Ground Loop

I get a background buzzing which varies according to the Empeg's activity e.g. disk accesses, button presses etc.
It has been present since I originally installed the amp/Empeg and now we have better weather over here I've spent some time recently trying to cure it.

For the record, I also get slight alternator whine with the engine running but I'm not bothered about that here (unless I need to be!).

I've managed to make a cumulative but worthwhile improvement (see below) but the noise is still there and it's starting to bug me!

In the hope that somebody reading this might be able to offer some tips I've listed below things I can be fairly certain of:

FACTS
• Present with engine off
• Level is constant i.e. does not vary with Empeg's volume setting
• Same either in Pause, zero volume or AUX input (no aux device attached) mode
• Disappears when the 4 RCAs are disconnected (from either end)
• Worsens slightly when RCAs are slid back a little so they don't ground
• No difference with Empeg & sled on seat (in case of inadvertant grounding while in dash)

ACTIONS
• Relocated input leads away from power & ground leads
• Checked for other ground paths in the speaker wiring - none present.
• Rewired the grounding (seat mounting point: paint stripped & cleaned) for Empeg & amp using a *star* configuration (slight improvement)
• 3 ground leads of equal length/guage to: Amplifier, Empeg harness & docking sled (Grounding the sled gave a slight improvement)

OBSERVATIONS
• Grounding an RCA tip to the Empeg casing will produce this noise.
• Squeezing top & bottom at the sled pips - improves vastly (depending upon pressure)
• Grounding an RCA tip on the Empeg harness ground - no noise.
• While using the detached sled ground as a flying lead:-
>Grounding pin-5 (gnd) on the RS232 plug - disappears
>Grounding the Empeg chassis (much less so against the top cover) while in the sled - disappears
>Grounding the AC RCA outters - disappears
>Grounding an earth braid at the docking connector - slight improvement


Crutchfield's troubleshooting guide (indirectly linked from the excellent Empeg FAQ) suggested a power filter - I don't own one/haven't tried one and need to be convinced further.

Referring back to my Observations the solution would appear quite simple; All I need is a good ground to the Empeg chassis/signal ground.
While I don't trust my Digital VoltMeter with readings less than 1ohm I firmly believe there is a very good contact (and I've cleaned them both) between the sled and the body of the Empeg. I know that squeezing the two together improves the connection but I know that persuing this further (E.g. ad-hoc earth contact springs added to the sled etc.) must surely be sidestepping the root cause.

Suggestions (please)?

Edit: Typo's & grammatical errors

>Grounding pin-5 (gnd) on the RS232 plug - disappears
>Grounding the Empeg chassis (much less so against the top cover) while in the sled - disappears
>Grounding the AC RCA outters - disappears

It seems you've gone to a lot of trouble to diagnose it. From what you've said in the above-quoted lines that you've already found the solution. Ground the player chassis or the RCA shrouds and you're done? Or am I missing someting?

One thing you didn't say: Whether you own a Mk1 or a Mk2 player. If you own a Mk1 player, this is actually expected, there were even a set of RCA ground adapters just for this purpose included with the Mk1 player.

Ground the player chassis or the RCA shrouds and you're done? Or am I missing someting?

I just feel that by persuing an ad-hoc fix such as a 'special' ground (spring?) I am possibly sidestepping the real cause of the problem. Given the number of Empeg's installed to-date, I can't help but think that _I_ must surely have something wrong in my install otherwise:
a. It would have cropped up before (E.g. appeared in the FAQ)
b. The need for a special earth in the sled would be a design flaw (I don't buy that especially given the no.of previous installs).

One thing you didn't say: Whether you own a Mk1 or a Mk2 player
It's a MK2

Edit. Reworded item b.

Well, if it really solves the problem, I'd just ground the RCA shrouds and be done with it.

Pleny of people have ended up ground the sled seperatly. I think it's the boxter contingent that is extra prone to having to do it to get rid of noise. If it works, just run the ground line and forget about it.

Matthew

How is everyone fastening the ground wire to the sled?

I'd use the screw hole provided if I had to do it.

Maybe the ground pin on the docking connector of the sled is not properly seated or making a good contact with the empeg.
I had this problem at one point.

Check out this pin and the crimp to the ground wire.

How is everyone fastening the ground wire to the sled?

Same as Tony: I'm using the threaded hole at the rear.

My ground lead has a crimped-on 'eye' and I use a star washer between it and the sled.

Maybe the ground pin on the docking connector of the sled is not properly seated or making a good contact with the empeg.

Good point, I'll give it a thorough check. I did give it a quick visual check yesterday but assumed that since the Empeg was powering up it must be ok.

I'm ignorant... what's the best way to check?

Maybe the ground pin on the docking connector of the sled is not properly seated

Good point. Check to make sure that the ground wire coming out of the back of the sled docking connector isn't loose, i.e., pulling out of the crimp as described here.

Also check to make sure that wire is properly attached to the vehicle. For instance, make sure it's grounded to a proper place.

The grounding point is centrally located on the rear face of the sled. This photo (of Christian's De-Lorean install) shows it being used to attach to the vertical support bracket.

I tried using that screw hole, but for the life of me, I couldn't find a properly sized screw to fit... So I attached it with one of the screws holding the docking connector. Not the most elligant solution, but it got rid of 80% or so of my whine. Considering what hell my drive upgrade has been (see Technical), it was good to have one thing go right..

Now.. tracking down that last 20%...

I tried using that screw hole, but for the life of me, I couldn't find a properly sized screw to fit...

You've got a point, there. Just last night I needed to get a screw for that thread, and I had a heck of a time finding one.

I did find one eventually, but it was tough.

Note, if anyone knows the size and thread of it, do share!

Note, if anyone knows the size and thread of it, do share!

I used this screw on my install and I'm pretty sure it's a standard metric thread of M4 or M5 size. I had a suitable screw in my toolbox anyway.

Standard M4 thread (not fine or anything like that, just plain M4)

/Michael

Thank you guys!

(ps - how do you ground RCA's?)

how do you ground RCA's?)

They're supposed to be connected to the ground of the equipment at each end through the outer shield (or one of the wires if you have twisted pair RCAs), unless you have RCAs with only one end of the shield connected to the connector (can solve some ground loop problems).

To add extra grounding to an existing RCA cable, I'd probably solder on a wire to the outside of the connector (the springy part) - quick and easy. But exactly how would depend on the type of RCA connector. For instance, on the ones on a MkI I'd try to screw it apart and solder to the terminal directly (looks neater), but if the RCA plug is molded around the cable I'd just solder to the outside...

/Michael

I will probably mount an earthed spring in the back of the sled which will earth the AC RCAs to cure my ground loop. I say probably because I've not decided whether or not to try an isolator on the RCAs instead. Currently stuck between the idea of modifying the sled [guaranteed cure] or buying an isolator [result presently unknown].

On the subject of Ground Isolators: What exactly are they, small transformers?
I will be going to a scrap yard in a few days, might I possibly find them factory-fitted to certain cars, if so what make (& model)?

On the subject of Ground Isolators: What exactly are they, small transformers?

Proper ones are optical isolators. They convert the audio signal from DC hardwired voltage to optical and back again, effectively severing the path for the ground loop.

This works in pretty much every case. However, it is yet another stage of conversions for the audio signal chain, and as such, there is some audio quality sacrificed in the process.

For instance, the one you can get at Radio Shack specs a frequency range which effectively removes the lowest frequencies from the audio signal. For some people, this would be an unacceptable trade-off. There have been other isolators mentioned on this BBS that are supposedly higher quality than the RatShack ones. If anyone can provide me with an online link to where you can buy the higher-quality ones, I will add that information to the FAQ.

Something to keep in mind: Opto-isolators cost money and are, in most cases, not needed if you could simply locate and fix the ground resistance. Using an isolator is a quick and dirty fix, putting a band-aid on the problem without solving its root cause. Why pay money for something you didn't actually need?

Proper ones are optical isolators

That may be true, but every ground loop isolator I've seen has been a simple 1:1 transformer.

Rob

Really, I thought they said the "good" one mentioned elsewhere on this BBS was an opto-isolator. I could be remembering it wrong.

Unless it was mentioned in the context of me having seen one, then I don't think I have.. that's not to say they wouldn't be better, I'm just making the point that they're not very common.

Rob

For instance, the one you can get at Radio Shack specs a frequency range which effectively removes the lowest frequencies from the audio signal.

Dang. Used those before. Off I go to Ratshacks site to check it out. Hmmm... Something odd here...
Under "Specifications" it lists some alarming numbers for the frequency response. That can't be right, everything would sound like it's being played through mud. But under "Diagram", the freq response curve is laudably flat:

>http://support.radioshack.com/support_auto/9643.htm

Any idea what's what?

Wouldn't that frequency response mean that that is just the range of frequencies the isolator focuses on? For instance, if you somehow had ground loop noise outside of that range, it wouldn't be cancelled out, but ground loop noise within the specified range would be. At least that's my guess.

I don't think that GLI's are meant to isolate frequencies. They are meant to provide a way of blocking a components access to ground through the RCA cable.