special cable for sub?

gingerjedi

Novice Member
Do i need a special cable to hook up the sub? I have just run speaker cable and soldered an RCA type socket at either end but now i get the dredded hum, even if i unplug the amp out connection i can hear still hear it (it disapears if i unplug from the sub), can the cable generate its own signal?

When looking at ads on the internet the sub cables on offer look like coaxial to me is this what i need?

The sub is a KEF model and the cable length is about 5m.
 

Helicon

Banned
The cable is causing the problem as it has been soldered incorrectly.
 

Dave

Distinguished Member
I may be wrong but i think coax is also shielded to stop this.

You can get a decent quality 5m coax from maplins for 22 quid.
 

Helicon

Banned
Coax isn't the most ideal cable for that purpose, but it'll still work.
 

dingwall

Banned
What is the (most) ideal then helicon?

Any old bit of coax will do, maybe splash out if you still have hum to prevent external interference. In the US, Velodyne used to sell a replacement cable for $5 plus postage for their subs...
 

Helicon

Banned
Normal interconnecting cable, which is usually of a 2 core design. Coax is more suited to digital and picture duties.
 

gingerjedi

Novice Member
The weird thing is the hum almost completely stops when the amp is on, when i switch it off it starts again which in turn stops the sub from auto switching off.

Also is it usual to have the input level on the sub set to between 5-10%? As that is all i seem to need.
 

AngelEyes

Distinguished Member
gingerjedi said:
Also is it usual to have the input level on the sub set to between 5-10%? As that is all i seem to need.

Yes, it will depend what you have the level set to on the amp of course. I think mine is -6db on the Processor and 15-20% on the sub gain. :)
 

Mr Incredible

Distinguished Member
If you are into making your own cable to save a few quid, I took the advice of another site and used a good quality microphone cable and used the twin core wound together as the signal carrier, and the sheaths wound together for ground. I think it only cost me 80p per metre. I have a 12m run and have no problems with hum. The other advantage is that the cable is really flexible so it can be run around skirting board and corners with ease.
 

gingerjedi

Novice Member
I could make my own but am worried that if it doesnt do the job then i have wasted time and money!

Will a standard shielded RCA to RCA cable like you get from musical instrument shops do (£5) or would you recommend a specialist cable such as a QED one?(£35) It has to be thin enough to go under the carpet next to the skirting boards.
 

Helicon

Banned
The QED MSPSW cable is about as thin as you'll get...i'm not aware of any flat ones.
 
R

recruit

Guest
I think the only other cable which is quite flat in design is the Nordost Cinemaflex Bassline Mono cable :thumbsup:
 

PJTX100

Distinguished Member
gingerjedi said:
even if i unplug the amp out connection i can hear still hear it (it disapears if i unplug from the sub), can the cable generate its own signal?
It's probably picking up 50Hz off a mains cable.
 

Mr Incredible

Distinguished Member
PJTX100 said:
It's probably picking up 50Hz off a mains cable.
Which would be best resolved with a well shielded cable.

However, this hum may also be as a result of earth leakage for which there are a number of solutions open to solve. As I have earth leakage protection on my main distribution board using a residual current detector, my "solution" was disconnecting the earth on the sub. No more hum!
 

gingerjedi

Novice Member
gingerjedi said:
I've been doing some digging around and found empiredirect of all places are doing some good deals on the QED's imentioned.

http://www.empiredirect.co.uk/content/products/list~subdept~interconnects~page~4.htm
I posted this about Empiredirect... DONT BOTHER they might be cheap but telling me by email i would have to wait 3 weeks after i've ordered is not on.

I canceled and ordered by phone from hifisuppliers.co.uk who said it would be with me in the morning:thumbsup:
 

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