Patch cables sound like ass

general questions, comments and ideas about recording, audio, music, etc.
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Patch cables sound like ass

Post by gyrofrog.com » Tue Oct 12, 2004 10:09 pm

Howdy,

I put together a few patch cables (1 conductor, 1 shield; TS connectors) and all but one of them add a nasty hum to the sound.

I've checked for shorts between the conductor and ground - everything's OK (to the extent that I can try flexing the cable in one hand and hold the multimeter in the other).

My understanding is that the ground shield should only be soldered at one end, so as not to cause a ground loop. I tried soldering to ground at both ends anyway, and the hum was eliminated.

I wonder if the ground braid is messed up and has openings along the length of the cable (and thus soldering at both ends helped the sound). If so then this is the case with three different batches of raw cable.

I'm not sure what I did differently with the one cable that worked. It is still grounded at only one end.

Anything else painfully obvious that I should look for?

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Re: Patch cables sound like ass

Post by I'm Painting Again » Tue Oct 12, 2004 10:39 pm

connecting the shield on both sides is correct on TS i's to TS o's i think..you leave the shield disconnected if you are going from balanced to unbalanced..like bal xlr to unbal TS or something..


http://www.vandenhul.com/artpap/wiring21.htm

heres a diagram..

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Re: Patch cables sound like ass

Post by gyrofrog.com » Wed Oct 13, 2004 9:45 am

BEARD_OF_BEES wrote:connecting the shield on both sides is correct on TS i's to TS o's i think...
Thanx for that (I bookmarked the link). I have a Craig Anderton book and some guitar-wiring instructions that say otherwise, but that got me where I am (see subject line). Grounding both ends sounds better, at least for the equipment I've got sitting around here...
Last edited by gyrofrog.com on Wed Oct 13, 2004 9:54 am, edited 2 times in total.

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Re: Patch cables sound like ass

Post by stuntbutt » Wed Oct 13, 2004 9:47 am

By "patch cable" do you mean a cable used to patch points on a patchbay or a cable to go between equipment? The grounding technique of only connecting the "out" only applies to cabling betwen devices. A patchbay is not a device. Also, I am not sure it is good practice with unbalanced lines. Death to groundloops!

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Re: Patch cables sound like ass

Post by gyrofrog.com » Wed Oct 13, 2004 9:53 am

stuntbutt wrote:By "patch cable" do you mean a cable used to patch points on a patchbay or a cable to go between equipment?
The latter (i.e. organ to mixer). Uh-oh!

Where else should I look to eliminate the hum?

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Re: Patch cables sound like ass

Post by Family Hoof » Wed Oct 13, 2004 10:12 am

The ground (shield) is carrying the negative half of the AC signal in a TS situation. It needs to be connected (both ends!) to properly pass signal.

Ever notice when you use a bad speaker or instrument cable in your guitar rig and you get a shitload of hum? It's because the shield connection broke on one side. Fix it!

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Re: Patch cables sound like ass

Post by I'm Painting Again » Wed Oct 13, 2004 10:19 am

gyrofrog.com wrote: Where else should I look to eliminate the hum?
your power supply..you could get an isolation transformer device like this :

http://www.poweruptech.com/tl_hgit.html

tripp-lite hospital grade is what you want

and going from instrument level to line level as in organ to mixer you should have a direct box..that will take noise away..though your cabling might change in this case

http://www.zzounds.com/item--CTYTYPE85

the quality and length of cable will effect noise too..if your using the cheap stuff it can hurt sound quality..

then anything that need to be converted from unbal -10dbv to bal +4db or vice versa could benefit from this :

http://www.avsupplystore.com/lls8.html

its an active transformer circut that comes in 8 channel or 2 channel versions

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Re: Patch cables sound like ass

Post by Mark Alan Miller » Thu Oct 14, 2004 6:41 am

Agreed. Both conductors must be soldered at both ends of any patch (bay) cable. Balanced or unbalanced.
he took a duck in the face at two and hundred fifty knots.

http://www.radio-valkyrie.com/ao/aoindex.htm - download the new record (free is an option!) or get it on CD.

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Re: Patch cables sound like ass

Post by Family Hoof » Thu Oct 14, 2004 10:02 am

cowtrax wrote:Agreed. Both conductors must be soldered at both ends of any patch (bay) cable. Balanced or unbalanced.
Damned right! This is a FACT, not an opinion. Physics!

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Re: Patch cables sound like ass

Post by stuntbutt » Thu Oct 14, 2004 12:52 pm

I don't know guys, I think it is pretty common to only connect the shield at one end of a balanced line. All 3 studios where I do sessions, as well as my home rig and the club that I do FOH are wired that way. I don't know much about electronics, but I believe that for audio you only need/want one path to ground. This only applies to the interconnect of devices that are powered. I learned it from working on a wiring crew for a studio that was built from the ground up and hired a "wiring designer".

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Re: Patch cables sound like ass

Post by I'm Painting Again » Thu Oct 14, 2004 1:23 pm

I believe hes doing unbalanced wiring not balanced..

I've never heard of TS-TS (single core cable- I'm assuming hes using single core) wired any other way..

it true that balanced lines should be wired with one end of the shield disconnected but only on line level interconnections when the gear is not properly grounded..and if there is RF in the location the shield should be connected at both ends..and then mic cables need both ends connected always..condenser mics use the shield for phantom power..

his example of organ output to mixer..reveals at least one thing hes wiring has an unbalanced output..whether the mixer has an unbal or bal input is not known..there is only so much you can do when the situation is not described fully..

there are proper ways to wire different gear together..its confusing..there are 3 or 4 different ways you can wire bal to unbal gear depending on the output stage of the bal gear your wiring from..

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Re: Patch cables sound like ass

Post by gyrofrog.com » Thu Oct 14, 2004 4:26 pm

BEARD_OF_BEES wrote: his example of organ output to mixer..reveals at least one thing hes wiring has an unbalanced output..whether the mixer has an unbal or bal input is not known..
It's a Mackie 1202, and the input says "Bal or Unbal." But I still get the hum if I run the cord to an amp instead (i.e. until I soldered both ends).

I was having the problem with both single-core and double-core lines, unless and until I soldered the shield to both ends. (I'm using the double-core with either TS or TRS plugs (not on the same cable). In the case of the TS plugs I soldered both the second conductor and the shield to ground at one end; later I soldered the shield only to the other end and it was OK)

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Re: Patch cables sound like ass

Post by I'm Painting Again » Thu Oct 14, 2004 7:45 pm

im not sure if you went up a step in the link i posted but everything you need to know about how to wire is spelled out in this chart :

http://www.vandenhul.com/artpap/wiring.htm

for the 1202 wire anything from an unbalanced source TS-TS shield to shield tip to tip..

for any balanced gear it would be TRS-TRS (*first try everything connected, then try disconnecting the shield to see whats less noisey)..or XLR-XLR (*same deal) or XLR-TRS/TRS-XLR (*same deal)..

on an XLR

1 is shield
and
2 is typically hot on modern equipment
some older stuff 3 is hot

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