Did I goof my cable?

Calling all techies...
I recently made up a cat5e cable very similar to the FFRC on the TNT-Audio website, to run from a NAD 3240PE amp.

3 runs of cat5e per cable, positives of two for pos woofer, negatives of two for neg woofer, pos and negs split in 3rd run for tweeter. All sweet and easy.

DIFFERENCES were:

BRAIDED the three runs, made each cable 8 METRES long, used 'standard' CAT5E cable (TIA/EIA 568B)

On first use they sounded sweet, but after about 30 secs I turned them up and my amp literally smoked... and gave that acrid fried plastic smell. Needless to say it then stopped producing any output (but still powers up).

Two questions:
1) What is the most likely cause for this, is there anything about the cable I can test with your average consumers multimeter?
2) Just out of curiosity, I have ordered some 4a and 5a fuses to see if it does still work, but what else am I likely to have destroyed? (and could I learn to fix it as an exercise in electronics?)

Thanks
Phil (living up to the clueless moniker)

 

phil there is one likely option and one not so likely.

option 1. somewhere in the middle of all those cables you mixed one up, just one, not such a immediately catastrophic deal when the amp is low but once you turn it up, kapow. to check this just use a multimeter switched to continuity mode and check each end of each cable against the opposite ends. check + against + -against- and then -against +. id' bet you get a beep for every=which-way, meaning one of your - wires runs through to the + or vice versa.

finding which individual wire it is inside that 'swarm' will be a bitch.

option 2. your arm just doesn't like the LCR of the cable. unlikely unless you run older Naim or NVA gear.


happy hunting.

 

using a dmm set to continuity ...check each conductor to find which one is attached between + and - ....I think thats what sq225917 said ...but I got lost !

it could be as simple as one wire shorting at the speaker ends so thats worth checking too.

I had a similar thing when I built a set of ffrc's too as long as you got to the amp quickly there may not be any lasting damage..

 

Thanks Gentlemen. It appears I have been tried and found guilty of slapdash production standards on my first cat5 cable!
What would I need to check it for eh, it is after all just the same as running a guitar cable, amp/speaker cable,etc and I have wired loads of those. What a muppet!
It took me no more than 2 minutes to test and locate the single errant wire. darn. Thanks for the fresh eyes on this.
The good news is I have now wired up, tested and installed both and as a mark of 'confidence' slapped them in line with the arcam I have borrowed off my father in law!
Anyway, lesson learnt the hard way, fingers crossed that the amp recovers after a fuse transplant ;-)
Cheers.

 

Be very careful, the output transistors may have fried!

 

Very likely, considering the 'acrid fried plastic smell'

 

Phil

Hope your hifi is well and undamaged mate.

This post should stand as a warning of the dangers of trying to DIY cables IMO... it's not for everyone..

 

I have made up some TNT Triple T cables to about 6-7 meters.

http://www.tnt-audio.com/clinica/triple_t_e.html

I neglected to look at the directionality of all the Cat 5 cables, and upon completion, I realised that I had platted some cables in the wrong direction.

They work OK but I cannot help thinking that my mistake is costing me in sound quality.

Does the direction of the Cat 5 cable matter a lot? I am not sure that I am looking forward to replatting them correctly, or unplatting them for that matter,

 

as a manufacturer of test systems for CAT 5 cables I can assure you that there is no directivity, they are designed for data to flow equally well in each direction, and are measured from both ends.

Chris

 

Wire is not directional. Period. The only time a IC is directional is when the gounding or shielding system require directionality.
When you break in a cable the direction is set.



rollo

 

How can both these statements be true?

What do you mean by "when you break in a cable the direction is set"?

 

Good news.

Thanks

 

The direction used dictates the burn in of the least path of resistance. When you run the cable in the direction set that is what becomes its direction. Wire is not directional. Its the direction in which you burn it in that determines the directionality. My take anyway.


rollo

 

Things that make you go "hmmmm...."

 

I think the amplifier must be well and truly burned in.

 

Chris thanks for that insight. Never really bought in to the concept of wire directionality....