[makkan00]

Originally Posted by doughboy

Yes, Balanced in these terms has nothing to do with audio or EQ, its a term to describe the signalling layout.

+1

Differential signal is something which is against the normal amp. Most of the amps cannot take differential signals and hence you need to use something which converts differential signals to normal one.

[BigBanana]

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.

An RCA type plug has only two connections. The outer connection is usually 0V ground (screen connection or 'earth').

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.


Amplifier diagram of one channel.


A convertor of some description is required.

The most simple of which is the audio bal-unbal transformer.

This can be connected simply as in the second diagram, if the new power amplifier input level is rated for speaker outputs. (They usually have input level adjustment control).

The two centre connections on the transformer shown are not used.
The 22 ohm resistor (R shown on the diagram) is there to provide some load for the existing amplifier because its speaker will no longer be connected.

(Two of these will be required for a stereo amplifier).


Transformer diagram

[doughboy]

Bigbanana, nice diagrams!

I think the OP was talking about low level HU outputs rather than amplified ones though?

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.

Either, for low cost, you use a 2 wire connection with one grounded as ground continuity and signal wire in one. (i.e. RCA)

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.

Agree on you isol diagram, just needs a grounding connection shown from the RCA outer portion

[BigBanana]

Hehe.
The diagrams came out a bit bigger than I was expecting....

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).

I don't think the standard head unit has line level outputs, or does it?

(PS. the THA is available for sale with a loom).

[parapaul]

Originally Posted by BigBanana

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.

Originally Posted by BigBanana

An RCA type plug has only two connections. The outer connection is usually 0V ground (screen connection or 'earth').

Correct.

Originally Posted by BigBanana

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:

Originally Posted by BigBanana

the new power amplifier input level is rated for speaker outputs. (They usually have input level adjustment control).

Originally Posted by doughboy

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.

Originally Posted by doughboy

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...

Originally Posted by doughboy

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...

Originally Posted by doughboy

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.

Originally Posted by BigBanana

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.

Originally Posted by BigBanana

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.

[mistryn]

[QUOTE]

=parapaul;12824895]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.

QUOTE]

This is quite interesting to read as I am in a similar boat as I plan to use a wiring harness behind the HU with the HU coded to HiFi. I am/was under the impression you can only use certain amps that accept differential balanced inputs otherwsie suffer from a loit of noise - this puts me way off my budget for amps.

As all i wanted to do was feed a bit more power to the speakers/subs without spending too much. But when you look at amps that accept diff balanced inputs they are in the region of £350+

[BigBanana]

Originally Posted by parapaul

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.


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.

Assumption:
The coding changes the way the speaker outputs are driven; into a single ended configuration. IE. One pair of output transistors are no longer driven.

Then.
I would say technically, it would be possible to directly connect the RCA plug as long as you know which of the original speaker connections remains as 'live' and which one is now 'earth'.

I would be inclined to connect the 'earthy' side to the RCA plug outer via a low value 2Watt resistor. (Any standard value in the range 22 to 47ohm). That way, if anything untoward happens, the output stage transistors won't get fried.....

You may still need a loading resistor on the speaker output but it all depends on the HU internal circuit.

It shouldn't cause a problem if you do fit them.

::

[makkan00]

I have been there and I have done all sort of experiments.

I started with normal JBL amplifier (GTO series which is excellent).
After coding HU (balanced input), and connecting it to standard amp, there was noise due to differential input. I used standard LOC for this and that did not help at all.


I had to add LOC (which converts balanced differential to balance standard signals) to get rid of noise and to be able to use normal amp with differential BMW HU output.

Lately, I've moved to JL amp which accepts differntial input and now I don't require LOC.
HU---> JL Amp ---> Components and I must say, sound quality is way better than previous JBL and Kenwood amp which I tried earlier.

[mistryn]

Sam what LOC did you use?

[BigBanana]

PS.

You can still use the bal-unbal transformers suggested, exactly as shown above. They work with any level.

At low level, they would perhaps be best mounted in a metal box. There is no problem with 'mains hum' pickup in a car, but there will still be electrical noise from other components. Pickup can be reduced by using screened cable, which RCA connectors were designed for.

[parapaul]

Originally Posted by makkan00

I have been there and I have done all sort of experiments.

I started with normal JBL amplifier (GTO series which is excellent).
After coding HU (balanced input), and connecting it to standard amp, there was noise due to differential input. I used standard LOC for this and that did not help at all.


I had to add LOC (which converts balanced differential to balance standard signals) to get rid of noise and to be able to use normal amp with differential BMW HU output.

2 questions Sam:

1. With the JBL amp you tried, was that with RCA connectors straight onto the speaker wires, or did it have speaker level connections?

2. Which LOC did you use in the end?

[makkan00]

Originally Posted by mistryn

Sam what LOC did you use?

Originally Posted by parapaul

2 questions Sam:

1. With the JBL amp you tried, was that with RCA connectors straight onto the speaker wires, or did it have speaker level connections?

2. Which LOC did you use in the end?

Sorry guys,
Just read your message.
1- Speaker wires to standard LOC ---> JBL Amp.
I did not try the speaker inputs as JBL amp required 6V-11V speaker level input. Whereas with hi-fi coding max signal is 5V. I would have attracted noise if I would have used speaker level input to JBL amp.
2- As mentioned earlier in this thread, it was 'Ven4' LOC.