Garmin 276C voice-out into Autocomm: problem

[Joe Frickin' Friday]

I have a Garmin 276C GPS receiver. On my previous bike I only wired in chassis power to feed the GPS, but on current bike ('09 R1200RT), I also wired the audio/voice output from the GPS unit to feed into the Autocom.

 

The connector that plugs into the GPS looks like this:

 

 

I connected the Voice (-) and Voice (+) to a phono plug:

 

The orange wire (Voice -) went to the shield/ground ring, and the brown (Voice +) wire went to both the L and R rings.

 

The phono plug is plugged into the "Auxiliary 2" phono jack on the end of my Autocom Pro 7 Sport box under the rear saddle (the other jack, "Music Input," is connected to my MP3 player).

 

 

The problem:

When the GPS receiver puts a signal on those speaker wires (as for an upcoming turn), I don't hear a voice in my helmet; instead, I just get a loud buzzing. Been this way since I wired it up last summer, but now that I've got the bike apart for maintenance I decided to troubleshoot it.

 

First suspect was bad wiring on my part. To test, I took the phono plug out of the Autocomm and connected the plug to a pair of headphones, then had the GPS receiver simulate a drive across town. Suddenly my ears were filled with the voice of a polite British woman telling me where to go.

 

OK, so my wiring connections seem to be in order.

 

That means there's a problem with my Autocom box.

 

The MP3 player comes through loud and clear in my helmet's headset, so I tried taking the GPS receiver's phono plug and putting into the other jack on the Autocom ("Music Input," the one the MP3 player had been using). Same buzzing noise when I should be hearing verbal directions.

 

So, to sum up:

 

-GPS receiver's voice output, when wired directly to a pair of headphones, comes through loud and clear.

 

-Autocomm Pro 7 Sport has two accessory inputs, labeled "Music Input" and "Auxiliary 2". Either one will take a signal from my MP3 player and pass it through to my helmet's headset.

 

-NEITHER one will take a signal from my GPS receiver; the Autocomm remains silent when the GPS is silent, but replaces the voice directions with a loud buzzing sound.

 

What gives? Some kinda weird impedance mismatch? How do I fix this???

[EddyQ]

Does the GPS signal sound good through the autocom when isolated from the bike? Run the GPS off its internal batteries and see what happens (no ground connections either). I think you are getting noise through the power wires(but from what source?). What is the data in the GPS cable? How do you connect the grounds?

[markgoodrich]

Ah, man, you got the Bee version of the 276c. What you're hearing is corerct, you just aren't a bee.

 

Glad I could help.

[EddyQ]

I do not yet have an Autocom, but I found this link which confused me greatly. Seems the Aux input may be 4-pole with all sorts of possible wiring configuration. You connector is 3-pole. Since it works with your mp3, I kinda think it is not a problem.

[Limecreek]

A ground loop isolator between the 276c and the Pro M1 fixed it for me.

 

Filter

[Joe Frickin' Friday]

Does the GPS signal sound good through the autocom when isolated from the bike? Run the GPS off its internal batteries and see what happens (no ground connections either). I think you are getting noise through the power wires(but from what source?). What is the data in the GPS cable? How do you connect the grounds?

 

Sorry for the confusing illustration. That was scanned directly out of the GPS receiver's manual, and shows the entire pinout for the plug. I'm only using the following four wires:

 

Brown (Voice +)

Orange (Voice -)

Power (Red)

Ground (Black)

 

 

The GPS and Autocomm both draw power through an Eastern Beaver PC-8 fuse box. The Autocomm is on switched power; it doesn't come on unless the ignition key is on, at which point the PC-8 connects it to the bike battery through a relay.

 

The GPS is powered through an always-hot terminal on the PC-8. There's a fuse, but other than that, it's basically hard-wired to the battery.

 

Both the GPS and Autocom ground wires are connected to a ground strip on the PC-8, which is in turn connected directly to the battery.

 

All of the symptoms I reported last night were observed without the engine/alternator spinning. However, two observations:

 

1. I don't recall whether I did the headphone test with the bike on or off.

 

2. I didn't try connecting my headphones to the GPS phono plug while the GPS phono plug was connected to the Autocom. I know the GPS voice in the helmet headset is corrupted, but this test would tell me whether it's being corrupted inside the Autocom, or inside the GPS unit. I will try this test tonight (I have a phono splitter that makes this possible).

 

The power and audio are on the same connector for the GPS, so I'll have to pull a wire from the PC-8 to see how the GPS behaves when running on its own internal battery. The rear accessory socket on the bike is what controls the switching relay for the PC-8; it stays on for maybe a minute after turning the ignition key off. I don't have another power source for the Autocomm, so this would have to do for an "isolated from the bike" test.

 

Will do more testing tonight and report back. Thanks for tips so far...

[Joe Frickin' Friday]

A ground loop isolator between the 276c and the Pro M1 fixed it for me.

 

Filter

 

So you had this same buzzing problem?

 

Just so we're clear, I'm not talking about a voice that's got some buzziness to it, or a buzz with a voice-modulated volume. Instead, the entire period that the GPS is supposed to be putting out a voice, there's nothing but one long constant-volume, constant-pitch buzz, regardless of what words the GPS is supposed to be spitting out.

 

I'll post a recording of it tonight, but based on my description, is that what you had?

[Ken H.]

Mitch, this is most likely cause by a ground loop because you are powering both off the bike. The Garmin audio out needs to be ground isolated. Try the mentioned idea of not powering the Garmin off the bike for a test. If this fixes it you need to add the Autocom audio isolation cable between the two.

[flars]

You need a ground loop isolator. Any audio product that runs off bike power that is tied to the autocomm runs the risk of blowing the output circuitry of the device. Tom has repeatedly warned us about this.

I had the same sort of problem when my GLI started to fail (how the heck can they fail, for crying out loud???).

[FlyingFinn]

Not that I have any experience on the that combination of devices: 276C + Pro 7 Sport but I believe other are correct about the ground loop isolator when recommend using one.

 

Here's little background why the GLI is so necessary in many case.

 

In MANY audio devices (probably most, including the speaker outputs in 7-pin Autocom headset connector) the "ground" pin of a speaker output, or Voice- in the case of the Garmin connector diagram, IS NOT GROUND.

 

The final audio amplifier in these devices has a differential output where neither output is a ground. The Out+ swings to one direction and Out- swings to opposite direction.

Neither signal is connected to "ground", or 0V potential. (I suspect the 276C is the same way, see they don't even call it GND)

 

 

Now, if such a balanced audio output is connected to a single-ended audio input, you create a short from the Out- to "ground". In many cases that short can damage the audio output amplifier, sometimes it just doesn't work but causes no permanent damage.

This is why we need to use the "Groud loop isolator", not to really cut a ground loop but to make the balanced audio output compatible with a single-ended audio in.

 

Many portable audio devices have a stern warning in the user manual to NOT connect the headphone output to an external amplifier if both are connected to common ground potential. Not because there could be some noise from a ground loop but because one leg of the balanced headphone amplifier would get shorted to ground and would kill the headphone output.

 

--

Mikko

[EddyQ]

Mitch, this is most likely cause by a ground loop because you are powering both off the bike. The Garmin audio out needs to be ground isolated. Try the mentioned idea of not powering the Garmin off the bike for a test. If this fixes it you need to add the Autocom audio isolation cable between the two.

 

From the connections shown, the GPS "ground wire" which likely has all the noisy currents that the +12V lead has, now has another path (wired connection) back to the battery. That other path is the audio wire (Voice (-)) through the autocom back to common ground and to the battery. Since the wires/connectors do have finite resistance, there will be sharing of the GPS current. Since you have current in the audio "ground" and finite resistance (V=I*R) you get a noisy voltage in your audio. This really isn't a ground loop, but a direct wired coupling of the unwanted noisy signal. By running on the GPS batteries, there will be no noisy currents trying to get back to the bike battery, so the problem (if this is it) would be fixed.

 

I have no idea what is in the autocom isolator that eliminates this. Maybe an audio 1:1 transformer. If so, it may lower volume and limit the frequency response a bit, but completely eliminating the noisy current path.

 

What is weird with this story is how the sound is quiet when the GPS is not talking. I would think the GPS noisy currents would be there regardless of audio output. The problem almost sounds like some feedback is occuring, causing something to oscillate. Maybe the GPS audio is a "bridged amplifier" configurarion where voice (-) should not be grounded? Is it possible the volume on the GPS is far too high? Is the VOX doing weird things?

[FlyingFinn]

What is weird with this story is how the sound is quiet when the GPS is not talking.

 

It's not weird at all.

There's no issue with "ground currents" as long as the audio amplifier in Garmin is not enabled.

As soon as "Garmin starts to talk" the output is enabled and the Voice-, which is not ground, is shorted to ground at the Autocom input.

That causes problems, and potentially kills the audio amp in the Garmin. But likely not since the manufacturers know that users keep making this mistake so they use short-circuit tolerant amps.

 

--

Mikko

[Joe Frickin' Friday]

What is weird with this story is how the sound is quiet when the GPS is not talking.

 

It's not weird at all.

There's no issue with "ground currents" as long as the audio amplifier in Garmin is not enabled.

As soon as "Garmin starts to talk" the output is enabled and the Voice-, which is not ground, is shorted to ground at the Autocom input.

That causes problems, and potentially kills the audio amp in the Garmin. But likely not since the manufacturers know that users keep making this mistake so they use short-circuit tolerant amps.

 

Mikko, thanks for the 'splanation. It all makes sense now, why the MP3 player works fine (no connection at all to the bike power), why the GPS is silent when not talking, and why it just puts out a steady buzz when it's trying to talk (that's when it switches its internal amp in/on, and then thing go to hell, regardless of the words that nice British lady is trying to speak).

 

Stopped by Radio Shack over lunch, bought an isolator. Will try it out tonight and report back.

 

 

[EddyQ]

In MANY audio devices (probably most, including the speaker outputs in 7-pin Autocom headset connector) the "ground" pin of a speaker output, or Voice- in the case of the Garmin connector diagram, IS NOT GROUND.

 

Yup, it is called a bridged amplifier. Link

 

In theory, if you use only one half of the bridge amplifier, it should work.

 

To do that, keep the voice (+) connections, disconnect the voice (-) from the audio barrel and leave open circuit. Then, connect the GND to the barrel connection on the audio connector. This will connect only one side of the bridge amplifier. Volume will decrease 6dB, but the other voice (-) will no longer be shorted.

 

Before you do this (if you choose to do this), be sure there is no DC voltage at the voice(+) output relative to ground. Check it with your trusty DVM set to DC. I would check with and without a voice, just in case the amp has a power down feature where the bias gets switched off. Sometimes, bridge amp outputs are not at 0VDC. If above 0.1V, say 1 VDC or more, I would hesitate to connect as I suggest above since you would be upsetting an audio amplifier bias.

 

Also, be careful. You should where a static strap or somehow safely ground yourself when mucking with electronic stuff. Take your time and be very careful not to wrongfully connect things. +12V into a amp output will likely pop it instantly. Sparks are not your friend!

[EddyQ]

It's not weird at all.

There's no issue with "ground currents" as long as the audio amplifier in Garmin is not enabled.

 

My theory is that the "ground currents" are generated by the +12VDC circuits, likely a bunch of digital stuff, which is typically noisy. And, I believe it would be weird that these digital currents would go away when not talking. Hey, it is just a theory and I may be completely wrong. But to rule it out, you simply run the GPS off its own battery source.

 

Would your theory that "a bridge amplifier output is getting shorted" still produce the noise if the GPS was run on internal batteries. Yes? Maybe not depending on how the noise is getting generated. So how does a shorted amplifier generate noise? I have a few guesses. I can't see how a stressed transistor amplifier will generate signals.

 

Let's see what Mitch's tests conclude before we draw conclusions to exactly what the problem is.

[FlyingFinn]

Would your theory that "a bridge amplifier output is getting shorted" still produce the noise if the GPS was run on internal batteries. Yes?

 

Connecting a balanced audio output to single-ended audio input usually works if the audio source (the GPS in this case) is floating.

 

The issue with making the mistake of connecting balanced audio signal to a single-ended input is not with some noisy ground current. You short half of a balanced amplifier, that just simply not going to work.

 

And yes, there is DC present at the Voice+ and Voice- signals.

Lets say the audio amp is running from +9V VDD. At no-signal situation each half of the output will be sitting somewhere close to 1/2 VDD, lets say +4V. With AC signals (like sound) the output pins swing around that +4V operating point, each moving by the same amout but to oposite directions.

 

If the operating point would be 0VDC then the amp would require a dual supply voltage, like +/-9V. That would require a DC/DC voltage converter -> costs lot more money -> they don't do that.

Or, a very large coupling capacitors could be used at the amplifier output to block the DC voltage but since the output is desiged to drive low impedance headphones and the frequency response needs to go all the way down to few hundred Hz the required capacitor would need to be very large value -> takes way too much space and costs too much money -> they don't do that.

 

--

Mikko

[Joe Frickin' Friday]

Ground isolator did the trick.

 

The loud buzz used to serve as a kind of alarm to remind me to look at the GPS, but I think I'm going to like a voice that speaks actual words much better.

 

Thanks to everyone for your help.

[Lone_RT_rider]

The loud buzz used to serve as a kind of alarm to remind me to look at the GPS, but I think I'm going to like a voice that speaks actual words much better.

 

Oh great, now he can blame all those voices in his head on the GPS. Denial aint just a river in Egypt anymore folks.

[EddyQ]

The issue with making the mistake of connecting balanced audio signal to a single-ended input is not with some noisy ground current.

 

Mikko, I agree with your thoughts 100%. But I wouldn't be so certain that is the architecture of the circuit. Pulse width modulated outputs are really simple to do these days using digital circuits and are more efficient and cheaper. A balanced PWM output will have a DC offset too. And, maybe it creates noise if one side is shorted? If linear amps are used, I'm not seeing how a shorted balanced amp creates its own signals unless it is unstable and oscillating.

 

Whatever.

 

If it was a ground loop, conducted ground noises or unhappy balanced amplifier the isolator would work. And it did.

[Joe Frickin' Friday]

Weird thing is that there is absolutely no mention of ground isolation in the Autocom or Garmin manuals. :confused:

[johnlt]

Mitch, although the RS isolators will work, I found them to be too big for the installation I wanted. There are much smaller versions available including the autocom isolators if you get into a pinch for space.

[Joe Frickin' Friday]

Mitch, although the RS isolators will work, I found them to be too big for the installation I wanted. There are much smaller versions available including the autocom isolators if you get into a pinch for space.

 

Thanks for the tip. It is indeed bulky and comes with about a mile of wire on either end, and needs adapters to get from RCA to phono. I will trim the wires back, solder on dedicated phono plugs, and make it fit; I've already got a bunch of tools in my bike's tail-cave, but there's still plenty of room left.

[EddyQ]

Weird thing is that there is absolutely no mention of ground isolation in the Autocom or Garmin manuals. :confused:

 

Agree.

 

Personnally, I think both companies might have a flawed circuit.

 

Autocom sells a isolator, so why isn't it in every unit?

It is possible the Autocom would work without the isolator, but odds are . . . It would be far better design if it contained one.

 

If Garmin has a bridged amp, they really should tell the end user or provide guidance to hooking it to other systems. It also shouldn't buzz or get damaged when hooked up as you did it.

[John Bentall]

[quote=EddyQAutocom sells a isolator, so why isn't it in every unit?

It is possible the Autocom would work without the isolator, but odds are . . . It would be far better design if it contained one.

 

 

Would you like to pay for a ground-loop isolator that you were never going to use (e.g. rider-pillion only use), just because everyone else wants one?

This topic has been discussed several times and Autocom have a new owner.

[EddyQ]

Would you like to pay for a ground-loop isolator that you were never going to use (e.g. rider-pillion only use), just because everyone else wants one?

 

For a $200 box, the extra few dollars for the device would be worth it to me.

Autocom has a good rep as being a quality, touble free unit and that is why many pay the extra $$ for it.

If I had to spend the time that Mitch and others have done, I wouldn't be happy with my purchace.

I bet there are many folks who are not the tinkering type as Mitch and just could not solve the issue and feel

they were out $200 or more.

[guitardad]

DW and I both run 276C GPS's - hers thru an Autocomm Pro-7, mine thru a Starcom1. Mikko has it right - the 276C does indeed use a bridged audio output. When we initially installed the GPS with her system, we had exactly the same problem. Isolating the low side fixed it, but unfortunately we had damaged the audio driver by then. Her GPS sound comes and goes now.

 

When I installed my unit, I used an audio isolation transformer from Radio Shack between GPS and the Starcom. (P/N 273-1374 at the bottom of this page: http://www.radioshack.com/family/index.jsp?categoryId=2032277) No issues at all.

[KDeline]

 

Agree.

 

 

 

Autocom sells a isolator, so why isn't it in every unit?

It is possible the Autocom would work without the isolator, but odds are . . . It would be far better design if it contained one.

 

 

 

 

So you can spend more money with them silly! I had the same problem with the PRO-7 and the 2720 a few years back with their supplied non isolated wire. They recommended I buy their isolator wire and presto, it worked. More $$$$ into the units, I had to buy 2 because the wife has the same setup.

[KDeline]

[quote=Eddy

 

For a $200 box, the extra few dollars for the device would be worth it to me.

Autocom has a good rep as being a quality, touble free unit and that is why many pay the extra $$ for it.

If I had to spend the time that Mitch and others have done, I wouldn't be happy with my purchace.

I bet there are many folks who are not the tinkering type as Mitch and just could not solve the issue and feel

they were out $200 or more.

 

 

That is were I am at, don't know enough to tinker so am forced to buy the high dollar stuff, thus the rant in the previous post.

[Haynes]

I might have missed it somewhere but did you use the Autocom Twin Input Mixer which they describe as part#56?

Mine had exactly the same symptoms as yours and I solved it using the Autocom mixer.

[Tom B]

 

When I was MD of Autocom only about 15% to 20% of global customers wanted and purchased an isolation lead, and so for the 80% majority my expandable design actually saved both money and product size. Of course for the customers requiring an isolation lead, we went out of our way to help by providing a suitable lead, and also helping people understand why if was important to use them. I do not dispute that you may be able to buy a similar lead that is cheaper, but it will normally be cheaper for a reason, albeit that it has cheaper components or labour used, or perhaps because it is marketed direct at a predatory price without proper local distribution or dealer margins, and so will be at lower quality supply and support. That was the plan anyway!

 

[Joe Frickin' Friday]

...and also helping people understand why if was important to use them.

 

It's great that Autocomm provides such close support after the sale, but it would have been a lot better if there had been something in the owner's manual explaining it to people before they encounter problems or do damage. As EddyQ has noted, there are probably a lot of people who aren't bothering to contact Autocom for support - they're just motoring down the road grumbling about what a piece of crap their Autocom unit is. And worse, there are probably a number of people like guitardad who have actually damaged other devices. It's reasonably to expect the average person to know that they shouldn't stick their finger in a lamp socket; it's not reasonable to expect the average person to understand ground loops, isolators, and the possibility of damage if they hook these things up wrong.

[KDeline]

I know you tried to keep the cost down by making it basic at startup, but it can nickel and dime you to death after the initial purchase.

[Tom B]

Having been known as the owner of Autocom for so many years, I can understand people still thinking that I am Autocom when I give this support, but the fact is I am no longer Autocom, and so it is not Autocom who is providing this support, Tom Beman (ex-MD and original inventor of Autocom) is providing this support.

 

The product does what it says on the tin, (expandable system) and the instruction manuals do make it clear that you sometimes require isolation, when in doubt ask or use isolation.

 

If you go back some years, before people wanted to connect bike powered audio devices through their system, it was mainly portable bike to bike radio’s or portable music devices, and/or portable phones etc, which did not require isolation.

 

Isolation issues only really cropped up on bikes that had built in audio, such as Goldwings and some BMWs, and so I designed several Isolation leads for this purpose, then later GPS devices became popular so I developed Isolation leads for these. Now of course there are far more people buying systems and wanting to use many more bike powered audio devices through them, and so as the problem grew so did my input for better explanation. Just look at page 17 of the latest instruction manuals, and also page 23 of the brochure. PERFECTLY CLEAR!

 

The problem is not specific to Autocom and most other brands also require some form of isolation for their interface leads if the audio device used is bike powered.

 

I had developed the instruction manuals and brochure/website to help people understand this, plus provided substantial training to distributors to pass on to dealers and customers about this.

 

You start off with a basic system and only have to pay for parts you need, rather than having loads of parts, that many people don’t want, in a far more expensive kit,

 

Most customers understand respect and appreciate all that I did, and I had thousands of letters from very happy customers all over the world, so if you feel different I am sorry about that, but I won’t lose any sleep over an odd few customers, when so many others prove my efforts were good and well appreciated. That isn’t to say that I don’t care about the odd few that have some issues, and that’s why I am still offering my support, even though it if for a product/brand that is now owned by others.

 

The fact is that it is very easy to take things for granted, when for example I had thousands of door customers who all went away happy. The system and accessories do work well when used correctly, and I tried to develop the ways in which the products were described and sold and continually implemented improvements for support, and to help customers understand how to enjoy their products, but I always welcome constructive criticism like this.

 

IF I did it all again, with all that I have leant and now know, I am sure I would do some things different, and that even more people would enjoy the products I make, but I am sure there will still be the odd few that have a gripe.

 

As for costs, people want paying for what they do, including the dealers and distributors, and we all have to pay taxes, and what I made out of this was comfortable for me, (and very comfortable for the ex-wife!) But I was never what most would call rich, so I cannot agree that I over charged, but if we had cut out the distributor, and./or dealers margins it would have been by far the cheapest product out there, but US people for example prefer to buy from US dealers/importers, thinking they are safer and will get better support, so we had to include their margins when pricing, and unlike many mass produced (made in China for example) cheap parts, our parts were relatively low volume, higher quality parts and labour, and I never forced anyone to pay me anything for what I made. Like I said, most customers said they were very happy.

Tom

 

[flars]

I have two Autocom boxes. I had to put isolation on both of them, and went with non-autocom gli boxes from a reputable source (NOT radio shack, btw). They lasted less than a year - one only went 6 months. I then bought autocom gli, and they are still going 3 years later.

You ofttimes get what you pay for. Also, I found the notice about isolation in the manual BEFORE I installed the autocom, and when I put the XM on the bike I put the gli on at the same time because I read the manual.

[allikanbe]

I have 2 autocoms. I only need an isolator for one of them. It is a great system. Whatever I paid for each of them was money well spent. On my BMW, I have a Super Pro Avi connected to my zumo w/xm and mp3, cell phone, radar detector, and bike to bike via a kenwood. It really does not get any better. I also use Etymotic ER 6i ear phones. The autocom manages all of that stuff correctly.