I've done that a few times as well. It works rather well. I did notice at one point that Digikey had some mounting brackets for that exact purpose. They weren't that expensive as I recall.
Tom
I'm guessing you're referring to "The G Word" by Bruno Putzeys.
A differential connection requires two pins for the signal pair and one pin for the cable shield. That's why an XLR connector has three pins. You are correct that if the cable shield could reliably be connected to the connector shell, you could do away with pin 1 - in theory. Doing away with pin 1 would require the cable shield to be connected to the connector shield. That has many advantages from an EMI perspective, but does set up a ground loop that some may want to avoid. Also, some XLR connectors are painted or made of plastic so they wouldn't make any connection to the shield. At the other end of the spectrum, you have the Neutric XCC-series which are touted to provide superior EMC performance and do offer a solid connection to the connector shell. Bringing the cable shield in on a separate pin also makes it possible for the chassis connector shell to float, if that's desired.
How to connect pin 1 is a subject of considerable debate - at least in the DIY world. I'm fairly certain it's a settled matter in the professional world.
In addition to Bruno's paper, you may also gain some insight from Rane Corp's application note or the AES48-2005 standard.
Tom
Yes, steel.
I picked up an 1/8" x 1" x 4' piece of AL flat bar at Lowe's. It will work for a spreader as easily as it would for mounting bars.
They'll probably find that my speakers aren't as good as your amps...
Cool, but my chassis is too short to turn the board that way.
Thanks Tom,
I read the Rane paper and found it a great aid to help expand my meager understanding of electronics.
The recommended XLR connection seems to have an added option not on page 9 fig 24 of the "G Word" and that is the XLR body grounding to the chassis.
I think that, because my chassis and XLRs are metal, it will be able to easy make the recommended connections just by soldering the shield and another wire to pin1. The extra wire would be connected to the chassis. The body to chassis grounding should happen just by screwing the XLR to the chassis. Am I missing something?
My Neutrik NC3FD-LX-HE XLRs have a small tab connected to the body but it seems redundant to use it since the chassis and XLR are metal. Is that correct?
I read the Rane paper and found it a great aid to help expand my meager understanding of electronics.
The recommended XLR connection seems to have an added option not on page 9 fig 24 of the "G Word" and that is the XLR body grounding to the chassis.
I think that, because my chassis and XLRs are metal, it will be able to easy make the recommended connections just by soldering the shield and another wire to pin1. The extra wire would be connected to the chassis. The body to chassis grounding should happen just by screwing the XLR to the chassis. Am I missing something?
My Neutrik NC3FD-LX-HE XLRs have a small tab connected to the body but it seems redundant to use it since the chassis and XLR are metal. Is that correct?
Since being exposed to some very good info I'm surprised my existing systems are so quiet.
I have to get my ear within 1 or 2 inches of the speakers, with everything on, the volume knob way up and no music playing, to hear only the slightest hiss.
All my systems use RCAs for all connections. How is that possible?
I have to get my ear within 1 or 2 inches of the speakers, with everything on, the volume knob way up and no music playing, to hear only the slightest hiss.
All my systems use RCAs for all connections. How is that possible?
Bill, I ran into the same issue w/ a steel bracket in the Mini Dissipante. I shared my solution in #1394. Basically, I replaced the LM-side standoffs w/ right angle brackets and drill / tapped extra holes in the heatsink.
I'd probably make mounting bars. I'd rather not create more thermal resistance it's possible to avoid it.
Tom
The thing that you are missing is:
There is no 'ground' in a balanced interconnect system. There is a 'shield' but it does not need to be connected to anything for the system to work.
All shield connections to the chassis should be made very near the interconnect chassis connector.
While it's true that the interconnect shield, the audio circuit common (aka ground), the DC supply common (aka ground) and the AC power Safety Ground/Protective Earth all connect to the chassis, each has a different function.
There is no 'ground' in a balanced interconnect system. There is a 'shield' but it does not need to be connected to anything for the system to work.
All shield connections to the chassis should be made very near the interconnect chassis connector.
While it's true that the interconnect shield, the audio circuit common (aka ground), the DC supply common (aka ground) and the AC power Safety Ground/Protective Earth all connect to the chassis, each has a different function.
Lonestar audio fest
Went to the local audio fest here in dallas not one DIY person uses Toms amplifiers
I was hopeful someone was going to be using...but as luck would have it no luck
anyways I have been been soldering since i was 7 years old. have used everything you can imagine ...I also had some custom 97/3 special electronics solder made over the pond LEAD FREE multicore special flux whiz bang best ever stuff ....but
IMO best soldering best flowing will be multicore savbit 60/40 vintage made in england....DO NOT BUY THE NEW STUFF ...garbage...been there ....done that
I am very experienced in soldering can you tell
Went to the local audio fest here in dallas not one DIY person uses Toms amplifiers
I was hopeful someone was going to be using...but as luck would have it no luck
anyways I have been been soldering since i was 7 years old. have used everything you can imagine ...I also had some custom 97/3 special electronics solder made over the pond LEAD FREE multicore special flux whiz bang best ever stuff ....but
IMO best soldering best flowing will be multicore savbit 60/40 vintage made in england....DO NOT BUY THE NEW STUFF ...garbage...been there ....done that
I am very experienced in soldering can you tell
That's a rather reckless recommendation. It will work fine as long as the various components involved keep their output common-mode voltages within the common-mode spec of the differential receiver.
If the line driver and line receivers are in equipment connected to different phases of the mains voltage, you will get all sorts of voltage differences between the two common-mode voltages. Granted, it will be some capacitively coupled current from the various mains filters, but it could reach upwards of 400 V (230 V, 3-phase system). The drive impedance may be high, but it's not a current I'd like to route through the ESD structures of an IC.
Tom
I'm still confused about grounding. It appears that all grounds usually end up connected, somewhere, to the chassis. Based on that, I thought; why not connect all to the same point/screw on the chassis.
After reading the Rane and G Word docs, I may understand grounding a little better.
Below is how I envision an internal grounding scheme for the following setup.
1. An AC entry IEC with ground wire connected to the chassis.
2. A shielded 2 wire cable is used, from XLR, to the amplifier.
Ideally the shield should be connected at both ends. The connection at the XLR should be shield and another wire to pin1. The other wire is then connected to the chassis as close as possible to the XLR body.
It seems that ties earth and shield together no matter where the wires are actually connected to the chassis. Based on that couldn’t the AC ground wire be connected to the same point as the pin1 to chassis wire? That is both wires under one screw. Is that correct?
It also seems that the signal ground could be connected to the same point. That would be three wires under one screw. I think, based on reading the docs, the difference/importance of the signal ground is where the other end of the wire is connected in the amplifier.
Are those assumptions correct or am I way off base?
After reading the Rane and G Word docs, I may understand grounding a little better.
Below is how I envision an internal grounding scheme for the following setup.
1. An AC entry IEC with ground wire connected to the chassis.
2. A shielded 2 wire cable is used, from XLR, to the amplifier.
Ideally the shield should be connected at both ends. The connection at the XLR should be shield and another wire to pin1. The other wire is then connected to the chassis as close as possible to the XLR body.
It seems that ties earth and shield together no matter where the wires are actually connected to the chassis. Based on that couldn’t the AC ground wire be connected to the same point as the pin1 to chassis wire? That is both wires under one screw. Is that correct?
It also seems that the signal ground could be connected to the same point. That would be three wires under one screw. I think, based on reading the docs, the difference/importance of the signal ground is where the other end of the wire is connected in the amplifier.
Are those assumptions correct or am I way off base?
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Please see my comment about the common-mode voltage.
I recommend connecting the MOD86 as I have shown in the design documentation.
Tom
You did interpret the G Word correctly as far as I can tell. You just missed the bit about the differential receiver having a finite common-mode voltage range. The same goes for a line transformer. If the common-mode voltage exceeds the dielectric breakdown of the insulation between primary and secondary, the transformer gets rather unhappy.
Tom
Tom
Because that dramatically increases the impedance from the cable shield to ground.
The whole point of connecting the cable shield to the chassis is to route all the RF energy injected onto the shield to ground so it does not enter the chassis. In the ideal world, you would drill a hole in the chassis just large enough to fit the cable shield through and solder the shield to the chassis all the way around the circumference of the cable shield. This is common practice in many RF circuits where connections between modules are made that way. It is not common in audio as most people prefer to have the ability to unplug their interconnects. So now we need a connector in there. By convention:
XLR Pin 1 = Cable shield
XLR Pin 2 = Hot (+)
XLR Pin 3 = Cold (-)
To get close to the perfect solder seal around the cable entry, connect pin 1 to the chassis with as short a wire as possible right at the XLR connector. If you route pin 1 to a central grounding point within the chassis, you've now set up an antenna inside the chassis that can radiate all the RF energy imposed on the cable shield within your chassis. That's an EMI no-no.
If you want to get even closer to the ideal world, you'd use something like Neutrik's XCC series where the connector shell is connected to the cable shield along the entire circumference of the shield and the shell is connected to the chassis with a bunch of little leaf springs. This is the perfect solution if you live atop a radar tower or if your livelihood depends on the signal integrity on those XLR cables (TV/radio stations).
While the differential line receiver only should care about the differential voltage, i.e. V(Hot) - V(Cold), any real differential line receiver requires the common-mode voltage to remain within a certain voltage range (input common-mode voltage range). This means that in addition to caring about the differential voltage, Vdiff = V(Hot) - V(Cold), it also cares about the common-mode voltage, Vcm = V(Hot)/2 + V(Cold)/2. You need the ground connection such that the various pieces of equipment can agree on what Vcm should be. You also need the ground connection (cable shield) to provide shielding against any RF imposed on the signal pair. After all, the quality of the twist in the twisted pair and the CMRR of the line receiver are both finite quantities.
I'm seeing a support page about differential signalling in my future. I have quite a bit to add to my Taming the LM3886 series as well. So many projects. Still only 24 hours in a day.
Tom