I have an active x-over that uses xlr plugs. I would like to use it in a hifi system. So I have made some xlr too rca leads. I have done this years ago, and this time followed drawings online, which seem the same. It's struck me that something is wrong though.
Here is an image, to get us on the same page
Both pictures are the same. Pin1 is ground. Pin2 is signal+ and pin3 is the inverted signal. Signal-
Now from my pre-amp to the x-over input I'm happy to use these leads. It's coming out the x-over to the amps that concerns me. This lead is connection the out of phase audio too ground. A short circuit.
One idea I'm having, is that a balanced pairs amplitude is taken from the audio signals, perhaps with no reference made to ground. So this shorting of pin3, the inverted signal, is setting up the ground reference I would need for using just pin2, the signal+
If that were the case, wouldn't a resistor be a better idea than a dead short.
I have made another error I think. So far we have spoke about the 3 pins. My connectors have a 4th, the connector body. I have tied my shield to this before pins 1&3 as a mechanical tether. The xrl's cable clamp wouldn't hold my rca cable, and even stuffing it was getting out of hand. I know this could be a ground loop issue I have to look at again, but for now I'm hoping to ignore this. I just had to own up, in the interest of a complete story.
On a different note, the x-over uses female sockets as input, and male sockets for the output. This means, the output is present on pins that are not shrouded. This tells me that grounding the signal won't actually break anything. As it's almost certain that a 1/4 jack will be offered up at some point.When your elbow deep up the back of a rack, in a dark booth, and simply can't stop the show to actually see what your doing. Or, simply, a pen with a metal clip falls down the back of your rack.
Apart from telling me it's safe to ground the socket, it also leaves me scratching my head over the use of male&female sockets being used seemingly in the wrong places.
So, who will clear this up for me?
Here is an image, to get us on the same page
An externally hosted image should be here but it was not working when we last tested it.
Both pictures are the same. Pin1 is ground. Pin2 is signal+ and pin3 is the inverted signal. Signal-
Now from my pre-amp to the x-over input I'm happy to use these leads. It's coming out the x-over to the amps that concerns me. This lead is connection the out of phase audio too ground. A short circuit.
One idea I'm having, is that a balanced pairs amplitude is taken from the audio signals, perhaps with no reference made to ground. So this shorting of pin3, the inverted signal, is setting up the ground reference I would need for using just pin2, the signal+
If that were the case, wouldn't a resistor be a better idea than a dead short.
I have made another error I think. So far we have spoke about the 3 pins. My connectors have a 4th, the connector body. I have tied my shield to this before pins 1&3 as a mechanical tether. The xrl's cable clamp wouldn't hold my rca cable, and even stuffing it was getting out of hand. I know this could be a ground loop issue I have to look at again, but for now I'm hoping to ignore this. I just had to own up, in the interest of a complete story.
On a different note, the x-over uses female sockets as input, and male sockets for the output. This means, the output is present on pins that are not shrouded. This tells me that grounding the signal won't actually break anything. As it's almost certain that a 1/4 jack will be offered up at some point.When your elbow deep up the back of a rack, in a dark booth, and simply can't stop the show to actually see what your doing. Or, simply, a pen with a metal clip falls down the back of your rack.
Apart from telling me it's safe to ground the socket, it also leaves me scratching my head over the use of male&female sockets being used seemingly in the wrong places.
So, who will clear this up for me?
That gender configuration has been used for many decades on professional gear.
Without knowing the type of output interface your active crossover has, it's impossible to determine if the pin 3 to pin 1 "short" circuit would be a problem. However, I'm relatively sure it won't be since professional gear is built to tolerate this type of unbalanced conversion. Most likely there's a build-out series resistor of some sort and the short-circuit really isn't a direct short. (You won't damage anything.)
Dave.
Without knowing the type of output interface your active crossover has, it's impossible to determine if the pin 3 to pin 1 "short" circuit would be a problem. However, I'm relatively sure it won't be since professional gear is built to tolerate this type of unbalanced conversion. Most likely there's a build-out series resistor of some sort and the short-circuit really isn't a direct short. (You won't damage anything.)
Dave.
Thanks Chaps. I see from the use of male outputs that grounding won't bust it. I briefly asked the question elsewhere before deciding a separate thread was needed. A poster over there suggested that loading the output unnecessarily, would in turn load the power supply unnecessarily. I guess with ~100ohm in line I'm just dragging down a tiny signal, which I can certainly live with. It's still bothering me why though. Could I of saved myself a bit of solder, while doing a better job, simply not grounding it.
As a little padding, this is my x-over and there are some good detailed pics of the board
Celestion Easylife Active Crossover | eBay
They're auctioning off around £20 which is little more than leads cost.
As a little padding, this is my x-over and there are some good detailed pics of the board
Celestion Easylife Active Crossover | eBay
They're auctioning off around £20 which is little more than leads cost.
What you say has a base since modern Balanced Out never ever uses a transformer (unless we are talking very expensive or "vintage specs" gear) but 2 small "power amps" capable of driving 600 ohm with no problems.
And yes, you will be needlessly loading the pin 3 amp with quite low 100 ohm resistor ... in exchange of nothing.
IF it were me, I would:
a) properly identify the *output* cable (red tape, whatever) knowing it´s to be used *only* in that duty, and
b) wire only pins 1 and 2 at the XLR end, leaving 3 floating , OR wire XLR normal but not connect and tape the pin 3 wire.
And yes, you will be needlessly loading the pin 3 amp with quite low 100 ohm resistor ... in exchange of nothing.
IF it were me, I would:
a) properly identify the *output* cable (red tape, whatever) knowing it´s to be used *only* in that duty, and
b) wire only pins 1 and 2 at the XLR end, leaving 3 floating , OR wire XLR normal but not connect and tape the pin 3 wire.
The topic of what to do with Pin 3 in a configuration like this has come up numerous times on diyaudio through the years. Without knowing what the output schematic of this particular unit looks like exactly, it's always better to advise a default of grounding Pin 3. (Unless/until further information comes forward.)
Dave.
Dave.
The information which I have gleaned from my research is as follows:
Leaving the inverted signal floating (unconnected) suits both impedance balanced outputs and active balanced outputs.
The inverted signal should be connected to ground for transformer balanced outputs.
Not all sources, even professional ones, are reliable and the above info is the safe bet!
@scottjoplin - If both the source and the destination items are grounded via their power cables then breaking the shield connection will prevent a ground loop and the resulting hum.
If only one item is grounded via its power cable then the shield connection may have to be reinstated.
Leaving the inverted signal floating (unconnected) suits both impedance balanced outputs and active balanced outputs.
The inverted signal should be connected to ground for transformer balanced outputs.
Not all sources, even professional ones, are reliable and the above info is the safe bet!
@scottjoplin - If both the source and the destination items are grounded via their power cables then breaking the shield connection will prevent a ground loop and the resulting hum.
If only one item is grounded via its power cable then the shield connection may have to be reinstated.
@scottjoplin
In the spirit of being factual can you explain why inteconnect No.1 would not work very well?
My son uses this method of connection between his mixer/interface which has balanced TRS outputs and his monitoring amp which has unbalanced RCA inputs.
There is no hum but, of course, this method of connection reduces the voltage signal by 3dB as the inverted signal is not flipped and summed.
This interconnect doesn't appear to give him any trouble in his application.
In the spirit of being factual can you explain why inteconnect No.1 would not work very well?
My son uses this method of connection between his mixer/interface which has balanced TRS outputs and his monitoring amp which has unbalanced RCA inputs.
There is no hum but, of course, this method of connection reduces the voltage signal by 3dB as the inverted signal is not flipped and summed.
This interconnect doesn't appear to give him any trouble in his application.
@scottjoplin
That would be generally the case but on the other hand, forming a ground loop may also pick up RFI (to add to the induced hum).
A case of horses for courses?
I think you said to always ground the inverting input?
IMO the only time that is certain not to upset the source equipment is when the output is transformer balanced.
Sorry, you didn't say always!
That would be generally the case but on the other hand, forming a ground loop may also pick up RFI (to add to the induced hum).
A case of horses for courses?
I think you said to always ground the inverting input?
IMO the only time that is certain not to upset the source equipment is when the output is transformer balanced.
Sorry, you didn't say always!
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