Ground loop Quest / Autocom

[trebor]

Well, I've managed to test my ground loop isolator by connecting it at each end of the lead between the Zumo and Autocom and guess what?
Well, it certainly reduces the volume but there is no difference, that I can tell, between the volume levels no matter which end of the cable it is connected. To be honest I was expecting a reduction in volume no matter which end it was connected (there is no amplifier in the lead and, as you don't get anything for nothing, there are bound to be some losses as the signal passes through the transformers) but I was expecting a difference in volume level when the isolator transformers were reversed.

I think I will have to take the isolator to work with me and set it up on a scope and see what it is doing, see if there really is a 1.3dB gain built into it.

I also checked the continuity of the negative line of the Zumo cradle audio output socket to the Negative terminal on the battery; it looks like the cradle uses an independent earth on it's audio output so, if both devices are bike powered, then an isolating lead should be used.

Bob

 

[mr_magicfingers]

Well, I've managed to test my ground loop isolator by connecting it at each end of the lead between the Zumo and Autocom and guess what?
Well, it certainly reduces the volume but there is no difference, that I can tell, between the volume levels no matter which end of the cable it is connected. To be honest I was expecting a reduction in volume no matter which end it was connected (there is no amplifier in the lead and, as you don't get anything for nothing, there are bound to be some losses as the signal passes through the transformers) but I was expecting a difference in volume level when the isolator transformers were reversed.

I think I will have to take the isolator to work with me and set it up on a scope and see what it is doing, see if there really is a 1.3dB gain built into it.

I also checked the continuity of the negative line of the Zumo cradle audio output socket to the Negative terminal on the battery; it looks like the cradle uses an independent earth on it's audio output so, if both devices are bike powered, then an isolating lead should be used.

Bob

Got a chance to do the same test yesterday and came to the same conclusion. Either the 1.3db gain is insignificant or it's just not there at all. Will have to live with it and just get the volumes of the various bits of kit set so they match.

J.

 

[trebor]

I set the Isolator up on a test rig last night, I put a 50mV, 1kHz, signal into the 'Out' cable and monitored what came out of the 'In' cable. I got a 55mV signal out, if my math is correct this is a 0.4dB gain.

Just to verify it I reversed the signal direction (i.e 50mV in to the 'In' cable) and got 43mV out, a loss of 0.6dB.

Both the left and right channels gave the same result. Not quite the 1.3dB advertised

However, as I stated in an earlier post, I thought the volume was reduced with this device in line. The reason I saw an increase in level on the test bench is probably due to the high input and output impedance of the test equipment when compared to that of the Zumo and Autocom, both of which will have much lower impedances.

Therefore, IMHO, if you connect the device at the Autocom end of the cable (i.e. with the 3.5mm jack from the isolator plugged into the Autocomm and the lead from the Zumo plugged into the 3.5mm socket of the isolator) then you should get the best results. This is the opposite way to what I thought it would be based on the 'In' and 'Out' labelling on the box.

Bob

 

[mr_magicfingers]

Therefore, IMHO, if you connect the device at the Autocom end of the cable (i.e. with the 3.5mm jack from the isolator plugged into the Autocomm and the lead from the Zumo plugged into the 3.5mm socket of the isolator) then you should get the best results. This is the opposite way to what I thought it would be based on the 'In' and 'Out' labelling on the box.

Bob

Nice to see the actual stats on it, thanks for testing that. I'm now using a PAC isolator from the US and have it plugged directly into the autocom box with the feed from the gps into the isolator. This is now giving me much better volume and quality and means the levels are on a par with other things plugged in.

 

[trebor]

I'm now using a PAC isolator from the US and have it plugged directly into the autocom box with the feed from the gps into the isolator. This is now giving me much better volume and quality and means the levels are on a par with other things plugged in.

Interesting, if the volume is insufficient whan I try this out I may look into getting one of them. Have you any links to it?

Bob

 

[mr_magicfingers]

Can't remember where I actually got mine from, just googled and found somewhere that would ship from the US, might have been through ebay but this is the unit

http://www.sonicelectronix.com/item_8987_PAC+SNI-1-3.5.html

They do one with rca connectors which you obviously don't want, but not all ads show that clearly, so just a heads up on that.

J.

 

[trebor]

Thanks for that.

It looks pretty much like, if not identical to, the one I have already, certainly the specs are the same.

Does it look the same as the one you previously bought off Ebay? If so it may be manufactured/designed differently to produce better results.

Bob

 

[mr_magicfingers]

I haven't cracked them open to compare, but the PAC device feels better quality, better and heavier cable and connectors, box seems better sealed etc. It certainly seems to do the job better to me, and gives better results than the cheaper ebay one I had.

 

[trebor]

So there is a difference by the sounds of it. I'll have to think about getting one of those if mine isn't up to it.

Thanks again.

Bob

 

[scots_jon]

I set the Isolator up on a test rig last night, I put a 50mV, 1kHz, signal into the 'Out' cable and monitored what came out of the 'In' cable. I got a 55mV signal out, if my math is correct this is a 0.4dB gain.

Your math is not correct...

 

[trebor]

OK, what is the gain then?

 

[scots_jon]

OK, what is the gain then?

0.8db. Because you are working with voltages and not powers the calculation is 20*log(V1/V2).

Cheers,
Jon.

 

[trebor]

0.8db. Because you are working with voltages and not powers the calculation is 20*log(V1/V2).

Cheers,
Jon.

So it is, my excuse is its 30 odd years since I was at college and I normally just work in power!

Cheers

Bob