Common to Floating Ground for Speakers

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weeegoneeer
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Joined: Wed Apr 26, 2017 10:34 am

Common to Floating Ground for Speakers

Post by weeegoneeer »

Hey all!

Currently have my dash apart and AC dropped & am making a new harness to clean up the bowl of spaghetti back there, along with a few repairs and in general making sure everything is tight & straight. One thing I want to tackle while back there is to convert the common ground speaker setup to a floating ground to take advantage of my newish radio head.

I do have the Scosche FGA adapter in right now, but really doesn't sound good when turned up - causes really sharp distortion on peaks after a certain volume, almost sounds like additional percussion in the music!

Anyway, has anyone else done this? Where / how did you run the extra wires? Interested in any wisdom folks may have that might save me a couple minutes.

Thanks in advance!
:fsj:
1984 GW
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tgreese
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Re: Common to Floating Ground for Speakers

Post by tgreese »

Isolating the ground just means insulating the speakers and amp from the body and running a dedicated ground wire to each. If you want to keep noise out of the stereo, I suggest a Corcom type filter like used on the mains in noise-sensitive equipment. Run your dedicated power and ground through the filter, and ground the filter case to the body. These filters are easy to find new or surplus. I have used the Corcom filters to shield scientific equipment from environmental RF and they are very effective.

Example: https://www.amazon.com/Corcom-10VR1-EMI ... B005T90GME

Can be found cheaply at hamfests too.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
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tgreese
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Re: Common to Floating Ground for Speakers

Post by tgreese »

Also, if your amp sounds bad when it's turned up it's being overdriven to distortion either because the amp is clipping or the power supply is pooping out (ie caps too small). Could also be that the first stage is being overdriven by the signal source and the output stage is passing on the clipped signal. You could try adding some attenuation between the source and amp.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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tgreese
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Re: Common to Floating Ground for Speakers

Post by tgreese »

Ok, reading a little about this, FGAs are bad in terms of sound - strictly low-fi. The radio has balanced outputs, and using a common ground will kill the radio - thus the FGA. Instead, run a dedicated ground to each speaker (two wires for each channel).
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

Topic author
weeegoneeer
Posts: 230
Joined: Wed Apr 26, 2017 10:34 am

Re: Common to Floating Ground for Speakers

Post by weeegoneeer »

Thanks Tim!

Yeah - it's 100% the FGA that's making it sound horrible - had the same head on a proper circuit in the '87 and could go all the way up.

As far as this:
Ok, reading a little about this, FGAs are bad in terms of sound - strictly low-fi. The radio has balanced outputs, and using a common ground will kill the radio - thus the FGA. Instead, run a dedicated ground to each speaker (two wires for each channel).


Any tips on where to run the extra wires for the rear? The front is easy enough, but for the rear wanted to check if anyone has experience running it under the carpet, or following the frame harness outside of the cabin (why'd they do that?!?!?!), or maybe above the headliner?

Know it's a small/stupid question but 100% down for saving an hour or two if anyone's done it & has pointers.

Thanks guys!
1984 GW
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HeavyMetalThunder_81
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Re: Common to Floating Ground for Speakers

Post by HeavyMetalThunder_81 »

Run them under the carpet with the other factory wires under there.
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Topic author
weeegoneeer
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Joined: Wed Apr 26, 2017 10:34 am

Re: Common to Floating Ground for Speakers

Post by weeegoneeer »

Thanks!
1984 GW
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