XLR cable passes signal but ~20db lower

M

Matt Vivlamore

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Jan 11, 2011
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What would cause an XLR cable to be ~20db lower?

Last gig, the Bass Player plugs into my EWI Active DI. The DI was connected to a 10' Mogami (quad cable) connected to a 50' CBI drop 6 stage snake and into a LS9-32. Phantom power was "on". I replaced the 10' Mogami cable with a 15' EWI Starline and everything began to work properly.


Yes, I can duplicate it on other sources.

I don't know how old the cable is but it looks new. I'm not sure who built the cable, but it wasn't done by a below average guy. I'm not to concern because it was a band left behind cable.

Just mainly puzzled that the cable passes signal but it's very quiet.
 
Re: XLR cable passes signal but ~20db lower

Matt Vivlamore said:
What would cause an XLR cable to be ~20db lower?

Last gig, the Bass Player plugs into my EWI Active DI. The DI was connected to a 10' Mogami (quad cable) connected to a 50' CBI drop 6 stage snake and into a LS9-32. Phantom power was "on". I replaced the 10' Mogami cable with a 15' EWI Starline and everything began to work properly.


Yes, I can duplicate it on other sources.

I don't know how old the cable is but it looks new. I'm not sure who built the cable, but it wasn't done by a below average guy. I'm not to concern because it was a band left behind cable.

Just mainly puzzled that the cable passes signal but it's very quiet.
Click to expand...
Corrosion at the solder points can certainly acomplish that...
 
Re: XLR cable passes signal but ~20db lower

I would second Robert's suggestion. We have an install panel where I work and it just recently began to kill signal. I have only been able to isolate so far, but it seems to be something to do with the wiring behind the panel. If I ventured a guess, you and I are in the same boat, Matt.
 
Re: XLR cable passes signal but ~20db lower

I bought a cable (can't remember the brand) that had a connector that lit up with an led when phantom was present. I thought it would be great for my Smaart rig because I could see where the mic was when it was dark. The light worked great; not too bright but if you were looking for it from 25 feet away in a dark room you could see that it was there.

However, the spl calibration on my rig was WAY off! I couldn't say exactly how much it reduced the signal, but I would guess about 15 db.

A thought on your cable, beyond the corrosion possibility: Maybe the female connectors are stretched out just right so they barely make a connection. I'm sure you would have wiggled the connectors though, that should show the problem.

Have you opened up the connectors? Maybe someone built it with some resistors to use as an inline pad.
 
Re: XLR cable passes signal but ~20db lower

Bennett Prescott said:
Wouldn't this be 6dB?
Click to expand...

Drew replied with a concise reply while I was re-typing my response after a power outage ate mine.

Generally, loosing pin 2 or 3 would result in a 6 dB loss only if the output and input device are using pin 1 as part of the audio circuit.
The OP was using a phantom powered DI, the resistors in series between pins 2 and 3 and the voltage source vary in both the mixer and the DI, which can result in differing attenuation amounts when pin 2 or 3 go open. Even using dynamic mics, loosing pin 2 or 3 is likely to result in more attenuation than 6 dB. Depending on capsule sensitivity and transformer winding ratios and wiring, the range could go from a minimum of -6, and often as much as -60 dB or more, which usually just makes one discard the cable, rather than going for make up gain. However, with board operators not experienced with "normal" levels for mics and console input settings, plenty of times I have experienced when loosing pin 2 or 3 resulted in not using a 20 dB input pad, when the intermittent connection connection comes in on a drum hit, or a loud bass note, yikes, I hate it when that happens…

Art
 
Re: XLR cable passes signal but ~20db lower

If you have pin 1 open, the (active?) DI does not get phantom power. This will disable the amplifier/buffer in the DI, though it might still leak a little bit of signal through. The cable might still work fine on a dynamic mic. Check the soldering in the connectors. If there's nothing visible, put it in the garbage can ;-)
 
Re: XLR cable passes signal but ~20db lower

While generally we expect a neat 6dB drop or perhaps complete loss if one leg is open, but I can imagine another hypothetical.

Imagine if there is a resistor termination inside the receiving input circuitry directly between pins 2 and 3. When both 2 and 3 are connected and driven from low impedance all is well, but now if one or the other leg is open we get a single legged full input on the connected input, but now the opposite polarity input is being fed through the input termination. In general there will be another resistance to ground on both inputs, so this opposite polarity signal is slightly padded down so it doesn't subtract completely. A 1 dB loss to the subtracted opposite signal will give about -20 dB result.

Caveat lector... this is just a WAG hypothetical. but it could happen.

A cable tester should reveal the issue... Note: Pin 2 and 3 shorted should give complete cancellation, but in an imperfect world, it could also just attenuate the signal a bunch.

Fix the cable with an axe...

JR
 
Re: XLR cable passes signal but ~20db lower

I had a different (but possibly related) cable problem that baffled me much longer than it should have. I had connected an unbalanced source (consumer CD player) to a balanced line level input through some ugly combination of cables and adapters, some of which, no doubt, dated to the 1970s.

I fired it up and the sound was clear and loud, and VERY bright. After listening for a bit I concluded that there was no audible bass whatsoever, but otherwise it sounded fine. What was wrong?

It turns out that I had ground continuity but the CD player output ended up on one conductor of a shielded twisted pair and one side of the balanced input on the other, with no continuity between the two. So I had made a nice capacitor with one wire as each plate and, in combination with the load impedance, the resulting first order high-pass filter must have had a -3dB of around 500 Hz. Doh!

-F
 
Re: XLR cable passes signal but ~20db lower

Ben Lawrence said:
I know you probably checked but since you didn't mention it. Those do have a 20db pad. It happened to me this last weekend. Hunting for a problem pad was engaged.
Click to expand...

I haven't given the cable any attention since the gig.... The PAD was not engaged on the DI, that was the first thing I checked. I even unplugged and replugged the cables a couple times before swapping it out.
 
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