Hi,

Firstly (Tony), apologies if this has been covered before as I can't seem to find this one in the FAQ or by searching.

I have just spent a very long time chasing out the dreaded alternator whine, and traced it to the fact that by design, only the rear RCAs are grounded inside the Empeg.

Why are only the rear sled outputs grounded and not the fronts and AUX? Is this a design feature to prevent formation of ground loops, or an oversight? as when using a multiple amplifier system, the front signal ground is left floating and is open to induced noise in the RCA lead.

This was cured by the addition of ground leads from my RCA plugs to my new SUPERgound(tm) wire installed in a previous attempt to rid my system of the aforementioned whine.

Oli.

Did I hear 'alternator whine'?

I am the King of alternator whine as my many posts in the past can attest to......

Please provide some details on what you did to rid yourself of this harrowing experience so maybe i can put my system to rest!

Thanks,

Ed

Firstly (Tony), apologies if this has been covered before as I can't seem to find this one in the FAQ or by searching.

It's not in the FAQ because I didn't know about it. This is news to me.

How certain are you that this is by design and not just a flaw on your unit? Can you give a description or photos of exactly what the problem is with your unit? Something to check... are you sure that the RCAs that you say are floating are really the rear output RCAs and not the aux-in RCA's?

It's definitely a FAQ-able item if it turns out to be true.

Given that he claimed the fronts were floating, confirming the rears were seems a bit silly.

Sorry, I got them backwards. But you know what I meant.

..ok...indulge me..what is a 'floating ground'?

Hi Tony,

Cue the mists of time....

It all started when I transferred my set up from my trusty old 1986 MK2 Golf 1.3 to my new 1990 MK2 Golf GTI. My set up consists of an Empeg MK2a, one amp running two subs, and another running components in the front. I have stinger triple screened RCAs and 8 gauge ground cable from both amps to a very secure ground.

The trouble started when I picked up a nasty alternator whine which I attributed to a normal ground loop. I double checked all my grounds, cleaned all battery and earth strap points, ran a new ground solely for the Empeg's harness and also running to the sled itself, I was satistied that it wasn't a 'normal' ground loop problem.

I then went after signal. I knew the whine entered the system as a result of docking the empeg, as with the amps powered up, and the Empeg undocked, the noise disappeared. I first tried earthing the RCAs at the amp end knowing that the amps provided a balanced input. No improvement. I then tested the harness to check continuity of the grounds. I discovered that only the rear RCA ground leads were going to ground. So I checked the harness for loose pins, and narrowed it down to something inside the player, I dismantled the player to check the internal connections, and when these tested ok, I removed the main board and started tracing tracks. To my surprise, the front and AUX grounds have nothing connected to them while the rear output has a thick ground connection.

The problem arose because when transferring the system, I decided to run the subs from the rear RCAs and the components from the front RCAs thus separating the grounds that were previously tied together in the old set up.

So I modified the RCA plugs at the head unit end to incorporate two flying ground leads to which I soldered eyelets to and then bolted them to the new ground connection on the back of the sled.

The silence is golden.
Problem solved.

Oli.

If I recall correctly, the PCB is multilayered. If you found the problem by visually tracing tracks, it's possible that you're missing one of the inner layers.

However, if you actually continuity tested the traces themselves, the odds are better that your diagnosis could be accurate.

You mentioned something about your amp having a floating ground? In that case, grounding the RCA shrouds might merely have been solving that issue as opposed to solving a problem in the player?

Maybe someone else with a multimeter can confirm this.

Pins numbered 16, 19 & 22 of the docking connector should connect to the chassis. Only pin 16 is on mine.

The numbers are printed on the inside of the connector at either end.

they are numbered line this looking from at the back of the empeg:
1 2 3 4 5 6 7 8 9 10 11 12
13 14 15 16 17 18 19 20

Well thankyou Oli. I now have whine free audio thanks to you. I always thought it sounded odd and then I realised the whine was only coming from the rears. I popped a ground lifter in circuit and hey presto crystal clear silence.

The mistake I'd made last time was that I was lifting both pairs. It was only your post that made me think about it again.

I'll verify this on both of my Ml2's (an early, early model, and a later one) see what I get..

I'll take care of it tonight and post tomorrow..

Me.

This find could make a lot of folks happy. Good catch if it turns out to be a universal problem!

ummm..what do u mean by 'ground lifter'????

ground isolator

ahhh..is that the little black box with male/female connectors and the little ground wires leading out?

is that the little black box with male/female connectors and the little ground wires leading out?

Depends on the system and on what you're talking about.

A ground loop isolator is a third party device (a black box with RCA leads) that goes inline between the amp and the head unit to remove a ground loop between the two.

A ground lift is a feature built into some amplifiers which deliberately disconnects the RCA ground shields from the amplifier's chassis ground.

edit: To clarify. A ground loop isolator is not the same thing as a ground lift. It's feasible that either one of these things could be built into a black box with RCA leads, but they have two completely different functions. The former separates all electrical connections on the RCA leads between the head and amp while still providing a method for the audio signal to be sent down the wire. A ground lift simply disconnects the shields while leaving the center pin untouched.

is that the little black box with male/female connectors and the little ground wires leading out?

Yes, thats the one. The lifting is simply describing what is actually being done.

The most common way this happens on mk2s is that there's a fault with the main power ground, and the player tries to power itself via the audio grounds - which burn out. We thickened up the traces a bit on the mk2a, but I can believe it could still happen.

Hugo

In reply to:

---

So I modified the RCA plugs at the head unit end to incorporate two flying ground leads to which I soldered eyelets to and then bolted them to the new ground connection on the back of the sled.

---

Could you explain this sentence to me again? I'm suffering from what sounds like exactly the same issue, but I can't figure out what this sentence means. Are you saying you have permanently connected the empeg to the sled? How do you take it out of your car? Perhaps I'm totally failing to understand. I guess I don't know what a flying ground lead is, as opposed to a regular ground lead.

I quickly drew this in ms paint, hopefully you can get a better idea.. I think I understand the concept..

I unscrewed the housing of the plugs on the end of each RCA lead from the amps and then soldered a ground wire to the screen inside the plug. I then attached the ground wire to one of the bolts on the back of the sled bypassing the empeg's harness and going straight to ground.

diagram attached.

Has anyone else managed to verify whether this issue is present on other players?

Oli.

diagram

Andy M:

You described an issue with whine from the REAR, whereas the title of this thread suggests to me that the original poster thought the problem was only with the fronts..

Weird.

Anybody with a Home Dock (from me) can very easily check the FRONT grounds with an ohm meter -- just dock your player, and check resistance between the player's case (use the side vent holes for access) and the rear mounted RCA plugs. Mine measure about 0.0 Ohms: definitely grounded.

Cheers

The fronts in my Mk2a units are definitely all grounded -- anyone with a Home Dock can check this rather easily.

-ml

Hi Mark, thanks for checking your players.

Maybe i have burnt out some tracks somehow. That could be possible with the front ground, but I find it is strange that the AUX ground has also failed as I have never had this connected to anything.

Hugo- do you have a copy of the mk2a PCB design that would make it possible to see if a burnt out front ground would also take out the aux ground?

Also, my front amp is a Rockford with floating ground inputs, so it wouldn't seem unlikely that the empeg could ground through it.

Mark,

I have to say the plugs have been switched round so many times I may have got them mixed up. It was definately the rear speakers, although I hardly ever use the fader/balance control, so it could have been the front pre outs feeding the rear channels on the amp. It's all still repeatable, there's whine on one pair and silence on the others. I'm not in the mood to remove the sled and have a look as it's far too cold outside. I'll probably have another look when it gets a bit warmer.

I'd love to FAQ this. Is there a clear visual inspection method or a certain way to continuity test it?

You described an issue with whine from the REAR, whereas the title of this thread suggests to me that the original poster thought the problem was only with the fronts.

This would be consistent with the title of the thread. If the front connectors were ungrounded, then the rear connectors would act as the ground path and thus have whine.

you can test it with a multimeter like this:

In reply to:

---

Maybe someone else with a multimeter can confirm this.

Pins numbered 16, 19 & 22 of the docking connector should connect to the chassis. Only pin 16 is on mine.

The numbers are printed on the inside of the connector at either end.

they are numbered line this looking from at the back of the empeg:
1 2 3 4 5 6 7 8 9 10 11 12
13 14 15 16 17 18 19 20

---

On mine 16 and 19 are grounded, but not 22.

Stu

Ditto, no ground on 22 on my MkII or MkIIa

I'm pretty sure it's 22 is aux gnd. I seem to remember it goes...

13 +12
14 acc
15 rear L
16 rear gnd
17 rear R
18 front L
19 front gnd
20 front R
21 aux L
22 aux gnd
23 aux R
24 mic

anyone got a spare harness to hand?

you can test it with a multimeter like this:

I meant, a way to test the motherboard directly for burned out traces. Testing the pins on the sled connector is a good first indicator and would be a good way to lead into "next, open the player and check inside for...". But we still need a way to confirm burned out traces, as well as a way to fix it if it turns out to be the problem.

oops, misunderstood.

the next thing i did was to open up the player, remove the drive tray, pull the analogue connector out and test continuity from the gnd pins in the header to the chassis.

I actually removed the main board from the chassis to do this and I was able to see very thin traces which appeared to be for signal which went from the header through some decoupling capacitors to the pre-amp stage. There was also one relatively thick trace that appeared to go to the rear gnd pin, but without de-soldering the header I was unable to see where it went and if it also connected to the front gnd. Obviously I could only see the top and bottom layers but i would imagine that there wouldn't be too much in other layers as to keep RF interference to a minimum in the output stage.

maybe Hugo could post a small section of the PCB design to see what happens on all the layers around the analogue connector?

Aux isn't grounded, it's a floating ground to cancel common mode noise on the aux inputs. I'm afraid I'm not in the UK at the moment, so posting an image of that part of the PCB isn't easy - Patrick could though, if he's reading?

Hugo

(This seems like a good place to stick a little note restating something that I've seen mentioned before. As Hugo says the aux input should be grounded if the device connected to it isn't grounded to the car body somewhere else, like a portable CD player. If the device is battery powered that make sense, but what's a good way to proced if the aux input device is getting power from the cigarette lighter? I suppose it depends on the internal construction of the player.)

--Nathan

Does anyone know if there are two separate ground traces for the front and rear from the connector on the PCB? it is possible for one to burn out and the other to remain intact?

Oli.