Assuming the DIY case of a chassis mount XLR rather than pcb mount what is the difference. On inspection (no calculation), with a thick lead from pin one to chassis you should get lower inductance to gnd with SM caps between the pins rather than from pins to chassis?
Clearly if you are doing a PCB you can do a 'proper job' (https://www.youtube.com/watch?v=glcZVVCBBvs for those who don't know where 'proper job' comes from from)
A Neutrik emc plug and socket runs £13 so for my active setup that would be £130 for phase 1. For the peace of mind and expectation bias probably a good investment.
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I have metal chasis mount XLR sockets.
They make electrical contact to the chassis intermitantly around the perimeter and via the 2 bolt fixing. I have drilled and inserted 2 extra bolts to make a 4bolt fixing in a few.
I then attach/solder 3 off 47pF leaded ceramic NP0 caps around the 3 poles on the back of the socket using the shortest possible leads. And solder a further very short lead from Pin1 to the nickel plated socket.
The socket has fairly effectively become an extension of the Chassis.
47pF pin2 to pin3 attenuates differential mode interference using upstream resistance and inductance of the interconnect.
47pF pin2 to pin1 and 47pF pin3 to pin1, attenuate common mode interference using upstream resistance and inductance of the interconnect.
So far I have only done this conversion to one power amplifier and after 6months use I can say it sounds like it performs flawlessly.
I intend converting more of my power amps to filtered XLR inputs instead of RCA/Phono.
They make electrical contact to the chassis intermitantly around the perimeter and via the 2 bolt fixing. I have drilled and inserted 2 extra bolts to make a 4bolt fixing in a few.
I then attach/solder 3 off 47pF leaded ceramic NP0 caps around the 3 poles on the back of the socket using the shortest possible leads. And solder a further very short lead from Pin1 to the nickel plated socket.
The socket has fairly effectively become an extension of the Chassis.
47pF pin2 to pin3 attenuates differential mode interference using upstream resistance and inductance of the interconnect.
47pF pin2 to pin1 and 47pF pin3 to pin1, attenuate common mode interference using upstream resistance and inductance of the interconnect.
So far I have only done this conversion to one power amplifier and after 6months use I can say it sounds like it performs flawlessly.
I intend converting more of my power amps to filtered XLR inputs instead of RCA/Phono.
Mogami W2901 is the smallest OD balanced cable with a braided shield I'm aware of.
Mini XLR may also be worth a look. Some of the connectors are more than decent from an EMC perspective, though unfortunately they tend to be priced accordingly.
That's really up to the builder to decide based on the specifications of whatever cables they're considering. A spread on the order of 50 pF/m K1 and 25 pF/m K0 isn't particularly significant for home audio. Even with a conservatively compensated line driver using 220 ohm RISOs it takes more than a few nF to move the RC cutoff low enough to start creating audio band phase error of any significance.
Change the application to the longer runs of pro audio and, yeah, it's probably not the greatest idea. Though, pragmatically speaking, the reduced mechanical durability of a smaller OD is likely to be more of a problem.
Change the application to the longer runs of pro audio and, yeah, it's probably not the greatest idea. Though, pragmatically speaking, the reduced mechanical durability of a smaller OD is likely to be more of a problem.
I do. Off the top of my head I recall the THD being ever so slightly higher with a 4 Ω load than with 8 Ω load, just as is the case for the PAR86. On ±28 V rails, the MOD86 provides 60-65 W into 4 Ω before the THD starts to rise. Note that the 68 W number in the data sheet for the LM3886 is at 1 % THD, so be careful when comparing numbers. I generally don't push the amp that hard into clipping in my measurements.
In a differential driver, the performance is determined largely by the matching between resistors surrounding the opamp(s) and the parasitics of the layout connecting to the resistors. While you can buy matched resistor networks, they're a bit pricy and usually not very layout friendly. For the THAT Driver, I chose the THAT16xx-series and chose to let THAT Corp.'s engineers worry about the resistor matching.
I also don't know how the TI part behaves when one output is shorted to ground, as it would be if the user plugged the differential driver into a single-ended input. Unlike many SE->DIFF circuits, the THAT part provides good performance, even in this condition.
Tom
Thanks Twest, looks like a great cable. I do have some MiniXLR I bought for evaluation. They are great in their smallness, and even have a locking feature. Full metal jacket will provide fair amount of shielding. I just missed thin cable to start using them.
Wouldn't mind at all if this plug became the standard for home use.
Wouldn't mind at all if this plug became the standard for home use.
Some coax exceeds 150pF/m
3m of that combined with a Receiver RF filter and you can approach 1nF of capacitance that has to be charged and discharged by the Source.
It's not just the resistive output impedance of the source that limits the ability to drive the cable. The current capability of the Source also has an effect.
Take the excellent B1 using BL grade 2sk170 as the output device.
Maximum output current can be as low as 6mApk.
If you try to exceed this you are into current clipping. But before you reach current clipping the Buffer is already into a region of current induced distortion.
One limits the maximum voltage to avoid voltage induced distortion, similarly one must limit maximum current demand to avoid current induced distortion.
What would be a reasonable maximum current for a B1?
That same analysis should be applied to any Source that is required to drive a cable & filter.
One must look at current capability AND output impedance.
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As I understand it tiny XLR is Rean's (Neutrik) name for mini XLR. However, I've never bought a set of Rean and Switchcraft parts to verify they fit together---the part drawings leave off a few critical dimensions. Not sure where the naming's going. It's not a standardized interface and Switchcraft includes tiny in the names some of their mini XLR series.
The 28-30 AWG (0.05-0.08 mm^2) conductors may pose an issue for durability in a pro setting as well. That's rather skinny wire. The GLS Audio cable I usually use features 22 AWG (0.3 mm^2) conductors. The GLS cables are nothing fancy, but good enough for my needs. Not that I'm involved with pro audio, yet. I just don't like soldering to angel hair, that's all...
Tom
Should be OK in most cases ... as is AndrewT's method.
But its not the connection to p1 that's important. It's the connection to chassis. You may not want to connect p1 to chassis for other reasons ... but then you must connect it to chassis with 100n ceramic with short leads.
Just a reminder to all that XLR p1 ISN'T connected to chassis unless you do this explicitly.
AndrewT, the socket SHOULD be an extension of the chassis. It's part of the Faraday cage.
Was is das B1?
You can pay MUCH more for Golden Pinnae mains cable
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No measurements? Shame. My method should be the same as Andrews. Where did I deviate? If there is something that the DIY'er can do easily that gets within a GnatFart of the ultimate then that gets thumbs up from me.
Accepted, but given how many get it wrong, including those who really should know better, leading with pin1 to chassis is not a bad mantra. Which leads to how, for the DIY'er do you get a low inductance 100n path to chassis from Pin1 reliably?
The LM3886 is currently limited and if you look at the spec (figure 33) you will see that power output drops like a stone below 4Ohms. I am going to be running into 3Ohm ribbons and taking a risk. You should get between 20-30W into 2 Ohms if you keep the supply nice and low, but I would not guarantee it (interesting test though).
I thought I had made that clear. If there is reliable electrical contact around the metal shell of the XLR socket to the metal of the enclosing chassis, then the socket shell becomes part of the enclosing chassis.
Pass describes his B1 Buffer for us. He donated his IP to our cause.
There is the version known as DCB1 which is a DC coupled Buffer.
I would use a very short link from Pin1 to shell. Then electrical contact from shell to chassis. This is lowest inductance.
If a special connection is needed from a Source to a Receiver that requires the shield to be capacitor coupled at the Receiver end, then I would use a special cable that connects shield to Pin1 inside the plug. And label it clearly and unambiguously.
Whitlock (Jensen) shows/suggests this in one, or more, of his papers.
Which I agree with, but kgrlee seemed to suggest he knew a better way of getting pin to chassis. Was hoping to find out what it was as I can't personally think of one rather than accepting the neutrik EMC connectors as being fine value for what they give you.
http://imageshack.com/i/1aimpedancevariationexampg
Impedance trend of coaxial interconnects I took a Very long time ago.
Impedance trend of coaxial interconnects I took a Very long time ago.