Amp to cab cable question

[Richard R]

I have been given a very early Asdown ABM C300-100 combo, with a 15" extension cab. I need a cable to go between the amp and the extension cab. 

A quick email to Ashtons provided a full set of specs, drawings and a manual, and a recommendation of a cable rated to 200W. The rating was given as 200W, but not a current rating.

 

It's jack plugs at either end, and my question is this:   I have high quality jack plugs, and flexible 13A mains cable. Is there any reason I can't make up my own lead? 

 

 

[chyc]

26 minutes ago, Richard R said:

It's jack plugs at either end, and my question is this:   I have high quality jack plugs, and flexible 13A mains cable. Is there any reason I can't make up my own lead?

On a practical level, mains cable will not be as flexible as dedicated speaker cable but if treated right I would happily use repurposed mains cable (and I have done, albeit internal to a cabinet). It's not going to be melting the wire. For reference, a 13A mains cable will happily take multiple kW of power.

 

Using the cable as a guitar lead will not work out so well as the cable will be unshielded so you'll get a lot of unwanted interference added to your signal so bear that in mind if you want the cable for double duty.

[jezzaboy]

You can buy a decent speaker cable for £15 or so, I wouldn`t be faffing about with a mains cable. Better off with the right thing?

[Richard R]

It's not flat twin-and-earth, it's mains cable from an appliance- should be flexible enough.

 

The amps rating is relevant - 200W at 20V is 10A. That would melt a 3A cable which at 250V would handle well over 500W.

[Richard R]

1 minute ago, jezzaboy said:

You can buy a decent speaker cable for £15 or so, I wouldn`t be faffing about with a mains cable. Better off with the right thing?

 

True, but I have the cable and connectors sat in the garage.

 

[tauzero]

8 ohm cab? Power = I^2 * R, substituting known values 200 = I^2 * 8 (assuming it's an 8 ohm cab) so I^2 = 12.5, so the current is about 3.5A.

[tauzero]

And all my jack-jack speaker cables are 2-core flexible mains cable.

[chyc]

3 minutes ago, Richard R said:

The amps rating is relevant - 200W at 20V is 10A. That would melt a 3A cable which at 250V would handle well over 500W.

The voltage drop you need to worry about is from one end of the cable to the other. Tauzero's power equation is what you need, and you need to measure the resistence of the wire but trust me 13A is plenty, the resistence of the wire will be tiny, orders of magnitude lower than the resistence of the cabinet.

[Downunderwonder]

13A mains cable is way more than required. You could run a space heater at 5m on it.

 

Your biggest hassle is going to he soldering the big wire onto your plugs, and hoping the strain relief holds.

[Richard R]

I had worried about the size of the wires onto the terminals.

I may have some 5A wire somewhere.  I shall have a look and report back.

[Richard R]

9 hours ago, tauzero said:

8 ohm cab? Power = I^2 * R, substituting known values 200 = I^2 * 8 (assuming it's an 8 ohm cab) so I^2 = 12.5, so the current is about 3.5A.

 

👍

I had forgotten that I had the resistance of the cab as another known quantity and so the current could be calculated.

 

I wondered why anyone would quote a cable rating in W not A, but I guess it's easier to read the amp specs which quote power into a given speaker and buy a cable to match the power.

Which is of course @jezzaboy's very sensible suggestion 😀

 

[Bill Fitzmaurice]

3 hours ago, Richard R said:

I wondered why anyone would quote a cable rating in W not A 

 

Because both amp and speaker ratings are written by marketing departments, not engineering departments. Watts sell gear, amperes and volts don't. Wire capacity ratings come from engineering departments.