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      10-11-2012, 01:06 PM   #27
parapaul
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Quote:
Originally Posted by BigBanana View Post
Looking at the amplifier output diagram, (radio/cd that is already fitted) you can see that neither of the speaker terminals (A and B) are connected to 0V (Car ground connection).
The speakers are connected as shown in the diagram to enable more power to be achieved from a single 12volt supply.
Correct.

Quote:
Originally Posted by BigBanana View Post
An RCA type plug has only two connections. The outer connection is usually 0V ground (screen connection or 'earth').
Correct.

Quote:
Originally Posted by BigBanana View Post
If the input of the additional power amplifier is of the un-balanced type (RCA type plug), it cannot be directly connected to the type of output shown which is typical of a car amplifier output.
Correct. Unless:

Quote:
Originally Posted by BigBanana View Post
the new power amplifier input level is rated for speaker outputs. (They usually have input level adjustment control).
Quote:
Originally Posted by doughboy View Post
I think the OP was talking about low level HU outputs rather than amplified ones though?
I was. Once coded from Professional to HiFi settings, the head unit doesn't output heavily EQ'd speaker level signals, it outputs a flat low level signal.

Quote:
Originally Posted by doughboy View Post
Agree, an amplified output is usually not solidly referred to ground on one pole, as the speaker itself has no need for a ground reference, only signal differential.

However, the low-level signals need a reference level in order for the signal to have some relative amplitude / phasing between amplifier stages.
Yup. Now, THIS is the question I'm trying to find an answer to: Can I do this...

Quote:
Originally Posted by doughboy View Post
Either, for low cost, you use a 2 wire connection with one grounded as ground continuity and signal wire in one. (i.e. RCA)
And if not, how do I do this...

Quote:
Originally Posted by doughboy View Post
Or for better noise isolation you isolate the A & B wires from ground, and use a 3rd wire/screen as ground to give ground continuity between devices.
Quote:
Originally Posted by BigBanana View Post
I installed a Blaupunkt THA275 in my previous beemer. Although it did have line level inputs, as far as I recall, the wiring loom that connected it to the car just took the standard dash HU speaker outputs for its input. (Hence my attempted diagram).
That's right - the blaupunkt amp has speaker level inputs, hence why it worked.

Quote:
Originally Posted by BigBanana View Post
I don't think the standard head unit has line level outputs, or does it?
No, but once coded to HiFi settings, it does.

As an aside, I had an email from Car Audio Direct - who really know their stuff - and they suggest that the JL XD amps are no different to any other amp. Once an RCA connection is made, the line becomes unbalanced.

Still trying to find out if I can just solder an RCA to the end of the speaker wires or whether I need to ground the sleeve.
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