grounding confusion!

cburn · Joined: Feb 22, 2015 Posts: 8 Location: Earth

Hi,

Is it bad to use several grounding points for a device? Especially when it comes to input and outputs? I just can not get this device to work as I want.

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I am really just trying to get the ins and outs of a Sparkomatic car audio EQ to rca female or some other audio connector (the speakers included).

It has 4 channels out (speakers) with a ground connection each and 2 channels out with a shared ground.

When I disconnect the ground at for example the input channels something good happens at some place (like hum goes away), something else is gone (like panning).

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PHOBoS · Posted: Sun Feb 22, 2015 5:46 am Post subject:

I can't say a whole lot about it but car amplifiers are usually the bridged type, which means that there are
2 amplifiers for each speaker with one being inverted. So the - is not the same as GND!

If you want to use this signal it should work if you only take the + speaker out and use the common GND,
or you could use a suitable transformer. You'll probably have to bring the signal level down though if you
want to convert it to RCA. With a transformer that can be done in one go otherwise 2 resistors as a voltage
divider could do it.

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cburn · Joined: Feb 22, 2015 Posts: 8 Location: Earth

Ahh, ok thanks. I need to do some wiki reading on ground, earth, common etc.

But in the meanwhile, common GND would be the one from line in, right?

Also, say that I just want to attach a bunch of headphones (which would be equivalent to speakers), would your suggested solution still apply?

Thanks a lot!

PHOBoS · Posted: Sun Feb 22, 2015 10:53 am Post subject:

yes the common GND is the shared GND which should be the one on your line in and the - of your power.
At least for car stereo where the - is GND. Earth doesn't apply here it's what you have on a mains connection and is literaly
a connection to the earth. Usually this will also be connected to GND but in some cases this can cause problems.

For headphones you wouldn't need anything special since it's just some speakers so you connect them in the same way.
Be careful though the output might be more than your headphones can handle. If you use a connector for your headphones
than you have to make sure it's isolated from the chassis/GND. (because of the bridged amplifier)

edit: just realized that on a headphones both - connection of the speakers are connected together so that
wouldn't actually work. However I think connecting it between + speaker output and GND should.

cburn · Joined: Feb 22, 2015 Posts: 8 Location: Earth

I got it working now, thanks a lot.

I too assumed that the shared - on the headphones would be a problem, but I "solved" that by using a pair of headphones on each channel.

Maybe I will try a more flexible solution later, but this is the setup originally intended so it will do fine.

awesome!

Btw, one pair of the headphones makes a "sucking " sound, as if the speaker violently moves (maybe the wrong way), when I connect it to one of the (rca) jacks. Could this be the symptom of common GND touching the + or -? Of course I will just go over the connections, still it is nice to if possible know the reason.