuit neeeds
  $endgroup$
  – CL22
  Mar 21 at 18:36
  
  

  
  
  
  

add a comment | 

$begingroup$

No, your circuit won't work as expected. The capacitor in the audio ground is connected to the two grounds so if they are at different DC potentials it will simply charge up and stay there at that potential difference, with no current flowing.

Which tells us the real answer; if both audio circuits are grounded and the grounds may be offset, just disconnect the audio return wire with a "ground lift" switch. Note, it is not safe to disconnect an actual circuit/safety ground, just the audio ground connection between the two. So then you just have one wire carrying the signal, with a capacitor in it.

In other words, just avoid a ground loop by not connecting the two grounds together.

share|improve this answer

answered Mar 21 at 7:14

Ian BlandIan Bland

1,9861714

$endgroup$

share|improve this answer

answered Mar 21 at 7:14

Ian BlandIan Bland

1,9861714

answered Mar 21 at 7:14

Ian BlandIan Bland

1,9861714

answered Mar 21 at 7:14

Ian BlandIan Bland

1,9861714