Building a Guitar isolation cabinet: How long of a cable?

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alexdingley
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Building a Guitar isolation cabinet: How long of a cable?

Post by alexdingley » Wed Sep 02, 2015 8:47 pm

I'm moving into my new house, and my music space will be the 2nd floor. I found a nice large chase that will allow me to run cables down to the basement with ease. I've been thinking about setting up a wooden crate to hold my guitar cabinet... so that I can really crank it up and mic it with isolation & without being a bad neighbor. I'm just dying to setup that isolated amp area so that I can really crank up the rig (for re-amping / playing) and hit my ribbon mics with plenty of db's.

My question: If I wanted to just place the actual speaker cabinet in the basement... can I cleanly run the head from the 2nd floor, and have a cable running from head-to-cabinet over about 30+ feet, to the basement?

I'm not sure if that's going to be detrimental to the tone, or if a 30+ foot unbalanced, amplified signal line is just begging for outside interference.

Thoughts? Is this the right/wrong forum for this question?

PS: point of interest ??this is a Backstar 5w head and the 10" speaker cabs. Although my regular guitarist would also want to run his Marshal head/cab the same way if it works over that distance.

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Post by Nick Sevilla » Wed Sep 02, 2015 10:54 pm

I tend to stay away from unshielded speaker cable runs longer than 15 feet.

I also tend to stay away from recording loud sound sources with a ribbon microphone.

If you must have your head separated from the speaker cabinets...

http://peavey.com/support/technotes/sou ... gcable.cfm

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Post by dfuruta » Thu Sep 03, 2015 5:49 am

Interference seems unlikely to be a problem due to the high level and low impedance involved. The output impedance of the amp is low enough it'd take quite a bit of capacitance to have an audible effect on tone.

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Post by Drone » Thu Sep 03, 2015 6:41 am

My biggest fear wouldn't be interference on the cable signal, but the impact of the cable on the amp. If you are using a tube amp, you don't want to use a super long cable, as the tube amp is impedance sensitive. If the amp is solid state, go for it, and have fun.

If it is a tube amp, I'd use super thick cable, and make sure the cab was wired for 16 ohm to minimize the losses.
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Post by Injured Ear » Thu Sep 03, 2015 6:46 am

If you were to run unbalanced high impedance guitar level signal, you would be likely to introduce noise and loss.

You're not going to have interference, you'll have signal loss as Nick points out.

You've got to weigh your options
Purist: It affects your tone, puts a different resistance (affects impedance) on your head.
Realist: Does it sound better cranked through 50' of cable than quietly through 10' of cable?

Not to get in a pissing match with Nick, I've done it with low gauge (thicker) speaker cable in the studio plenty of times. It works. Plus getting the amp away from you allows you to hear what's actually coming through the mic more clearly which also improves your recording.
Last edited by Injured Ear on Thu Sep 03, 2015 6:49 am, edited 1 time in total.

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Post by A.David.MacKinnon » Thu Sep 03, 2015 6:48 am

I wired a friend's studio a few years ago and in addition to running mic lines to every room we ran speaker cables too. I think the longest run would be about 100'. We've run lots of tube amps through that with no issues (sonic or damage to the head).

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Post by Drone » Thu Sep 03, 2015 7:24 am

...and contrarily, I've replaced a lot of output transformers, from people using guitar cords, busted cords, or using the wrong impedance (or having a blown speaker) in my time. Tube amps are a crapshoot that way, roll the die only if you are willing to spend a couple of hundred on a new output transformer and a bit more on tech time.

I wouldn't even want to point to a design, or transformer that is more robust than others.
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Post by vvv » Thu Sep 03, 2015 1:34 pm

I'd rather run a long line for guitar to amp (buffer or booster, etc. as needed), and have the amp closer to the cab, me.

That said, and I don't know, would it work to:

Amp/unbalanced line --->DI box---> balanced line --->DI box---> unbalanced line/cab

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Post by The Scum » Thu Sep 03, 2015 4:55 pm

One more voice in the chorus: Use the heaviest gauge speaker cable you can get away with. I wouldn't shield it, because the shielding adds capacitance, and capacitive loads can make amplifier outputs unhappy.
Amp/unbalanced line --->DI box---> balanced line --->DI box---> unbalanced line/cab
If the transformers in the DI can handle the power, it could work. But most DI transformers are spec'd to maybe 1/2 W.
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Post by vvv » Thu Sep 03, 2015 5:35 pm

Yep, I was dumb. A little research says use the heaviest gauge unshielded speaker wire you can - the main prob might be RFI.

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Post by dfuruta » Fri Sep 04, 2015 10:08 am

The problem is not RFI but, potentially, capacitance and resistive losses. Unless your amp is susceptible to picking up interference on its output terminals (which is possible, but you're going to have to try and see) any RFI on the cable itself will be far too low a level to be important.

Resistive losses shouldn't be a huge problem: if you use 12AWG wire, you're looking at under 0.1ohm for your 30' there and your 30' back. If your amp is 5W into 8 ohms (?), you're running 0.8 amps at most - so, your resistive losses in the cabling are I^2 * R = 0.8^2 * 0.1, or 0.064W. This is not a problem.

Capacitance might be a bigger issue, as (like The Scum says) it can screw up amplifier stability. So, it's probably worth looking up the capacitance of the cable you'll be using and picking something low. Or, alternately, run two separate wires instead of one two-conductor cable and keep them a little bit apart from each other - among other things, capacitance between wires depends on proximity...

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Post by dfuruta » Fri Sep 04, 2015 10:11 am

But I don't think you should worry too much. Guitar amps aren't broadband beasts. Try running your amp with a 30' cable, see if it oscillates, and if it doesn't you're probably fine.

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Post by kslight » Fri Sep 04, 2015 10:16 am

I'm not gonna say that a long cable isn't without its problems, but my experience with ISO cabs would suggest that I would be more concerned about the tone difference caused by the limitations of using an ISO cabinet versus that of a speaker cable that's 15 feet longer than what you'd normally use.

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Post by Drone » Sat Sep 05, 2015 6:39 am

I'm reminded of a tale from when I was younger, it may be apocryphal, which was the reason Marshall moved to using 16ohm speaker systems, was that the PA companies at the time were using 18ga wire for hookups and blowing things up :mrgreen:

Running a 30 foot cable, I wouldn't be worried about catching RFI interference, I'd be worried about causing it. I don't know if anyone is familiar with T-Loop systems, but the gist of it is, hearing aids had (or maybe still have) a T setting on them, for use with telephones, whereby the aid would pickup up the electromagnetic emissions from the telephones voice coil, rather than the audio waves. Our local church had a T-Loop, it was a wire that ran round the church, and was driven by an amplifier. Congregants could switch their hearing aid to T and listen without the confusion of echoes they normally had in the church, but it also used to interfere with the amplifier circuit in the old organ in the adjoining hall, which meant you could warp the ministers voice using the volume pedal and effects (yeah my wasted Sunday School years)

So it won't be so bad I imagine, as it will be two conductors side, by side, but be aware that old organ was a good 30 feet from the T-loop too :mrgreen:
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wow! Thanks!!

Post by alexdingley » Tue Sep 08, 2015 6:12 am

Awesome input, everyone!! I love getting a bunch of strong and differing opinions. I'm already using self-made cables from the amp to cabinet, which are pretty heavy duty (will check the gauge later)... but I have no problem making my own super heavy duty cable... the amp has 16ohm & 8ohm outputs... so that will help.

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