Can I use 2 conductor cable for instrument cable?

[LyleCaldwell]

Theoretically I actually agree with you.  In practice, it depends on whether the output device or the input device has the better ground scheme, plus the theory you put forward.  One of the other will make more difference.  Sometimes they combine and you get an ultra-quiet signal.  Sometimes they cancel each other out a bit.

So, we're back to using your ears.  Dammit.   

Please understand, I'm not posting this to be mean-spirited or anything like that...... it's just for the sake of  discussion.  I looked at the references you sent, thought about it, and I'd still put the tied end at the amp...and here is why.

The whole reason for doing this method of cable building is to "drain off" noise..... sort of "intercepting" itt preventing it from ever radiating into the signal pair.  If you connect the tied end at the guitar..... any noise that is picked up on the shield MUST drain somewhere... and the only place it can is at the tied connector...currently plugged into the guitar.  When it does.....it will "hop a ride" back along the signal return wire inside the cable sort of defeating the purpose.   If you plug it in at the amp end the shield will be drained directly to the amp jack ground which, according to theory, will be giving the signal return wire a quieter ride back to the amp.   Just thinking about it.......  in the case of plugging the tied end into the guitar..... that means that any noise that is picked up.... will appear on the signal ground cable... and possibly coupling over to the signal wire depending on the capacitance between the two leads.   If you have a 15 foot cable.... you "sort of" have a 15 foot capacitor.   If you drain it at the amp end.....the noise will hit ground at the amp jack and that will be all.  Less chance of coupling the noise over to the signal cable.    And, with the relatively high impedance of an amp input it doesn't take much to get that noise in to the amp.

The best advice yet is....  try it both ways!   Let your ears be the judge.  Theory is a funny thing sometimes.     Sometimes it works....... sometimes it gets proven ( or at least demonstrated ) NOT to work!!!!  BUt give it a shot becuase the good news is that all you have to do is turn the cable around.  You dont have to rebuild it.   Have fun.

[LyleCaldwell]

Glad it works for you!

Someone else will try it and say "it's too thin."  Such is audio.

When I do this, I use Mogami 2944, which is very low capacitance, so the thinner insulation makes no difference.

[JimRayden]

The single core with earth sounds airier and has a sparkle that the paired cores lacks.

Be careful, some of us are allergical to calling an instrument cable "airy" or "sparkly". Just stick to the expression, "it leaves the highs unattentuated" or "it does lower the capacitance" or "woohee, I got my highs back!"

But, of course, if you wish to be poetic, go ahead.  Everyone will understand you anyway.

------------
Jimbo

[vanessa]

This may sound stupid, but wouldn't running two separate signals next to each other like this create a lot of inductance? Meaning if you tie the two conductors together as one signal line and then ground the shield?

Also making 'semi-balanced' cable it seems like it would make more sense having the shield grounded on the instrument side. Your pickups 'pickup' the signal (and noise) then deliver it to the amp not the other way around. All the noise from the instrument and anything in-between (RFI, EMI etc.) would be drained off before it gets amplified.

[DuncanM]

OK, 6dB per octave rolloff above 14kHz or thereabouts.....

I only notice when I monitor on headphones.

I shall try to be less poetic in future.  

As far as earthing one end of the shield, I'd earth the amplifier end - shortest distance to a solid ground...

[vanessa]

I have to ask again...

Wouldn't running two separate signals next to each other like this create a lot of inductance? Meaning if you tie the two conductors together as one signal line and then ground the shield? Would this also cause a problem with signal quality?

[Processaurus]

I have to ask again...

Wouldn't running two separate signals next to each other like this create a lot of inductance? Meaning if you tie the two conductors together as one signal line and then ground the shield? Would this also cause a problem with signal quality?

An inductor is a coily piece of wire, and a capacitor is metal film or plates stacked close together.  A straight coaxial cable resembles a capacitor much more than an inductor.  If you ran both signal and signal ground through the 2 center conductors you would get more CAPACITANCE, because the signal is now closer to a grounded conductor then it would be with the just the braided shield carrying the ground.  If you have a way of measuring capacitance, it would be illuminating to test the difference in signal to ground capacitance the two cable arrangements we're discussing.  Whether its even a noticeable amount in either case would depend on the brand, and cable length, and any buffering electronics upstream.  It may not make a difference at all, especially because lots of pedals have a small pF capacitor to ground as the first thing the signal hits, as part of an RC network to shunt radio frequencies to ground.

If you use both center conductors carrying the signal, even if they made a tiny inductor by twisting around each other or a tiny capacitor by being close to each other, or both, you are shorting it out by tieing the conductors together at both ends.  Like if you took a coil and soldered a wire across both ends, it no longer has any inductance (no resistance/reactance to high frequencies) , or if you soldered a wire across a capacitor, it no longer has any capacitance (no resistance/reactance to low frequencies).

To be fair, I haven't had a chance to try using a semi balanced cable, mostly because 99% of the noise in a guitar/pedals/amp system seems to come from the electronics and power conditioning than from the cables.  Recently I even used a short unshielded speaker cable as a patch cord (cuz thats what was around) after some buffered pedals and was surprised it didn't add a noticeable amount of noise.  Go figure... 

If you do try it, be sure and tell us what happens.

[LyleCaldwell]

Processaurus,

First, if it seems like I'm picking on you or whatever, I'm not.  We just happen to disagree.

I didn't mean that there would be capacitance between the two conductors.  I mean that the overall capacitance of the cable would increase (up to double).

[DuncanM]

An inductor is a coily piece of wire,

with the emphasis on COILY...
As I understand it, an inductor works by the magnetic coupling of a piece of wire with itself. In a coil, the more turns of wire on the coil the more inductance.
In a STRAIGHT "guitar" cable inductance should be virtually nonexistant as the core couldn't couple with itself (no coiling).

[Nasse]

We have a local component shop at the village and the owner is reaching something about 90 years old and he knows some things about audio and about "doing it in practice" and one of his favorite topics when I try to chat with him is how shitty or cheap you can do it when doing "pro audio". He does some outdoor happening audio and we talked about long cable runs and he sold me few old transformers almost for free, he said I can pay them some day later, no hurry...

What I think I have heard about the topic I think if the impedance is low enough you can sometimes do low level signal with a two conductor cable

[vanessa]

An inductor is a coily piece of wire,

with the emphasis on COILY...
As I understand it, an inductor works by the magnetic coupling of a piece of wire with itself. In a coil, the more turns of wire on the coil the more inductance.
In a STRAIGHT "guitar" cable inductance should be virtually nonexistant as the core couldn't couple with itself (no coiling).

In a straight cable yes, but is not 2 conductor cable twisted or spiraled to combat EMI/RMI? I guess it's design is to run a signal and a ground together, but used with 2 signals, that's where I'm at a loss...

[Peter Snowberg]

The twisted pair of wires along with the use of differential signaling is what combats the interference. It takes both ingredients.

The scheme makes use of the difference in voltage between the two wires rather than between a signal and a ground line.

Let's say that we have two wires sitting at -1 volt and +1 volt relative to ground. The difference between them is 2 volts.

Now if we induce 1 volt of noise in the cable from interference, the two wires are sitting at 0 volts and 2 volts relative to ground. We still have the same 2 volt signal even with an extra volt of noise on the line.