BeePre Input Transformer Modification

[fullheadofnothing]

Well, a while ago PB and I did a photoshoot for the input transformers to give a balanced input to the BeePre. The plan always was to get it up on the website, rather than as a pdf manual. A few things came up here and there (like a full replacement of the website), and now it's finally up. It's in the blog section of the website, or here is the link.

http://bottlehead.com/bee-pre-input-transformer-modification/

[Demsy]

Hi Josh,

It says 404 Page Not Found. Is it removed?

[fullheadofnothing]

It got lost in the recent website shuffle. I've put it back now.

[Demsy]

Thanks Josh!

[bombay317]

I am going to be following your instructions. 

I contacted Cinemag, and they have 4 week lead times on the transformers (if anyone was interested to know that).  I opted for the double shielded ones. 

Mouser ships immediately, but they always do that.  Another option would be Digikey or Jameco, but all of that stuff is usually in stock by the 1,000s.

[bombay317]

When I went through this I noticed a difference between the BeePre mod and the BeePre XLR procedure.

https://bottlehead.com/bee-pre-input-transformer-modification/ in this there is no step to tie Pin 1 of the XLR input to the chassis ground. 

There is a step covered in the BeePre manual at the first step of "Output Wiring" that ties Pin 1 of the XLR input to the chassis ground.

Should this be done for this input?

[Paul Birkeland]

It's not unreasonable to put a switch into the BeePre to make this connection.

[bombay317]

Paul,

I am not sure I follow your comment.  Are you saying you should put a switch in between Pin 1 and the XLR shield?  I'm trying to understand what you mean.

In the data sheet http://cinemag.biz/line_input/PDF/CMLI-15-15B.pdf for the CMLI-15/15B2 under the "TYPICAL APPLICATION" section, there is a switch installed from Pin 1 to ground, but it is also in parallel to a R and C.  Not sure if that is what you meant?

I really just followed the "BeePre Input Transformer Modification" by Joshua Harris.  These XLR inputs take the place of R3 and L3 and do use the green and brown pairs that go to the input switch.

[Paul Birkeland]

Sure, you can follow Cinemag's documentation.  One position gives a hard ground to the load end of the shield, while the other position looks to provide a convenient path to ground for high frequency noise.

The BeePre we used for those photos is mine, and I haven't noticed any noise on the balanced input, but I use my BeePre in a pretty quiet environment with short cables.

-PB

[grufti]

The link to the page describing the input transformer modification is dead again. I would like to take a look at it. Is it still possible to revive that page one more time?

[Deke609]

You can use "Way Back Machine": http://web.archive.org/web/20170716200138/https://bottlehead.com/bee-pre-input-transformer-modification/

[Brissie]

This link shows the full set of pictures: https://web.archive.org/web/20150929102753/http://bottlehead.com/bee-pre-input-transformer-modification/