A yes/no possible ground loop (?) question

[agedhorse]

Initially I also thought that, but don't forget that the red (hot) wire is supposed to be insulated behind the metallic foil, and that the shield (ground) wire is supposed to be outside it. If you reverse hot and ground on both ends of the cable you still get a pinout where 1 goes to 1, 2 to 2 etc., but the insulation is reversed. I am going to test it right now and report back!

But this is wrong, pin 1 has a VERY specific function.

 

[Redbrangus]

I am now going to re-solder this properly.

There you go. Finally.

But then, that's no guarantee that is going to resolve all your problems -- there's still the potential problem of input levels on your interface. On the Focusrite stuff, the XLR part of the combo connector is mic level only...don't know if it's that way on yours or not. I know some are switchable in software.

Remind me again why you didn't just use the unbalanced, TS 1/4"-phone connections? I seem to remember you said they were dead silent.

 

[Wasnex]

Again, if you use that incorrectly wired cable, you will be putting the 'hot' signal onto the shield of the cable -- and the subsequently induced hum problem is likely exacerbated by the fact that one or both of the devices being interconnected is/are likely to not be truly balanced. I'm saying again -- that cable is incorrectly wired, Google-search generated images to the contrary notwithstanding.

If I understand what you are saying.

I screwed up the image in post #6 . I was modifying the image and lost my train of thought , and then forgot I was making the change. Sorry for the confusion. It's edited and is hopefully correct now and the wiring convention matches reality and the second image I posted in #9.

 

[Trilobita]

Ok, so I flipped and re-soldered the wires and the hum is noticeably less bad but it is definitely still there when the interface is powered on. When it is powered off it is now picking up some random radio station...

I checked the manual of my interface (Steinberg CI-1), where I found the following:

"You can directly connect an electric guitar or electric bass without the need for a separate DI box or amp simulator to analog input jack 1. In this case, turn on the HI-Z button on the front panel. Make sure to use an unbalanced phone [probably should read "phono"] cable when you connect an electric guitar or electric bass. If you use a balanced cable, it will not work correctly."

There you go. Finally.
Remind me again why you didn't just use the unbalanced, TS 1/4"-phone connections? I seem to remember you said they were dead silent.

I just wanted to rule out any problems with the XLR out of the ART unit. As long as I am sure whatever is happening is not a problem with the ART XLR out, then I am cool with it. Do you think I can rule that out at this point?

 

[Redbrangus]

Well, it doesn't rule out much of anything, but you don't have any indication that there IS something wrong -- it sounds like interface issues that could be resolved. The stuff about the Steinberg input is valid such as it is, but you're not plugging your bass into the Steinberg -- you're plugging your bass into the ART and then plugging IT into the input of the Steinberg. That's a different thing.

So nowhere in the manual for the Steinberg is there any indication of what the input level of the XLR is? As I say, I suspect it's mic-level, but I'm not sufficiently motivated to look it up for my own self. Or rather, for you.

Edit: "Phone" plug (or cable) is correct enough; it's short for "telephone", which was the original use for that connector, or at least a similar, same-sized one. "Phono" is short for phonograph, of course.

 

[Trilobita]

The "Analog input" of the CI-1 is said on its manual to be rated as follows for the XLR input:

Nominal level: -60dBu to -16dBu
Maximum level: -6dBu
Input impedance: 3kΩ

Other than that, the ART preamp has a switch that allows me to choose between instrument out and line out, and regarding the XLR out the ART preamp manual says:

"You can connect the XLR output jack of the Tube MP/C to the XLR input of your mixer, however most affordable
mixers do not allow you to bypass their internal preamp when using the XLR jack. Use the Output switch and set it to the
Inst. mode when connecting to a mic preamp. This will lower the output noise of the Tube MP/C and prevent overloading the input of the mic preamp."

Unfortunately I don't understand the CI-1 numbers well enough to know what the result was supposed to be like, but the "This will lower the output noise of the Tube MP/C..." part on the manual of the ART preamp makes me think that some level of noise would be expected anyway? Because even the lowest output level of the ART would be significantly high for what the CI-1 is expecting to get?

 

[beans-on-toast]

The cable has noise printed right on it, that gotta be a bad sign.

Not all cables are created equal, it really makes a difference. It doesn’t have to be expensive but you want it put together properly with good connectors and a quality cable.

Also is the cable just long enough or long and looped around. Cable runs are important. Check if it runs near computer or any other power supplies, or a computer monitor. This can result in an issue.

 

[Wasnex]

The "Analog input" of the CI-1 is said on its manual to be rated as follows for the XLR input:

Nominal level: -60dBu to -16dBu
Maximum level: -6dBu
Input impedance: 3kΩ

Other than that, the ART preamp has a switch that allows me to choose between instrument out and line out, and regarding the XLR out the ART preamp manual says:

"You can connect the XLR output jack of the Tube MP/C to the XLR input of your mixer, however most affordable
mixers do not allow you to bypass their internal preamp when using the XLR jack. Use the Output switch and set it to the
Inst. mode when connecting to a mic preamp. This will lower the output noise of the Tube MP/C and prevent overloading the input of the mic preamp."

Unfortunately I don't understand the CI-1 numbers well enough to know what the result was supposed to be like, but the "This will lower the output noise of the Tube MP/C..." part on the manual of the ART preamp makes me think that some level of noise would be expected anyway? Because even the lowest output level of the ART would be significantly high for what the CI-1 is expecting to get?

That appears to cover mic and instrument level, but not really line level (+4dBu). If the XLR out on your preamp is line level, then yes I would expect the signal to noise (S/N) ratio to be compromised a bit. In order to get the best S/N ration, you must use proper gain staging. This is not possible when one unit provides a different signal level than the next unit expects.

 

[Redbrangus]

The interface's XLR is clearly intended to be a mic input. If you selected the minimum amount of input gain and used the "instrument" output of the ART, it could probably be made to work. The "Hi-Z" selector on the interface should NOT be activated, BTW. But it sounds like that interface really needs to see a high-level signal like the output of the ART on it's 1/4"-phone (T-S), line-level input connector. You were doing it right in the first place.

 

[byacey]

Well I just kept testing and noticed that if all the connections are made as above using the ART's instrument (TS) in for the bass and the XLR out into my Steinberg interface XLR in, the hum occurs even when the ART unit is completely turned off and even unplugged from power. If I touch the metal chassis of the unit, the hum reappears. Also, even when I unplug the bass so as to make the hum go away, touching the metal chassis of the unit makes the hum come back.

I also unscrewed the tips of my only XLR cable and found that pin 1 (the one on the upper left if you looking directly to the prongs of the male connector on a fully assembled cable) connects to the hot (red) wire whereas pin 2 (just beside it) connects to the ground (shield) wire on both ends of the cable. I am posting a picture of both ends - in this picture, you are seeing the wiring slightly from above (meaning the two parallel pins that are next to each other are closer to your eyes, whereas the lone cold pin is closer to the surface of the table).

I guess these pins 1 and 2 should be wired the other way around, right? Or should it simply not matter because both ends are wired the same kind of wrong? The manual of the ART preamp specifically says that it expects pin 1 as ground and pin 2 as hot. I couldn't find this sort of information about my Steinberg interface. (I'll be happy to lift pin 1 and report back during the re-soldering process once someone tells me what's the best way to go from here.)

View attachment 4247194

It appears 1 and 2 are reversed on both connectors. All common mode rejection goes out the window with signal on the shield.

 

[byacey]

It’s hard to tell from the photo, but by chance does one of the wires connect to the shell terminal of the female connector?

That picture is consistent of inexpensive off-shore XLR cables, commonly riddled with issues.

That, or the guy making the cable was asleep at the switch.

I knew of a guy years ago that was making a snake cable up with 56 pair cable. He did a beautiful job, with sleeves on all the shields, and the dressing was a truly a work of art. The only problem was he had pin 1 and 2 flipped on every connection.

 

[Wasnex]

That, or the guy making the cable was asleep at the switch.

I knew of a guy years ago that was making a snake cable up with 56 pair cable. He did a beautiful job, with sleeves on all the shields, and the dressing was a truly a work of art. The only problem was he had pin 1 and 2 flipped on every connection.

I hate it when that happens .

 

[Redbrangus]

I know a guy who put on the multi-pin connector for a 40-channel snake without putting the connector's back shell on first. Know that guy pretty well...for some 68 years now.

 

[byacey]

I know a guy who put on the multi-pin connector for a 40-channel snake without putting the connector's back shell on first. Know that guy pretty well...for some 68 years now.

Yeah, that bites.

 

[Trilobita]

It’s hard to tell from the photo, but by chance does one of the wires connect to the shell terminal of the female connector?

That picture is consistent of inexpensive off-shore XLR cables, commonly riddled with issues.

This comment had escaped my attention and I only saw it when it was quoted above. You are right in that this is a cheap cable sent from Hong Kong though I bought it "from England" on eBay. There is nothing connected to anything else apart from a wire to each pin. I'll check what that shell terminal is supposed to be connected to and try to fix it. Thanks for calling my attention to that.

 

[Trilobita]

Well, I don't want to end the discussion (feel absolutely free to write away and I'll continue checking the thread out and participating in it) but I would like to sincerely thank everyone who replied. This was a longer yes/no question than I had initially anticipated, but so far it has been quite more useful, too!

 

[Redbrangus]

Don't connect the shell lug to anything...it will be fine.

 

[agedhorse]

That, or the guy making the cable was asleep at the switch.

I knew of a guy years ago that was making a snake cable up with 56 pair cable. He did a beautiful job, with sleeves on all the shields, and the dressing was a truly a work of art. The only problem was he had pin 1 and 2 flipped on every connection.

Ouch, damn that made for a crappy discovery!

I know a guy who put on the multi-pin connector for a 40-channel snake without putting the connector's back shell on first. Know that guy pretty well...for some 68 years now.

I know that guy pretty well too... happens at least once to anybody who fabricates such cables. Was it an EDAC/ELCO connector?

This comment had escaped my attention and I only saw it when it was quoted above. You are right in that this is a cheap cable sent from Hong Kong though I bought it "from England" on eBay. There is nothing connected to anything else apart from a wire to each pin. I'll check what that shell terminal is supposed to be connected to and try to fix it. Thanks for calling my attention to that.

The shell terminals should not be connected to anything.

 

[1958Bassman]

When searching for the info about balanced audio noise problems, entering 'common mode noise issues' usually shows the best solutions. MIX Magazine had an article a long time ago titled 'The Pin 1 Problem' and searching for that phrase is another great way to get info.

Here's a white paper from Rane, who has a whole site devoted to technical info-

Pin 1 Revisited