Voltage drop over my rca's

[Ryan from Ohio]

When measuring resistance its IMPORTANT to NOT TOUCH THE LEADS WITH YOUR FINGERS.

Just placing one finger on the metal of one lead can give you a false reading.

Just wanted to throw this info out in case you didnt know it...

[Mithrandir]

yeah I kinda figured that so i didnt touch em. Yep they are 1.5 ohms. Got em with my wiring kit from local shop lol.

[Fishy]

How long are those rca's? I just measured a set of el cheapo 12 ft cables and got .7-.8 ohms or about .06 ohms/ft for both signal and ground. If you have 24 ft rca's then 1.5 ohms sounds about right.

I also measured an 18 ft $60 set of 4 way Monster Cables and got a lil better result of around .6 ohms or .033 ohms/ft.

Here's a table that gives resistance per foot for different gauge wires:

http://www.epanorama.net/documents/wiri ... tance.html

.06 ohms/ft corresponds to about 27 gauge.

Just out of curiosity what kind of readings do you get when you touch your multimeter leads together? Although the rca resistances I measured were fairly stable my Micronta(aka Radio Shack) bounces back and forth between 0 and .5 ohms when I short the leads. I'm not exactly sure how accurate most meters are when measuring resistances that low.

Regardless, any voltage drop with 3 ohms or less(round trip, signal+ground) is going to be on the order of millivolts which is pretty negligible.

-Fishy

[Mithrandir]

k, jw, do u measure by putting the meters power to one and ground to the other rca? thats how i did. Its a 100 dollar meter, craftsman auto ranging.

[William from NOLA]

You'd measure both, but at different times; At one end, do either the ring or tip and the same on the other end. Whichever is higher is probably the most resistence it will see.

[spkrman]

How long are those rca's? I just measured a set of el cheapo 12 ft cables and got .7-.8 ohms or about .06 ohms/ft for both signal and ground. If you have 24 ft rca's then 1.5 ohms sounds about right.

I also measured an 18 ft $60 set of 4 way Monster Cables and got a lil better result of around .6 ohms or .033 ohms/ft.

Here's a table that gives resistance per foot for different gauge wires:

http://www.epanorama.net/documents/wiri ... tance.html

.06 ohms/ft corresponds to about 27 gauge.

Just out of curiosity what kind of readings do you get when you touch your multimeter leads together? Although the rca resistances I measured were fairly stable my Micronta(aka Radio Shack) bounces back and forth between 0 and .5 ohms when I short the leads. I'm not exactly sure how accurate most meters are when measuring resistances that low.

Regardless, any voltage drop with 3 ohms or less(round trip, signal+ground) is going to be on the order of millivolts which is pretty negligible.

-Fishy

millivolts is a big deal when you only have 2v preouts. Its also a big deal because thats a loss that really doesn't need to be there.

I find it hard to believe even the "high end" RCA's use such thin wire. Is 16-18ga out of the question for RCA cables????

geez..

[Fishy]

millivolts is a big deal when you only have 2v preouts.

Ok, lets do the calculations for a set of 2v(rms)preouts with a set of rca's which has 1.5 ohms of resistance(we should actually use 3 ohms but I used 1.5 ohms in a previous example with 4v preouts).

First lets determine the current for an amplifier with a 22kohm input impedance.

I = V/R

where R = 22000 + 1.5

V = 2v

=> I = .091 mA

Now the voltage drop across a resistor is given by

V = I*R

=> V = (.091x10^-3)(1.5) = .137 mV

which just happens to be about half what was calculated for 4v preouts(.27 mV).

The total % drop is 100*(.137x10^-3)/2 = .00685%

The % drop for 4 volt preouts just happens to be about the same.

So as long as the rca resistance is much less than the input impedance of the amp the % voltage drop is about equal regardless of preout voltage and is also INSIGNIFICANT.

If normally you weigh 200 lbs and woke up one morning to find you weighed less than 1/4 ounce more would you care?

I know I wouldn't.

-Fishy

[Fishy]

This is stupid.

If your rca's resistance is only 1.5 ohms you're fine Mith.

-Fishy

[spkrman]

This is stupid.

If your rca's resistance is only 1.5 ohms you're fine Mith.

-Fishy

perhaps its me... but this just seems excessive.

Larger wire would seem to work better... where is that % of drop goin? Where is it comin from?

Would larger wires not "sound better"... particularly if you want to argue that you can hear the difference between amps beyond when they are toward the limits.

[Fishy]

You have to remember that this 1.5 ohms of resistance is in series with the 22000 ohm input impedance of the amp. To be honest I'm not sure I fully understand what role input impedance has to play in this situation, but I do know that if you tried powering a sub using those rca's as speaker wire it'd be a vastly different scenario.



Maybe kiki or jonathan could verify that I'm on the right track here.

-Fishy