Autocom Ground Loop Isolator - A reduction in volume question?

[adventuredon]

Hi all, I have a Garmin nuvi 765 on my bike. No other devices connected to confuse anything. I am getting engine whining interference when it is connected (increases in noise when I switch bike on). Been so since about day one!

I have checked connections all around
I have changed where autocom and where GPS is earthed
I have re routed the wires to autocom
I have changed where gps gets positive from
I have held autocom unit away from bike-no dice
I have tried re routing garmin wires--no dice.

Nothing changes except when I disconnect my power to the GPS unit and run it on it's own battery. Then the interference goes away 100%. Autocom support agree with me that it's the power lead to the garmin that causes the noise.

Autocom advised that it probably needs a ground loop isolator. Autocom ones are £40 plus £7.50 postage! So I thought I'd try and see if that is the hassle without losing £7.50 to return the package if it doesn't work! So I bought an isolator from an AV shop for £8 and bingo, it removes all the interference. But my volume is now reduced by about 25%, so much so that when I press a function on the GPS, the 'Ping' noise is not even heard (might even be that nav instructions don't come through as I tried it static). It also stops sound getting to my pillion headset when connected via my audio channel. So far from perfect.

So I guess my question is, do all ground loop isolators reduce the volume when removing interference?
Or is the Autocom isolator special that it won't reduce the volume? Will be changing and ordering on Monday, but if they all do this, I might not bother.
Any suggestions
Cheers

 

[AberdeenAngus]

Unless the isolator has an amplifier stage then some loss in volume is inevitable.
You can tell if it has an amplifier as it will need a separate 12v supply.

 

[adventuredon]

Ok it doesn't have power, nor does the more expensive autocom one...hmmph

 

[newboy]

Speak to Sam at Chainspeed - he will explain and sell you the best product

 

[adventuredon]

Cheers, will do.

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[newboy]

Sam Wray

Chainspeed Ltd
Tel: 01994 484428
[email protected]
www.chainspeed.co.uk

 

[Roadrash Rider]

The Autocom isolated leads will also drop sound level. That's unfortunately how they work. One other thing to check do both the Autocom unit and GPs unit have isolation / noise filters off the supply? Also poor connections on the jack plug (3.5mm) also introduce noise and or reduced volume.


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[adventuredon]

Spoke to Sam today. No benefit at all in buying the more expensive autocom isolator. They all work the same. I do need to check that both GPS and autocom are grounded at the same place. Ordered a new 3.5 mm cable today as it felt a bit perished at head end. Will update as I progress.

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[Roadrash Rider]

Spoke to Sam today. No benefit at all in buying the more expensive autocom isolator. They all work the same. I do need to check that both GPS and autocom are grounded at the same place. Ordered a new 3.5 mm cable today as it felt a bit perished at head end. Will update as I progress.

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Do you have a mains filter to your Autocom unit (on the 12v feed) and the GPs?


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[adventuredon]

No.

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[Roadrash Rider]

No.

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No guarantee but if you fit an autocom mains filter and feed the Autcom and GPS from it would / should clear any mains interference being picked up. These faults are a pain in the arse to find, but you said when the GPS was batter fed no pick up which might be mains interference, worth a try.


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[adventuredon]

Do you have a mains filter to your Autocom unit (on the 12v feed) and the GPs?


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Me bad, looked today and yes it is there. 12v, little box wired in at source.
OK so today I put both earth's in the same location, changed the 3.5mm lead - this seems to have eliminated the humming interference in my helmet without the need for an isolator. However, the interference remains in the pillion headset. But she is so seldom on the bike I am not worried about it/her!
Only think I get now and again is a crackle and pop! But there was someone on a mobile close by so not sure if that has any effect. Time will tell how irritating the crackle gets, but for now I am satisfied that the interference has been sorted. Need to go on a long run though to make sure. So all in all, a £1.99 stereo 3.5mm cable has solved my problem. I think!

 

[adventuredon]

now sorted with a newer garmin unit