Jump to content


Photo

Input Impedance Tbp12 Beltpack When Pin 4 Tied To Pin 3

tbp12 impedance

  • Please log in to reply
17 replies to this topic

#1 merlijnv

merlijnv

    Just Startin'

  • Members
  • Pip
  • 2 posts

Posted 04 May 2014 - 01:00 PM

Hi Everybody,

 

 

The manual of the TBP12 beltpack states that the input impedance is 1,3 MOhms. According to the same manual the impedance is lowered when pin 4 is tied to pin 3 in the TA4F connector. Does anyone know the value of this impedance?

 

 

Regards,

 

 

Merlijn van Veen


  • 0

#2 merlijnv

merlijnv

    Just Startin'

  • Members
  • Pip
  • 2 posts

Posted 07 May 2014 - 03:09 AM

Ok my unit has arrived today and I measured an unloaded impedance of 20 kOmhs when pin 4 (Z) is tied to pin 3 (signal). Seems reasonable. Correct me if I'm wrong?

 

 

Regards,

 

 

Merlijn


  • 0

#3 dboomer

dboomer

    Line 6 Staff

  • Moderator
  • 2765 posts

Posted 07 May 2014 - 06:04 PM

Correct ... 20k

#4 tccc

tccc

    Just Startin'

  • Members
  • Pip
  • 49 posts

Posted 18 May 2014 - 04:18 AM

Hi all,

 

I've been going through our mics soldering 3 and 4 together in the connector, which seems to help solve the distortion problem we were getting during loud scenes.

 

Just a thought though... seeing as we're never going to use the TBP12s for anything other than mics for theatre applications, is it feasible for us to open the packs and solder 3 and 4 together at that end instead? Saves having to do it every time we buy a new mic - none of the off-the-shelf TA4-terminated mics that I've come across so far have had 3 and 4 tied in the connector.


  • 0

#5 dboomer

dboomer

    Line 6 Staff

  • Moderator
  • 2765 posts

Posted 18 May 2014 - 07:04 AM

Well you would be on your own ... But ... The jack is a snap in assembly in the beltpack. So theoretically you could modify an assembly and snap it in. You could also experiment with a small series resistor between pins 3&4 to change the level.

http://www.fullcompa...uct/405558.html

#6 tccc

tccc

    Just Startin'

  • Members
  • Pip
  • 49 posts

Posted 18 May 2014 - 07:14 AM

Thanks Don. I've got one pack with a poor battery connection that keeps turning itself on and off, so I'll take a look at the input jack whilst I've got it apart. 


  • 0

#7 tccc

tccc

    Just Startin'

  • Members
  • Pip
  • 49 posts

Posted 20 May 2014 - 03:20 PM

It was actually a nice easy modification in the end, as you can just solder the two pins together on the reverse of the input assembly. As an aside, I also smeared non corrosive silicone-based sealant around the input assembly, and on the RF board (especially where it sits very close to the main PCB). End result... the high-pitched whine I was getting at mid-high gain from the beltpacks has now completely disappeared - they're finally completely silent!


  • 0

#8 dboomer

dboomer

    Line 6 Staff

  • Moderator
  • 2765 posts

Posted 20 May 2014 - 06:08 PM

What mics are you using?

#9 tccc

tccc

    Just Startin'

  • Members
  • Pip
  • 49 posts

Posted 20 May 2014 - 07:32 PM

Countryman B3 & B6s, and some Sennheiser MKE-2s


  • 0

#10 dboomer

dboomer

    Line 6 Staff

  • Moderator
  • 2765 posts

Posted 21 May 2014 - 06:32 AM

Did you get the Line 6 versions by Countryman? They add a small resistor across pins 3&4 which is similar to shorting the pins. You can check out their wiring scheme on their web page. Don't worry about the Zener diode. It's just an added protection ( but probably unnecessary)

#11 tccc

tccc

    Just Startin'

  • Members
  • Pip
  • 49 posts

Posted 21 May 2014 - 09:17 AM

Hi Don,

 

We've got the SL (Shure) versions - Countryman said there was no difference between the SL and L7 (Line 6) wiring, and certainly on their website the wiring diagram is identical.

 

Are you not thinking about the 4.7k resistor across pins 2 and 3?

 

We've had an issue with the B3 & B6 capsules (red and blue-band) distorting during loud musical theatre scenes, especially when they're positioned on the cheek (although we've experienced it in the hairline position too). It sounds more like digital clipping or limiting than microphone distortion. I've not quite been able to get to bottom of it yet - it seems intermittent. The Line 6 specs say to tie 3 and 4 for lavalier use and leave them open for instrument use, which isn't how most TA4 shure-wired mics seem to be from the factory.

 

I'd been through all of our B3 mics and soldered 3 and 4 together, and the next show I did was perfect. However we had the problem again with 2 out of the 14 systems we were using on a show last week. They started off fine, but after the first few scenes the distortion appeared. The same thing happened on the second rehearsal with different capsules, so we ended up having to patch in some analogue Sennheiser systems for those cast members instead.

 

I'm not sure what to try next. Judging by the TBP12 specs, it should be impossible to overload the inputs no matter how loud the cast sing! The receiver audio LEDs never get much further than 2 or bars, and I've never seen the red clip light on the beltpacks either. Puzzling!


  • 0

#12 dboomer

dboomer

    Line 6 Staff

  • Moderator
  • 2765 posts

Posted 21 May 2014 - 12:15 PM

Oops ... typo :)

 

You have to hit the front end of a TBP12 with 6 vac p-p to cause it to hard limit.



#13 tccc

tccc

    Just Startin'

  • Members
  • Pip
  • 49 posts

Posted 21 May 2014 - 12:21 PM

That's what I thought... which isn't going to happen with a microphone! Very strange.


  • 0

#14 dboomer

dboomer

    Line 6 Staff

  • Moderator
  • 2765 posts

Posted 21 May 2014 - 02:22 PM

Not unless you are micing a jet engine ;)



#15 tccc

tccc

    Just Startin'

  • Members
  • Pip
  • 49 posts

Posted 21 May 2014 - 05:07 PM

That's not in the show yet as far as I know ;)

 

I'll pay closer attention to the mics during next week's show, and hopefully at least work out what factors change between the channels that do distort and the ones that don't. I've tied pins 3 to 4 on every beltpack now anyway to lower the resistance. Didn't notice any difference in level whether those two are connected or not though.

 

If nothing else, I'm at least now very familiar with the insides of those beltpacks, especially the little battery cover springs!


  • 0

#16 dboomer

dboomer

    Line 6 Staff

  • Moderator
  • 2765 posts

Posted 22 May 2014 - 09:49 AM

:D



#17 sdevino

sdevino

    Line 6 Staff

  • Product Management
  • PipPip
  • 109 posts

Posted 22 May 2014 - 11:39 AM

Are you using Red Band B3 and B6 mics? Those are the low sensitivity versions normally used for musical theatre. 


  • 0

#18 tccc

tccc

    Just Startin'

  • Members
  • Pip
  • 49 posts

Posted 22 May 2014 - 02:47 PM

The B3s we have are all red-band versions, and the B6s are blue-band, which are even less sensitive. 


  • 0





Also tagged with one or more of these keywords: tbp12, impedance

0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users