Will splitting RCA's drop the HU voltage output?

[Flipx99 5,000+ posts]

The guys over at DIYMA said you do need a line driver if you use a Y adapter to split a signal.

I was considering this going 3way hydrid-active front stage. They said if you split the "high" into a midrange/tweeter, you would need a line driver to keep the voltage up.

However, your battery anology does make sense as well.

It couldn't hurt to add a line driver either way.

 

[inapontiac 10+ year member]

with my limitted experience and with the hifonics brutus line, daisy chaining actually decreased the output and the method i used was cut off the end of the RCA comming from the headunit and (keep in mind, im running the ones from the headunit to 4 amps so y-splitters would have been everywhere) i had 4 RCAs and cut one end off each of those and connected the wires together almost in a ball and electrical taped them and no problems since.. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[n2audio 5,000+ posts]

The guys over at DIYMA said you do need a line driver if you use a Y adapter to split a signal.

they're either stupid, or trying to sell line drivers.

hopefully the latter.

It couldn't hurt to add a line driver either way.

if the HU is of decent quality and has 4v+ pre-outs it would be pointless IMO. Add any electronic component to the signal path some level of noise will come with it, and the purpose has been defeated.

 

[bangandow 10+ year member]

thylantyr - what math are you doing? I'm not following why an amp with more input impedance would reduce the HU voltage more than an amp with less input impedance?

Agreed... it seems like it would be the other way around... please explain

Well, if the voltage isn't being halved, then how else could my incredibly high gains be explained, given the fact that the pioneer 7800 has a claimed preout of 5v -IIRC-.

As always, thanks for your help... I'll try to get my hands on a multimeter at some point today and maybe I can bring some real numbers to the table...

 

[bangandow 10+ year member]

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.

//content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif

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.

I don't understand why a greater impedance at the amp and a lower output impedance at the HU is a good thing... I would think that a greater impedance at the amp would drop the voltage, no? Why isn't it an inverse relationship?

 

[n2audio 5,000+ posts]

Well, if the voltage isn't being halved, then how else could my incredibly high gains be explained, given the fact that the pioneer 7800 has a claimed preout of 5v -IIRC-.

differences in ratings

//content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif

 

[bangandow 10+ year member]

Before this, I had 4 RCAs running to 4 channels on the amp and the gains were set less than midway... now I have 2 RCA's being split into 4 before the amp, and the amped bridged down to two channels, and the gains are very high to get a similar volume.

I've been using the same equipment the whole time, just wired differently, so I don't think differences in ratings would account for it.

 

[zukiaudio]

http://www.millionbuy.com/paupld6.html

 

[thylantyr 10+ year member]

thylantyr - what math are you doing? I'm not following why an amp with more input impedance would reduce the HU voltage more than an amp with less input impedance?

Source output impedance and load impedance are part of the formula to find the loading effects.

Here's the math (calculator I linked in post #5.)

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.

 

[zukiaudio]

i also have seen where people use multiple tube amplifiers in a bi-amp/wire set up. and lost volume/gain. so they modified the rca cables with a series resistor of different values (try different ones and listen til find one they like)just before the cable went into the amplifers. to restore the lost volume/gain.

i believe the main reason for gear having high impedances is to reject hum.

 

[thylantyr 10+ year member]

I don't understand why a greater impedance at the amp and a lower output impedance at the HU is a good thing... I would think that a greater impedance at the amp would drop the voltage, no? Why isn't it an inverse relationship?

Here's the ideal situation. An amplifier with a lower input impedance has

potential to have less noise induced. Resistors themselves, have noise specs.

If you made an ampliifer with 1 megaohm input impedance, it's easier to

manifest noise than if the amp was design with a lower impedance. The designer has to choose the sweet spot for the design. I would say that 10k - 47k ohms

is a very good range, less is best.

But if the amplifer input impedance is too low, it wll drag down the source

voltage due to the relationship between source and load impedance as

seen in the 'math post'.

If you were to build an amp with 10k input impedance and a HU

with 10k output impedance, your HU voltage is 1/2 by the time the

amp 'see's it. This isn't ideal either.

If you reduce HU output impedance from 10k ohms to 100 ohms,

the voltage drop is much less.

If you are designing your own source and amp, try to keep the

amp input impedance at least 10x higher than the source output impedance

so you have only a 10% loss. You can go higher than 10x, but not craZy high.

 

[n2audio 5,000+ posts]

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.

Which is a small enough variation that very few (none at all?) amp gain dials will be precise enough to adjust for .17v.

I appreciate the math, but the answer is still no - it doesn't "split" the voltage, and unless you're splitting it 4, 5, 10? times it's not changing enough to be of any concern.

 

[Justintoxicated 10+ year member]

Which is a small enough variation that very few (none at all?) amp gain dials will be precise enough to adjust for .17v.
I appreciate the math, but the answer is still no - it doesn't "split" the voltage, and unless you're splitting it 4, 5, 10? times it's not changing enough to be of any concern.

Well you might only be getting a slight voltage drop but the overall power reaching the amps may be significantly lower, maybe not. I think it will depend on the HU. I would imagine a low impedence HU would be able to supply more current to the RCA's than a HU with a high impedence.

 

[bangandow 10+ year member]

Well the fact still remains that I'm having to set my gains much higher now that I've split the RCA's... maybe my hypothesis was incorrect, but the problem still stands //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

Thanks for all the help

 

[squeak9798 5,000+ posts]

When you split a cable off your cars battery the VOLTAGE is not changed but the maximum Current through the split cable is (which can affect voltage since it is coming from a battery). If you split some 0ga wire into 2, 0ga wires then your limiting the current at the split, you will be limited to the current of the original 0ga wire, so the wire after the split may as well be smaller gauge since they will only have 1/2 their typical current capabilities.

Doesn't really have much to do with the topic of "splitting the voltage".

At the preamp level the current levels are extremely minute. For a single y-splitter, the headunit should have sufficient abilities to supply the necessary current and all of the wires will have sufficient abilities to carry the current.

Since you can run 30ga wire to your amp and get 14.8V to it without issues does not mean the amp is receiving enough power since you would horrifically be limiting the current.

Not really related to the topic either.

Now I know for a fact TV signals degrade quite quickly when splitting the cables. Go to best buy, and look at their TV's that are all split off a single set of cables (In Parallel) some of them may look like *** even though they are quite good. This is because the signal is split too many times. You can't judge the TV set by the way it looks at Best Buy.

We aren't talking about using dozens of y-splitters, we are talking about using one.

Yes, I would advise again using a large quantity of y-splitters. At that point, it's definitely time to add some line drivers (or rethink your system layout).

But for a single y-splitter per line, the effects are inconsequential.

So I guess I don't understand how RCA's would be any different.

Basic electrical laws.

Are they Magic?

Depends on which audiophile you talk to //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

(joke because most "audiophiles" like to pretend as though signal cables have some mythical properties)

I thought audio signals were sine waves?

They aren't necessarily all perfect "sinewaves"....but yeah, it's all analog.

Again the voltage drop may not be significant, but the signal strength itself after the load can't be as strong can it?

While voltage stays the same (minus the tenth or so of a voltage noted earlier) and is identical at each input, current doubles and is split between them. The current flowing through the RCA's is extremely miniscule...small enough that the headunit can supply ample current and the wire can carry ample current...so the effect is again negligible.

Please explain how this is any different.

Does it make any sense yet?