NTE10/3 + shielding can= usable mic input transformer?

Hi everybody!

I want to build two mic preamps with fet input opamp in the first gain stage, the schematic asks for jensen jt115-ke which are over my budget for now, so could I use, as placeholders, the mentioned and (recently discussed http://groupdiy.com/index.php?topic=63432.0) cheapo neutriks, provided additional shielding?
I think so, since the impedances are 200:50k (wired as 1:10 ratio) and the frequency range is 20hz-20kHz. Max. input -6dB (not great but ok, I think).
Apart from the subjective sound which is hard to predict, would this be a technically correct replacement or have I overlooked something important, like dc resistance etc.?

Thank you for any hint or comment!

datasheet
https://www.monacor.com/de-de/monacor/produkte/beschallungstechnik/signalverarbeitung/signaloptimierung/nte-10-3/?r=pdf
can
http://uk.farnell.com/oep-oxford-electrical-products/a262can/screening-can-transformer/dp/1172345?ost=OEP&selectedCategoryId=&categoryId=700000096003&searchView=table&iscrfnonsku=false

Preamp schematic (for reference, not to be discussed in this thread)
http://www.recordingmag.com/resources/resourceDetail/332.html

This transformer is probably made for exactly this purpose. -6dB max input is not bad at all for a 1:10 (!). You'll want pre-trafo-attenuation anyway for very-high or line signals (look at e.g. ISA110, V76, G9).

Try it - how wrong could it go?

And make sure to report here in full details about your findings.

Jakob E.

  I did used it in a mic pre but without shielding and it was noisy. It did sound fine, one of those and a 5534 and you already have a nice preamp. I used it in a few prototypes including a tube preamp, I think it was an altec, this last sounded really nice for voices but again too noise to use as is. Again, I use no shielding and it was sharing the enclosure with 3 ugly power trannies.

JS

gyraf said:

This transformer is probably made for exactly this purpose. -6dB max input is not bad at all for a 1:10 (!). You'll want pre-trafo-attenuation anyway for very-high or line signals (look at e.g. ISA110, V76, G9).

Click to expand...

Just what I wanted to hear!

gyraf said:

And make sure to report here in full details about your findings.

Click to expand...

Seems the internet is full of famous last words, promising just that... Let´s say I mean to!  ;D

joaquins said:

  I did used it in a mic pre but without shielding and it was noisy. It did sound fine, one of those and a 5534 and you already have a nice preamp. I used it in a few prototypes including a tube preamp, I think it was an altec, this last sounded really nice for voices but again too noise to use as is. Again, I use no shielding and it was sharing the enclosure with 3 ugly power trannies.

Click to expand...

Even more of what I wanted to hear! The posted can is a true mu-metal shield, and also available from farnell even cheaper! I´ll go that way. Though I´ll keep eyeing those Jensens. :

Thanks!

Although mu-metal is the good stuff, don't underestimate the shielding effectiveness of good old-fashioned magnetically-soft iron when there's enough of it. Take for example iron water pipe (as available in building-repair-shops) - you can get short pieces of iron pipe and screw-on endcaps for cheap (as traditionally used for improvised bombs) - and this will do very good magnetic shielding.

(just don't scare anyone with it, it'll be looking dangerous..)

Jakob E.

gyraf said:

- you can get short pieces of iron pipe and screw-on endcaps for cheap (as traditionally used for improvised bombs) - and this will do very good magnetic shielding.

Click to expand...

And that pipe inside a larger one with foam as a spacer should attenuate really well, might come out to near X-attn^2, with endcaps on both inner and outer. And it would be really easy to mount in a chassis with hardware store type pipe hanger clamps, if you have the room for this.

(just don't scare anyone with it, it'll be looking dangerous..)

Click to expand...

True, a pipe nipple with two endcaps, and wires coming out of one, or both ends like there is a multi-layer football shaped spherical compression charge within, is probably not advisable in your carry-on luggage.


OT: Last time I was at the airport, there was a vulture with two dead squirrels in his mouth trying to get on the plane. They stopped him at the gate:

"Sorry sir, only one carrion per passenger".

Gene

gyraf said:

(just don't scare anyone with it, it'll be looking dangerous..)

Click to expand...

How do you not scare someone with something like that?

I'm going to have to disagree with you on this one. I don't recommend using pipe pieces in your electronics projects. Get a proper EMI shield.

80hinhiding said:

Anyone else here try these input transformers?

Adam

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I think the shielding cans that come as accessories only shield five of the six sides. Jensen/Sowter/Cinemag etc shield all 6 sides with only small holes for the connections. You really do need to shield all six sides to stop interference getting in.

Cheers

Ian

The ones I've used in the past for OEPs had bottom pieces with holes for the OEP pins. 

diytubes from the blackmarket has them with bottom shield...

audiogeeks1 said:

The ones I've used in the past for OEPs had bottom pieces with holes for the OEP pins.

Click to expand...

OEP are beginning to make some nice transformers with proper shielding. Definitely worth considering as an alternative.

Cheers

ian

What about a tube nipple and some caps, shielding such small transformer shouldn't be a problem! Core material permeability and hysteresis is vital as trying to archive the same nominal parameters with lower quality core would bring parasitics to the roof, for the shield you could have a very thick wall of whatever iron you have around and get away with it, as long as it fits inside your project.

I'd used them in the past and the only real complaint is interference, of course is not a world class transformer but a nice option considering the price.

JS