#1




Will splitting RCA's drop the HU voltage output?
I saw this on another forum.... and wondered if its true. I have a Alpine CDA118 that is 10,000 ohm output impeadance at 2V, but i cannot find the input impedance anywhere for my JL amp MD750/1.
Lets take a typical Alpine HU. Lets pick this one. CDA9856 Preout: 2 volts / 10,000 ohm output impedance.. Connect this HU to an Alpine amp with 10,000 ohm input impedance, the voltage is now 1 volt, cut in half. Instead of buying an Alpine amp, you found a good amp with a 47,000 ohm input impedance, the loading effect is minimal, you get 1.95v, much better than 1.0v when you interfaced an Alpine HU to an Alpine amp. I was shocked years ago when I found this. Connect two Alpine amps with splitter, you now have 0.66v. Hint: A good HU will have a 50 ohm  200 ohm output impedance. Even 1000 ohm is ok, but 10,000 ohm is stupid circuit design. Moral of story: Always check equipment specs. One HU & one amp; HU output voltage * (amplifier input impedance / (amplifier input impedance + HU output impedance)). Example. HU preout voltage: 5 volts HU output impedance: 200 ohms Amplifier input impedance: 20,000 ohms. 5 * (20,000 / (20,000 + 200)) = 4.95 volts. One HU & two or more amps Step 1. Find the total parallel impedance of all your amps since the same input signal will be driving all the amp inputs. 1 / (1 / (amp#1 input impedance) + 1 / (amp#2 input impedance) + 1/ (amp#3 input impedance ... etc)) Example: Amp #1 input impedance: 10,000 ohms Amp #2 input impedance: 20,000 ohms Amp #4 input impednace: 47,000 ohms 1 / (1 / (10,000) + 1 / (20,000) + 1/ (47,000)) = 5838 ohms Step 2. Put that 5838 ohms back into the voltage divider formula. HU output voltage * (amplifier input impedance / (amplifier input impedance + HU output impedance)). Example. HU preout voltage: 5 volts HU output impedance: 200 ohms Amplifier #1, #2, #3 parallel input impedance: 5838 ohms. 5 * (5838 / (5838 + 200)) = 4.83 volts. Last edited by craig3972; 02102014 at 04:33 PM. 
Thread Tools  
Display Modes  

