Voltage drop over my rca's

Mithrandir · Post by **Mithrandir** » Thu Apr 28, 2005 8:58 am

My RCA wires are 1.5 ohms of resistance, how much of a voltage drop could that cause from the head unit to the amp?.

William from NOLA · Post by **William from NOLA** » Thu Apr 28, 2005 9:18 am

You'll need to know the amperage coming down the RCA to get an answer.

Assuming the amperage is .4 amps with the 1.5 ohms, your voltage down at the end of the RCA should be down .6 volts

V = IR

V= voltage
I= inductance (amps)
R= resistence (ohms)

spkrman · Post by **spkrman** » Thu Apr 28, 2005 10:10 am

what sort of RCA's are these?

William from NOLA · Post by **William from NOLA** » Thu Apr 28, 2005 10:20 am

He measured the resistence in his RCA's is what he means.

spkrman · Post by **spkrman** » Thu Apr 28, 2005 10:28 am

William from NOLA wrote:He measured the resistence in his RCA's is what he means.

ohh... so these aren't dual 1.5 RCA sobm00fers

William from NOLA · Post by **William from NOLA** » Thu Apr 28, 2005 10:39 am

lol, well you never know knowing mith :)

Nah, I was talking to him about his cousins Sony crap and why his gain is up all the way to where it baffles him that it hasn't blown up yet. I've come to the conclusion that his RCA's have so much resistance that the gain HAS to be up that high just to match it!

Fishy · Post by **Fishy** » Thu Apr 28, 2005 5:43 pm

Look at the input impedance of the amp. I think 22 kohm is a good ballpark figure. Thats what Harrison Labs assumed when designing their Fmods:

http://www.hlabs.com/technical/crossovers/page2.html

1.5 ohms is pretty negligible in comparison. In other words for 4v preouts the current would be given as 4/22001.5 or .182 milliamps. The voltage drop over that 1.5 ohms of RCA would be (.182x10^-3)(1.5) or .27 mV. Not a lot.

Every amplifier is different and I think the input impedance also varies according to what you have the "gains" at as well. This is one of the reasons I'm not a big fan of Fmods. A 20 Hz subsonic filter Fmod does not really have a 20 Hz crossover point in all applications.

At least this is the way I understand it.

-Fishy

spkrman · Post by **spkrman** » Thu Apr 28, 2005 10:00 pm

i cant see 1.5 ohms over what, 20 feet of wire being "acceptable"... thats gotta be some thin thin wire.

Jszar · Post by **Jszar** » Thu Apr 28, 2005 11:35 pm

spkrman wrote:i cant see 1.5 ohms over what, 20 feet of wire being "acceptable"... thats gotta be some thin thin wire.

if he measured it at 1.5 ohms, then it's 1.5 ohms, you can't debate that. i really am not even sure what you are saying or commenting on.

spkrman · Post by **spkrman** » Thu Apr 28, 2005 11:49 pm

i'm not debating? If it was measured.. thats what it was measured.

I'm just saying those must be some crappy wires to read that much of a resistance, or a bad meter.