How-to Identify Tram TR50 Microphone Bias

On a recent recommendation from a friend, I decided it was time to purchase a decent lavalier mic for shooting video. Trying to stretch the budget as usual, I wanted an industry standard mic that I knew would be available at a reasonable price and that I could easily rent more of locally if needed. With that in mind, I was confident a Tram TR50 would fit the bill.

As I started skimming eBay for options, I noticed a number microphones and power supplies TR79 that were listed without mentioning if they were wired for positive or negative bias. Even more interesting was how much less the unmarked components were selling for than their more thoroughly examined counterparts.

I know in the past I’ve had moments of panic & disbelief as multiple lavs on a shoot didn’t work when first hooked up, only to remember the bias voltage and find that some of the power supplies and mics had been mixed up.

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In an effort to shed some light on the topic for anyone looking to buy, sell or just use a Tram TR50 mic effectively, I’ve put together this short video on how to identify positive vs. negative bias wiring in both the mics and power supplies. I also recommend reading this Bias Article from The Broadcast Shop along with Audio Technica’s blog post on the topic for more in-depth information.

I feel compelled to clarify that up until this point I have been shooting all of the videos for this channel on a shoe-string budget, making the most out of used shotgun microphones that I found on eBay. While I use high quality microphones daily for professional work, those are either provided by the production company or rented in specifically for each task. As a result, my need for owning high-quality lavalier microphones has been non-existent in recent years. When trying to get setup to shoot decent video, forking out $200 to $500 for a single mic just wasn’t in the budget.

As you’ll see in the video, the TR50 I ended up buying on eBay was unfortunately damaged. The seller was great and issued a refund right away, so I’m back to the drawing board shopping for a Lav for this channel. I’d love to hear your suggestions for what you would choose if you had to find a lav that meets my specifications, let me know in the comments!