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tram tr-50 problems


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#1 Lee Young

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Posted 07 July 2008 - 09:57 PM

I just bought a tram tr-50 lav mic. I got a really good deal on it and ended up spending only a hundred dollars on it. The problem is that it has a 2.5mm locking miniature plug which is not readily compatible with my sennheiser 100 series wireless mic system. My set-up is as follows:

sony pcm-d50--->beachtek dx-6--->sennheiser reciever (connects to beachtek by 3.5mm locking end to male xlr end)--->sennheiser transmitter--->magami 3.5mm to xlr cable
--->tram tr-50 xlr adaptor--->(connects to adapter via 2.5mm locking end) tram tr-50

The mic sounds wonderful when the tram xlr adaptor is plugged right into the beachtek, but when I use the wireless system with magami cable, there is a noticeable hiss. I know the wireless system is not adding noise because I've tried it with the supplied microphone that has a 3.5mm end. My only conclusion is that the magami cable is what's adding noise even though mogami cables have a wonderful reputation. The xlr adaptor is providing phantom power, but apparently the sennheiser does as well. Although when I take the battery out of the xlr adaptor the mic is no longer powered. I believe the wireless system only provides 5v and the tram mic requires more phantom power. The mogami cable is about a foot long. Here are my questions:

1. Should I cut off the 2.5mm plug and solder on a new 3.5mm plug to the tram tr-50, thus more or less making my xlr adaptor useless?

2. Should I get a shorter mogami cable to connect the power adaptor to the transmitter?

3. Are there just too many changes from a balanced to unbalanced signal going on here?

Any help will be greatly appreciated.
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#2 Hal Smith

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Posted 07 July 2008 - 10:34 PM

I just bought a tram tr-50 lav mic. I got a really good deal on it and ended up spending only a hundred dollars on it. The problem is that it has a 2.5mm locking miniature plug which is not readily compatible with my sennheiser 100 series wireless mic system. My set-up is as follows:
................Any help will be greatly appreciated.

I doubt if the plug mismatch itself is causing noise. The plug being wrong might create a connection with a lot of hum or static but not hiss.

I suspect there's a impedance and/or level match problem between the Sennheiser transmitter and the TR-50. Tram specs the TR-50 itself at 2,000 ohm nominal impedance and -57dB level. With the Tram TR-79 power supply the nominal output impedance is 250 ohms, from your description it sounds like you're using a TR-79. Look at specifications on Sennheiser's webpage for the Sennheiser mikes that match your transmitter and see what their nominal impedances are. If there's a 2 to 1 or more difference that could be your entire trouble.

According to Tram's webpage they can supply an array of different cable and plug combinations for TR-50's. You might try emailing them and see if they can advise you on purchase of one of their cables that will plug the TR-50 direct to your Sennheiser transmitter without the TR-79. You might get lucky and find that Tram's already had to figure out the TR-50 to Sennheiser interface.
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#3 Lee Young

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Posted 07 July 2008 - 11:32 PM

I have looked at the mke-2 mic that comes with my transmitter and there is more than a 2 to 1 difference. Here's the webpage http://www.bhphotovi...t_Lavalier.html.

Although, I just plugged my shotgun microphone directly into the sony pcm-d50 adaptor (3.5mm to xlr) with the mogami cable. There was a hiss. Then when I plugged the shotgun mic into the beachtek adapter via an xlr to xlr mogami, it was crystalk clear.

I don't quite understand what you are suggesting in regards to how to connect the tram into my wireless system. Are you suggesting that I send it to tram to have them put a 3.5mm end on it or are you suggesting that sennheiser or tram would provide me with a 2.5mm to 3.5mm adaptor. The reason I am hesitant to solder a 3.5mm end onto it is that it will make my tr79 useless. Anyways if you could possibly clarify that and respond to the second paragraph, that would be extremely helpful. And thank you so much for responding, especially as soon as you did.
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#4 Hal Smith

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Posted 08 July 2008 - 05:56 PM

Although, I just plugged my shotgun microphone directly into the sony pcm-d50 adaptor (3.5mm to xlr) with the mogami cable. There was a hiss. Then when I plugged the shotgun mic into the beachtek adapter via an xlr to xlr mogami, it was crystalk clear.

I don't quite understand what you are suggesting in regards to how to connect the tram into my wireless system. Are you suggesting that I send it to tram to have them put a 3.5mm end on it or are you suggesting that sennheiser or tram would provide me with a 2.5mm to 3.5mm adaptor. The reason I am hesitant to solder a 3.5mm end onto it is that it will make my tr79 useless. Anyways if you could possibly clarify that and respond to the second paragraph, that would be extremely helpful. And thank you so much for responding, especially as soon as you did.

You're welcome.

From the Sennheiser data sheets on B&H's website I'd say that you're fighting a rather large impedance mismatch problem. The input into Sennheiser transmitters is expecting a 50 ohm source impedance and you're hooking up the Tram TR-79 with a 250 ohm output impedance which could mean the Tram's output is getting heavily loaded down. That would tend to greatly reduce its output and as a result the Sennheiser transmitter's inherent noise becomes a problem. To say nothing of the fact that the Sennheiser transmitter is trying to send a phantom power supply voltage to the TR-79 which could be creating noise issues in itself.

Unfortunately, I'll bet money that there's no way to turn off the Sennheiser's phantom source like there would be on a mixer or preamp. As a last ditch, you could try inserting a small electrolytic capacitor in the center conductor lead of the TR-79's cable to the Sennheiser, the capacitor's plus (+) lead towards the transmitter. About 10uF @ 25 volts DC would be a good value to try. That will disconnect the Sennheiser's phantom voltage from the TR-79. You could rig up something temporary around Radio Shack cables, clip leads, and a capacitor around that value. The capacitor would go in the center wire of the TR-79's output cable.

My suggestion with respect to Tram was to email their technical support people and ask if they have any recommendations for interfacing their TR-79 to a Sennheiser transmitter. Be sure to give them the exact model number of your Sennheiser transmitter. The hope is that Tram's already had to figure out how to get their gear to talk to a Sennheiser transmitter without a noise problem.

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#5 Lee Young

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Posted 12 July 2008 - 02:42 AM

I've been talking to the people at Tram. My mic is negative bias or at least the power supply is. They said the only solution, if I were to have a positive bias mic, was to install a 3.5mm locking end. I'm pretty damn sure my mic is negative bias. Anyways until I hear back from them, I'm planning what I should do if my mic is definitly negative bias.

What is I used a ground lifter? would this eliminate the phantom power? I was thinking something like this: http://www.bhphotovi...rel_Ground.html

I also saw this: http://www.thebroadc......5SPRT-DC-20"

This seems like it might be perfect. My wireless system uses 3.5mm locking ends. Will it matter if its not a locking end.

Also, all these adaptors seem like they will add noise. Will they? Will these adaptors that disable the phantom power kill my frequency range? Thanks for all your help.
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