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Making a balanced output for MixPre 6-II - which Lundahl transformer


Mungo
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Hello,

 

for a ultra light setup I had the idea to convert a MixPre 6-II into an eng mixer. It surprisingly performs absolutely well with 1 or 2 camera hop transmitters and even a wireless camera return. Unbalanced out but no rf noise struggle at any time, at high level output though (+6dBu).

 

But when using the audio output for serious wired applications that little unbalanced 1/8 inch jack is just not suitable enough. So I want to build a small and light passive kind of DI box permanently connected to the mixpre for the bag. The 1/8 jack could stay connected forever and probably held tight by a 3D print.

I found no DI boxes on the market that are handy enough for the bag. Yes, there's the Neutrik NA2M, but it only handles up to -3dBu.

 

I found this: https://www.lundahltransformers.com/wp-content/uploads/datasheets/SIB15.pdf

which might be right ok. But still a little too bulky and way too expensive. The manual of the SIB15 says that there a only two Lundahl LL1532 transformers built in, which can be purchased as a solo component too: https://www.lundahltransformers.com/wp-content/uploads/datasheets/1532_1593.pdf

But when you google the LL1532, many sources call this is Mic level transformer which I don't want. I want to go out unbalanced from the MixPre with +6dBu.

 

Do I need the LL1531 https://www.lundahltransformers.com/wp-content/uploads/datasheets/1531.pdf instead? Or why are the 2x LL1532 in the SIB15 capable up to +12dBu, in the LL1532 datasheet 6dBu less? I'm quite confused, which ones should I order? They are not cheap at all so I don't want to spend money for trial and error.

 

Thx in advance!

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I very strongly recommend that you ask the folks at Lundahl.  I had a similar need some years ago, wishing to use Jensen transformers.  I was able to get an "audience" with Deane Jensen himself, and armed with the schematics of all the devices he made a recommendation which was not the trafo I was originally looking at.  His recommendation was great and we used that box on nearly every job for years.  Ask the makers themselves!

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  • 2 weeks later...
24 minutes ago, The Documentary Sound Guy said:

If it's like the other Radial boxes, that's going to be awfully heavy to add to a bag setup.  I love my Radials, but they're not light!

It weighs 250 grams, so I guess that is why they call it a "Bug" and not a "Turtle" 😀

 

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On 1/22/2022 at 10:04 AM, New Alighieri said:

I’d love to hear how this develops!

 

They didn't reply, so I went on with my research.

I will switch over to Neutrik NTL 1 which is way easier to buy here. Also it's more versatile (600/10k) and its pins match with standard universal circuit boards.

Due to other projects this will take some time, but I'll keep you informed.

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  • 1 month later...
  • 1 month later...

News to this thread:

 

It works well, very well, at first impression. No distortion, no noise, quite clear and rich sound. I can't say much about the exact output level and about low frequency respsonse. That will take some time for examination and I will write it down here.

When switching parallel to a camera hop transmitter (Sony DWT-B01N), there is a slight level drop (about 1-2dB), but still good sound.

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