For impedance balanced outputs grounding cold is OK but not for active balanced -that's what I've read.
As the manual for my son's interface does not state the type of balanced output it employs, I took no risks and left the cold floating.
P.S. I do know it's not a transformer balanced output!
Here is a summary which represents the facts as I've researched them. When connecting a balanced output to an unbalanced input the rules are:
1. Impedance balanced outputs - cold can either be left floating or connected to the shield.
2. Active balanced outputs - cold must be left floating.
3. Transformer balanced outputs - cold must be connected to the shield.
In all three cases, the shield is connected to pin 1 of the XLR.
As the manual for my son's interface does not state the type of balanced output it employs, I took no risks and left the cold floating.
P.S. I do know it's not a transformer balanced output!
Here is a summary which represents the facts as I've researched them. When connecting a balanced output to an unbalanced input the rules are:
1. Impedance balanced outputs - cold can either be left floating or connected to the shield.
2. Active balanced outputs - cold must be left floating.
3. Transformer balanced outputs - cold must be connected to the shield.
In all three cases, the shield is connected to pin 1 of the XLR.
Well as the OP, I've been sat back watching this unfold, unable to add any more. I must say, I particularly like the idea of the 150ohm resistor. Before posting, I had a higher value in mind, but felt there was probably a lot of room for maneuver. It does seem the compromise between the two opposing ideals of do or don't connect it.
I can't find the older threads. I imagine the search engine won't accept 3 letter words. A shame when so much here is abbreviated. So I'm going to do myself a favour. xlrr too rcaa. I do this occasionally, for obvious reasons.
If grounding is in no way setting up a relationship between the positive signal wire and ground, I think it's going to be a pointless action for me. I'm not driving a transformer, just a high impedance input. I'm not satisfied leaving it connected now it's done either. I will revisit the job (a long reach behind me) and fit half a K perhaps. Just to be sure I've not left a filter ringing away. That half K along with a ~100ohm internally, will give me a reasonable 600ohm.
Have I gone insane, or does this look like a reasonable choice. Treading carefully between my own ideas and those thankfully received here.
I can't find the older threads. I imagine the search engine won't accept 3 letter words. A shame when so much here is abbreviated. So I'm going to do myself a favour. xlrr too rcaa. I do this occasionally, for obvious reasons.
If grounding is in no way setting up a relationship between the positive signal wire and ground, I think it's going to be a pointless action for me. I'm not driving a transformer, just a high impedance input. I'm not satisfied leaving it connected now it's done either. I will revisit the job (a long reach behind me) and fit half a K perhaps. Just to be sure I've not left a filter ringing away. That half K along with a ~100ohm internally, will give me a reasonable 600ohm.
Have I gone insane, or does this look like a reasonable choice. Treading carefully between my own ideas and those thankfully received here.
That resistor is completely unnecessary. It seems, looking at the innards of your unit, it's a simple op-amp driving setup and obviously no transformers.
So, if you're going to make your own cables from a simple coax, use Pin 1 and Pin 2 and wire to the RCA connector and leave Pin 3 floating. Job done and good enough.
Dave.
So, if you're going to make your own cables from a simple coax, use Pin 1 and Pin 2 and wire to the RCA connector and leave Pin 3 floating. Job done and good enough.
Dave.
The best article on jacks and grounding is here and shows you all the combinations and recomendations.
Grounding and Shielding Audio Devices
Grounding and Shielding Audio Devices
I can't agree with Davey enough!!
Provided it is NOT a transformer balanced output then simply connect XLR pins 1 and 2 to the RCA plug and leave pin 3 floating.
P.S. If this interconnect causes hum then disconnect the shield at one end of the interconnect, either at the XLR end or at the RCA end.
Also, the interconnect should be as short as possible to mitigate against picking up noise.
Provided it is NOT a transformer balanced output then simply connect XLR pins 1 and 2 to the RCA plug and leave pin 3 floating.
P.S. If this interconnect causes hum then disconnect the shield at one end of the interconnect, either at the XLR end or at the RCA end.
Also, the interconnect should be as short as possible to mitigate against picking up noise.
Breaking the shield at one end of the interconnect is only necessary if hum and buzz turn out to be a problem.
If the devices at either end of the interconnect are connected to different power sources (mains outlets) then a potential ground loop is created. If the ground potential at the source end is different from that at the load end then hum and buzz is the likely result.
The solution is to cut the shield at one end. Some sources say it's better to cut at the high impedance (in our case RCA) end.
If it is a requirement to have both ends grounded, then placing an HF filter in the shield can help to avoid any noise.
This entails placing a 'bridging network' across the shield gap. The first interconnect diagram which I attached on page one shows an optional bridging network consisting of a resistor in series with a capacitor. However, no component values are given.
Scottjoplin suggests placing an approximately 10 ohm resistior in the gap. Perhaps he can explain his choice of resistor and in what way it would be effective.
At the end of the day, it is easier to steer clear of this type of filtering by simply grounding one end only.
If the devices at either end of the interconnect are connected to different power sources (mains outlets) then a potential ground loop is created. If the ground potential at the source end is different from that at the load end then hum and buzz is the likely result.
The solution is to cut the shield at one end. Some sources say it's better to cut at the high impedance (in our case RCA) end.
If it is a requirement to have both ends grounded, then placing an HF filter in the shield can help to avoid any noise.
This entails placing a 'bridging network' across the shield gap. The first interconnect diagram which I attached on page one shows an optional bridging network consisting of a resistor in series with a capacitor. However, no component values are given.
Scottjoplin suggests placing an approximately 10 ohm resistior in the gap. Perhaps he can explain his choice of resistor and in what way it would be effective.
At the end of the day, it is easier to steer clear of this type of filtering by simply grounding one end only.
It reduces the current flow in the shield which can be quite high, same principle as the cross channel ground loop hum breaking resistors described here https://www.updatemydynaco.com/documents/GroundingProblemsRev1p4.pdf
Thanks Scott.
There's some interesting reading in your reference, which I will need time to fully assimilate.
The third page contains a discussion of the noise voltage developed across Rgw, the ground wire resistance of a preamp to power amp interconnect.
It mentions connecting a 10 to 100 ohm resistor in series with Rgw, but only as a way of diagnosing the amount of ground loop current.
The principle of the diagnosis is that the series resistor would reveal the presence of ground loop current by making its effect worse, which would be indicated by the production of measurable hum at the power amplifier's output.
It finally notes that, the lower the resistance of the cable, the less the ground loop current gets to add to the noise.
This would appear to be at odds with your suggested solution of placing an approximately 10 ohm resistor in the shield.
There's some interesting reading in your reference, which I will need time to fully assimilate.
The third page contains a discussion of the noise voltage developed across Rgw, the ground wire resistance of a preamp to power amp interconnect.
It mentions connecting a 10 to 100 ohm resistor in series with Rgw, but only as a way of diagnosing the amount of ground loop current.
The principle of the diagnosis is that the series resistor would reveal the presence of ground loop current by making its effect worse, which would be indicated by the production of measurable hum at the power amplifier's output.
It finally notes that, the lower the resistance of the cable, the less the ground loop current gets to add to the noise.
This would appear to be at odds with your suggested solution of placing an approximately 10 ohm resistor in the shield.
I've done it on one channel whilst leaving the other connected and it's done the trick. Any hum which is not due to cross channel ground loop should be dealt with another way. The Rane notes amongst others tell how to do it, this is very informative too Audio Component Grounding and Interconnection
You're welcome, this may interest you too, some good discussion and links. Cable shield as a Faraday cage
It's worth stressing at this point in the thread that we are discussing a transformerless, balanced to unbalanced interconnect cable. Probably I've over discussed it, but here I go again!
I have looked at the references and it would appear that hum issues depend, not only on the safety ground arrangements of the equipment, but also on the exact mechanism (and there's more than one!) behind the interfering noise.
One important safety precaution: NEVER remove an equipment safety ground where fitted!
If the source and destination equipment each have safety connections to electrical ground via their power cables, then a simple break in the shield conductor at the destination end should be sufficient to remove any hum. Signal return is provided via the equipment ground connections.
There are other equipment arrangements which may require a 10 ohm resistor to be inserted into the break in the shield. The resistor contributes by maintaining sufficient ground continuity while reducing the hum.
Thanks to the other contributors who pointed the latter fact out!
I have looked at the references and it would appear that hum issues depend, not only on the safety ground arrangements of the equipment, but also on the exact mechanism (and there's more than one!) behind the interfering noise.
One important safety precaution: NEVER remove an equipment safety ground where fitted!
If the source and destination equipment each have safety connections to electrical ground via their power cables, then a simple break in the shield conductor at the destination end should be sufficient to remove any hum. Signal return is provided via the equipment ground connections.
There are other equipment arrangements which may require a 10 ohm resistor to be inserted into the break in the shield. The resistor contributes by maintaining sufficient ground continuity while reducing the hum.
Thanks to the other contributors who pointed the latter fact out!
I've not come across that remedy before. What can be done is take a cable from the source chassis, run it close to the interconnect and connect to the receiver's chassis. Then disconnect the power lead earth of the source.
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