Floating ground?

[John]

Just bought a new amp to go in my car. Not had to use high level inputs before and reading through the amp instructions, it uses a 'floating ground' so I am not totally sure what I am going to ground the negative speakers wires to (high level input) as it suggests grounding it to the car receiver.

Given where that is , is there another (more convenient) ground which can be used (I'm thinking AWG or something)?

 

[Ted]

From my experience it simply means that the ground of the amp is not at the same potential (i.e. connected) to any other grounds.
This could mean that the internals need to be connected to the amp body and from there to chassis/body ground.

Pretty sure that they want you to ground the amp/head unit etc to the same potential to avoid noise loops.

Either way, it is generally NOT a good idea to ground any speaker wires!

Not in any way an expert but if there is an online manual and you give a linky, I could take a look.

 

[John]

Thanks Ted.

This is the manual:

http://uk.jvc-service.net/webtemp/LVT2205-001A.pdf?CFID=6884989&CFTOKEN=21546917

The very first section 'CAUTIONS AND NOTES' gives the first caveat and then the installation section under 'KS-AX3101D' (bottom right of page 2) is where it next talks about it in the 'B' box...

 

[Ted]

I get a 404 on that link :/

Edit. Found a copy

 

[Starky]

i get a 404 on that link :/

+ 1

 

[Ted]

Ok i think i get it
On many 'normal' systems the 'negative' or common of the speakers is at ground potential and the voltage/current is sourced relative to that.
This means that the common can be connected together and/ or to ground as the common reference point.
On this amp, each output is referenced across the output separately. This means that there is effectively no common reference point and the two 'neegatives'/commons should not be connected together.
Not a problem for you as you will have a pair of wires to each speaker.
On the input side, no such problem. The input is isolated from the output. Bring in the wires from the head unit and it will be ok to join the common s together - make sure that they ARE the common.
Hope i've explained that ok.
Bottom line - nothing to worry about as long as you wire up with two wires between the amp and each speaker as it already will be.
Make sure you phase the speakers correctly

 

[John]

I tried to cut out the click - this should work if required:

Support | JVC United Kingdom

On this amp, each output is referenced across the output separately. This means that there is effectively no common reference point and the two 'neegatives'/commons should not be connected together. Not a problem for you as you will have a pair of wires to each speaker.

OK, so the fact this is a mono amp and I am only wiring up a single sub means that it is still not a problem (correct me if I am wrong!).

On the input side, no such problem. The input is isolated from the output. Bring in the wires from the head unit and it will be ok to join the common s together - make sure that they ARE the common.

OK, the high level input for this is coming from the AGW / Audio GateWay (existing car amp). Is it a fair assumption the grounds will be common, or is it better to get my multimeter out?

Bottom line - nothing to worry about as long as you wire up with two wires between the amp and each speaker as it already will be.

I think that is what is confusing me. I am taking the two + and two - leads from two speaker outputs, and connecting them to the high level input which also has two + inputs but only one -, which the instructions say to connect to the chassis!?

Make sure you phase the speakers correctly

I'm cool with phasing (that's something at least)!

 

[Ted]

OK, so the fact this is a mono amp and I am only wiring up a single sub means that it is still not a problem (correct me if I am wrong!).

Just realised that this is a mono amp! so correct - this isn't a problem.

OK, the high level input for this is coming from the AGW / Audio GateWay (existing car amp). Is it a fair assumption the grounds will be common, or is it better to get my multimeter out?


I think that it is a fair assumption, however, personally I would also check. 99% sure that it would be perfectly safe to common up both of the returns from the audio gateway.

I think that is what is confusing me. I am taking the two + and two - leads from two speaker outputs, and connecting them to the high level input which also has two + inputs but only one -, which the instructions say to connect to the chassis!?

My take on it is this. The two negatives into one makes sense (as per previous paragraph). Pretty sure that the advice to connect them to ground also makes sense to reduce noise - all of this is common practice on 'low' output systems.
I think the confusion is where it says that the OUTPUT is floating and shouldn't be connected to ground - again, this is correct - remember that the output is totally seperate to the input - other than the amplification, there is nothing common between the two.

Now, I stand to be corrected as it is a long time since I did any of this.

Your amp is probably a class C amp which involves a push/pull final output stage. This is why the output is floating.

'normal' amps (lower output) are (were) usually a class A - (actually (arguably) a better amp as there is no crossover distortion) and these are in my experience referenced to a common ground.

Apologies if I haven't explained that well or if it is inaccurate - as I said, it was all a long time ago

Bottom line - I'm 99% sure that all will be ok, to the point where I would go for it myself.

 

[V12]

Agree with above, that's how i read the manual.

 

[sinewave]

Load of myther all this ICE lark!

 

[John]

Thanks Ted, much appreciated.

The amp is a Class D as it happens but I imagine it is a similar scenario.

Your explanation is fine - it's the industry-specific lingo that I struggle with but I can look it up.

I've done numerous installs but all grounds have been ground to chassis.

This is the first time in nearly 20 years I've been stuck!

 

[Diesel Benz]

Just bought a new amp to go in my car. Not had to use high level inputs before and reading through the amp instructions, it uses a 'floating ground' so I am not totally sure what I am going to ground the negative speakers wires to (high level input) as it suggests grounding it to the car receiver.

Given where that is , is there another (more convenient) ground which can be used (I'm thinking AWG or something)?

I'm quite confused about the instructions here, I hope you were able to follow those. I'll try to put this with other words, hopefully not creating more confusion than clarity.

The output side seems to be clear already, the amp has two separate connectors for the single speaker to be installed. One should not get confused from the speaker+/- wire notation, the minus wire is nothing like ground (the plus is obvious that it isn't battery +). As mentioned, it is a bridged (class D) amp where the minus output can go from (almost) -12 V to + 12 V, exactly the same with the plus output (they just do it with a 180 degree phase difference).

The AGW outputs are the same type as this new amp would have, the minus output is not grounded and none of the minus wires for different speakers are common. Luckily this amp has an integrated high level input converter, meaning it accepts direct speaker level inputs from another (bridged) amp. Meaning one should connect one of the speaker wire pairs from the AGW (if it already has a specific output for a sub-woofer, then that).

Take the speaker minus wire to the high level input minus, the speaker plus wire to the high level input plus and ground the high level input ground wire to the chassis ground, preferably somewhere close to the point the AGW ground wire is connected.

 

[Ted]

just to clear a couple of things up.

Ground is just a term for a common point from which voltages are referenced. It is convenient, but not necessary to use this point.
If you generate a voltage, but don't reference (or connect one end!) to ground, you can consider it to be floating.
Ground in a piece of equipment and ground on a car may not be at the same potential, so you could have two grounds. Connecting them together would create a common ground point.

From Ohm's law, if you have a nominal 12V supply into 4ohm speakers, the maximum wattage you can obtain is 36 (per channel). This assumes zero loss. The only way to increase this is lower impedence speakers and/or an inverter in the amp to boost the internal voltages. As Diesel-Benz says, this will allow a dual rail supply.

And last of all, as I said, earlier, all voltages are eith respect to a certain point. If you choose to use the positive terminal of your battery as your reference point, then all voltages on your car are NEGATIVE. (not that anyone would do this as it would confuse the hell out of everyone). This is not the same as 'positive earth'.

 

[John]

Cheers all

...I never knew electronics could be such fun.

I did look into some of the terms but also found other posts from people asking what to do with the + and - wires, where only the + leads are used the '-' ones are simply not used (which correlates with the manual). Not sure I will get that but it's not relevant I do either - all I care is I connect it correctly!

So up until I read this thread today - this is what I understood:

The JVC amp is mono and has a single + and - output which I will connect to the subwoofer. That's fine. The power for it is all fine.

I've already cut into the rear speaker channels with bullets and they are currently connected together (I'm still making the mount for the sub).

I will be disconnecting these and connecting a self-made lead with speaker cable which allows them to be reconnected (so the rear speakers work) and then leads with a smaller grade of cable connected in parallel at the source end will allow the speaker output to connected to the high level input of the JVC amp.

The JVC amp high level input has a pre-constructed lead already which has 3 wires and a small plug. Wires 1 and 3, if you like, are taken from the RL channel + wire and RR channel + wires. So my self-made lead will connect both + wires to the + wires of the pre-constructed lead via soldered joins.

This is what I couldn't get my head around at first (as I've historically had to do something with the '-' wires) but I believe the respective '-' wires, per RL and RR above, are simply taped up separately. The 'CAUTIONS AND NOTES' section states:

Do not connect the - terminals of the speakers to each other.
Do not connect the - terminals of the speakers to the body or chassis.

So I was simply going to not bother tapping into them at all and just tap into the RL and RR positive leads only meaning I wouldn't have to do anything with them...

Then, the middle '-' wire of the supplied high level input plug I was going to connect to a close ground point (it advises about connecting it to a JVC receiver or a.n.other device ground etc.) to avoid noise.

This does contradict with some of the information on this thread but this exercise has helped me to understand at least where the wires go - even if the reasons why make no sense to me!

Thoughts?

 

[Diesel Benz]

The JVC amp high level input has a pre-constructed lead already which has 3 wires and a small plug. Wires 1 and 3, if you like, are taken from the RL channel + wire and RR channel + wires. So my self-made lead will connect both + wires to the + wires of the pre-constructed lead via soldered joins.

This is what I couldn't get my head around at first (as I've historically had to do something with the '-' wires) but I believe the respective '-' wires, per RL and RR above, are simply taped up separately. The 'CAUTIONS AND NOTES' section states:

Do not connect the - terminals of the speakers to each other.
Do not connect the - terminals of the speakers to the body or chassis.

So I was simply going to not bother tapping into them at all and just tap into the RL and RR positive leads only meaning I wouldn't have to do anything with them...

Then, the middle '-' wire of the supplied high level input plug I was going to connect to a close ground point (it advises about connecting it to a JVC receiver or a.n.other device ground etc.) to avoid noise.

I don't think I could follow your exact plan for the wiring. I understand you have a single channel sub-woofer amplifier where you need a single channel signal input. Now if your plan is not to use the RL/RR negative speaker wires at all, did you then plan to use the RL positive and the RR positive wires and connect those to the amp minus and plus high level inputs?

This would not work, low frequencies are usually fed at the same level on both the left and the right stereo channels (because one is not able to detect the direction of a low frequency signal, no stereo image anyway) and the amplifier would not see any input signal. It is the difference between the high level input plus and minus inputs that the amplifier would see as the actual audio signal and would amplify that.

The warnings from the manual are related to the previous discussion in this thread about no common ground (or any other signal) between any of the 4 channels. No danger to pick up e.g. the RL minus wire and feed it to the amplifier minus wire, then the RL speaker plus wire to the amp plus input. The third signal, the ground you can do as you planned.

I was assuming that you are installing a sub-woofer but now I cannot find any reference to that. Is your plan to add an amplifier and to reuse existing speakers? You would need at least two of those single channel amps then. And even there I'm afraid your current speakers would not handle the power from the new amp. If your plan was to install a new sub-woofer speaker and to feed that speaker with the new single channel amp, then you have almost completed the task.

 

[John]

So the ultimate plan is - currently have 4 woofers and 4 tweeters and a 'centre speaker'. I am adding a mono amplifier running single 10" sub (I don't think there is a reference which may add to the confusion - except an off-the-wall remark about the fact I was still working on the sub in post 14!).

I am using the existing channels which run from the AGW to the rear woofers and tweeters (one channel splits into two for woofer and tweeter). However, I am not disabling them - the signal from the AGW will still get to those speakers but will also be tapped off to supply signal to the new mono amp - which requires a stereo input.

This probably shows it better than I could:

Support | JVC United Kingdom

...at the bottom of page 2 on the right lists the wiring inputs for KS-AX3101D and 'subwoofer system' (Section B rather than A).

To get the signal to the new mono amp:

AGW RL+ > High Level Input Left & Original Speaker (2 wires crimped together at the AGW end - but split out to original speakers and new mono amp)
AGW RL- > Original Speaker only (connected directly)
AGW RR+ > High Level Input Right & Original Speaker (2 wires crimped together at the AGW end - but split out to original speakers and new mono amp)
AGW RR- > Original Speaker only (connected directly

 

[Diesel Benz]

Thanks for being persistent. The high level input on this device isn't what I thought (perhaps even typical, I've not used amps with integrated high level inputs).

From the drawing it indeed wants to have the positive speaker signal (I'm sure the negative signal from each would equally work) from the left and the rear channels and a ground reference. Looks like the amplifier internally sums up the left and the right channels (in case the music source is not balanced for low frequencies).

A bit strange that the amp would not use both wires from both speaker channels. After all, the actual signal from each channel may well differ if measured between chassis ground and speaker wire compared to that between the speaker plus and minus (I mean not only different by amplitude/gain). In case you observe some noise when the signals are detected against the chassis ground, you could throw a line level converter and feed the amp line inputs with that.

You should be ready to go, and sorry about the confusion when I did not read the amp diagrams carefully.

A pity the old posts are closed, cannot add a warning about the mistake.

 

[C30077]

Yep, sometimes wiring goes really well and sometimes not. You also have to watch metal cuts when pulling wires.

 

[John]

Thanks for being persistent.

Likewise... and to everyone else on this one. Much appreciated.

Like I put above - high level inputs is new to me as well. I normally upgraded the whole system (from the days when car audio really was sh*t) which started from a high spec head unit running 4v RCA to 2 x amps which split out into subwoofer and woofers / tweeters etc.

However, because I have NoHK NoLogic 6 (instead of HK Logic 7), I am modifying to make it NoHK NoLogic 7! The woofers and tweeters already installed are excellent so no point in touching them.

I will bear the noise issue in mind - cheers. I am hoping the gadgetry in the amp will not need but a separate converter is an option.

A pity the old posts are closed, cannot add a warning about the mistake.

True, but then again, I posted a link to the manual and one should normally take the manual as gospel anyway...

I still don't get it but at least I know exactly what I am doing.

I've mounted the sub, the amp and am now wiring it in.

Cheers C30077 - I am taking my time on this install and so far it is working out well. I don't need to run wires front to back - all my wiring is done in the boot (carefully!).