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#1 2010-03-01 17:45:54

InactiveX
The Last Ninja
From: England
Registered: 2008-08-14
Posts: 280

Ground Loop Isolators - Some Strange Results

Following the advice of Ready, I decided to add ground loop isolators to the outputs of my SIDs to protect them (thanks Ready!):

http://www.mssiah-forum.com/viewtopic.php?id=1081

These are the isolators I used:

http://www.amazon.co.uk/Link-quality-gr … B000NVWB9O

I'm getting some very strange results. I did the mod on my first C-64 (dual 6581 SID) and it worked very nicely.

I then did the exact same mod on my second Commie, a dual 6582 C-64...

The sound only came out of SID 1. I checked everything and no change. I swapped around isolators, taking the one that had worked successfully in the 6581 computer. Still the same, only SID 1 was singing.

I tried the isolator that hadn't worked with my dual 6582s and plugged that into the dual 6581s, and it worked great!

So, I have two C-64s, two isolators. One C-64 (6581) works fine on both SIDs with an isolator installed, the other C-64 (6582) will only output on one SID with either isolator used. As soon as the isolator is removed from the dual 6582 C-64, it works again on both SIDS.

Does anyone have any idea how I could use the isolator on my dual 6581 C-64? Thanks!

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#2 2010-03-23 16:57:55

Musssid
Rockford
Registered: 2010-02-11
Posts: 54

Re: Ground Loop Isolators - Some Strange Results

Sorry I don't have a explaination for this only that I purchased the same isolator from amazon and it didn't really do much except make the sid quieter. It is on a sis2sid board but with only one sid at the moment as I blew another one.

Just to add it is a rev b breadbin with 6581 sid

Last edited by Musssid (2010-03-23 17:00:31)

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#3 2010-03-26 12:25:47

Ready.
Bomb Jack
Registered: 2007-01-04
Posts: 30

Re: Ground Loop Isolators - Some Strange Results

@ InactiveX: strange. I don't have a stereo SID, so I cannot really test this. But I can suggest you some trouble shooting:

Plug the ground loop only on 6582 SID2 output and see if anything happens. Nothing plugged to SID1.

Furthermore, what kind of stereo SID board are you using? Does the 6581 commie have the same kind of board as the 6582 commie?

One more question: how is the dual audio output made? do you have 2 RCAs? If so, you should have the signal on center pin and ground on the outer rig contact of each RCA. The grounds of both audio outputs should be common, but please check the ground is present also on the SID2 RCA output. You can check this with an ohmmeter: just measure the resistance between the two RCAs ring contacts (with equipment off)

Another test: does the 6582 SID2 give any audio signal without the ground loop if the 6582 SID1 out is disconneted? Plug just the SID2 out into the amplifier, not SID1 out

What I suspect is that the ground is carried only by SID1 output.

@ Mussid: what do you mean: "...and it didn't really do much..."? if you hear the SID quiter, it means it works and gives the output. Regarding the lower volume of the signal, well it might eat some power, but not that much according to my exerience.

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#4 2010-03-27 17:49:09

Musssid
Rockford
Registered: 2010-02-11
Posts: 54

Re: Ground Loop Isolators - Some Strange Results

Basically all it did was make the sid very quiet, so I turned the sound up and I can still here the noise and interferance.

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#5 2010-03-28 03:05:42

InactiveX
The Last Ninja
From: England
Registered: 2008-08-14
Posts: 280

Re: Ground Loop Isolators - Some Strange Results

Thanks Ready. I'll open her up over the next few days and report back what I find.

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#6 2010-03-29 15:21:51

InactiveX
The Last Ninja
From: England
Registered: 2008-08-14
Posts: 280

Re: Ground Loop Isolators - Some Strange Results

I've tried your suggestions Ready, but no joy.

I've also tested the connections, particularly grounds, with my multimeter. All is hooked up right. I tried your idea of using the multimeter to measure the RCA's rings are connected - they are.

I am using SID2SID boards on both Commies.

Any other ideas? I'm stumped! Thanks.

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#7 2010-04-26 10:40:14

Ready.
Bomb Jack
Registered: 2007-01-04
Posts: 30

Re: Ground Loop Isolators - Some Strange Results

I really don't have any other idea about this issue.... I am stumped as well sad

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#8 2010-11-26 08:52:28

Ready.
Bomb Jack
Registered: 2007-01-04
Posts: 30

Re: Ground Loop Isolators - Some Strange Results

it would be nice if other users could post their results using audio ground loops isolators.

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#9 2011-04-15 16:55:10

InactiveX
The Last Ninja
From: England
Registered: 2008-08-14
Posts: 280

Re: Ground Loop Isolators - Some Strange Results

To revisit this: I've just got hold of a new mainboard (made in 1990) which has a much sharper display than my old C64 when using the RF connector, and have this board in the old case alongside a ground loop isolator.

I've decided to do without SID2SID this time round (I don't really use two SIDs), so have used one side of a stereo isolator. It's sounding great, full of beef.

I fixed it inside the breadbin case, directly wired to the audio out trace and with the other end soldered to a 1/4" socket. With any luck, I'll be able to plug it into anything and won't do the SID a nasty.

Last edited by InactiveX (2011-04-15 17:08:40)

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#10 2011-04-26 11:07:16

Ready.
Bomb Jack
Registered: 2007-01-04
Posts: 30

Re: Ground Loop Isolators - Some Strange Results

Great to read that, InactiveX. I have been using ground loops at SID outputs of my Commodores and never blew a single SID, still sounding great. I haven't tried the stereo mod, thou.

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#11 2011-04-26 16:09:25

InactiveX
The Last Ninja
From: England
Registered: 2008-08-14
Posts: 280

Re: Ground Loop Isolators - Some Strange Results

Sounds like good advice then! Cheers Ready.

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