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Voltage drop over my rca's
Posted: Thu Apr 28, 2005 8:58 am
by Mithrandir
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?.
Posted: Thu Apr 28, 2005 9:18 am
by William from NOLA
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)
Posted: Thu Apr 28, 2005 10:10 am
by spkrman
what sort of RCA's are these?
Posted: Thu Apr 28, 2005 10:20 am
by William from NOLA
He measured the resistence in his RCA's is what he means.
Posted: Thu Apr 28, 2005 10:28 am
by spkrman
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
Posted: Thu Apr 28, 2005 10:39 am
by William from NOLA
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!
Posted: Thu Apr 28, 2005 5:43 pm
by Fishy
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
Posted: Thu Apr 28, 2005 10:00 pm
by spkrman
i cant see 1.5 ohms over what, 20 feet of wire being "acceptable"... thats gotta be some thin thin wire.
Posted: Thu Apr 28, 2005 11:35 pm
by Jszar
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.
Posted: Thu Apr 28, 2005 11:49 pm
by spkrman
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.