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Sonotrim: Positive or Negative Bias?

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Hi All, 

At the risk of sparking derision from the veterans, I have three Sonotrim lavs (all with external powering units with battery compartments). How can I know whether they are positive or negative ground when run through lectro wireless units, in order to ensure that they are not out of phase? I also have an equal number of TRAM 50's also with external units, some with battery compartments, some without. The question would also extend to these mics, and mixing them with the sonotrims.

Thanks

RL

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Positive bias lavs have the ground and bias wire connected to the ground (pin 1) and the audio wire to pin 3 in a TA5 connector. Negative bias lavs have the ground and bias feed connected to pin 3 and the audio feed connected to the ground. Try mixing both types together and listen for any difference if any.

 

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without opening the connector - i believe newer trams have a red band to signify positive bias. Negative bias would not have anything. 

Older trams used to have a little mark on the head (opposite grill side) that had either a + sign for positive bias or nothing (possibly a - in some cases?) to show negative bias. 

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On 19/09/2017 at 12:05 PM, Zach R said:

without opening the connector - i believe newer trams have a red band to signify positive bias. Negative bias would not have anything. 

Older trams used to have a little mark on the head (opposite grill side) that had either a + sign for positive bias or nothing (possibly a - in some cases?) to show negative bias. 

 

 

Yeah, on the older ones there is a little moulded plastic indent on the back that will either have + sign or nothing to designate what bias it is. There is also an 'in-between' model as well. Older ones had the circle, newer ones have the red band... but the 'in-between' model requires you to open the connector and physically see how it is wired. 

 

I have some of both, but haven't actually used them yet side by side. I imagine just holding them together in your had will give and speaking while listening will give you a fair idea if they are in phase. Doing it will panning them hard left and right will help! 

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Thanks for the replies. Further digging revealed this information: 

 

Lavalier Power Supplies
Lavalier Power Supplies come in a couple of different varieties.  Some require you to use an internal battery, some require phantom power (12VDC, 48VDC or either), and some work both ways either with a battery or phantom

         Tram Negative Bias Power Supplies:   Will operate only with the internal battery
 
         Tram Positive Bias Power Supplies: Will operate with either the internal battery or 12-48VDC Phantom Power.

With Tram power supplies the positive bias version is the most versatile (giving you the option to use a battery or phantom power), but it is also a little more expensive.

 

So if the TRAM power supply will not work with phantom power it must be negative bias.

http://www.trammicrophones.com/sale/general/bias.asp

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