Balanced input transformers

[xcortes]

I'm thinking I'll mostly use my BeePre through the single ended inputs but since I'll have an extra available input and also have the balanced output of the repro I'll convert one input to balanced. If I want a 600 input and the attenuation network is 50k I'm assuming 600:50k transformers is what I need. How about these?

http://db.AudioAsylum.com/mhtml/m.html?forum=magnequest&n=8918&highlight=kardon&r=&search_url=%2Fcgi%2Fsearch.mpl%3F

I already have a pair courtesy of Keto.

[Doc B.]

No that will step up the signal too much. You want a 1:1 ratio that has an impedance somewhere in between, like 15K/15K. Something like a Cinemag 15/15 series, with the threaded chassis mount and fly leads would be ideal. That's the type of transformer mounting the chassis is set up for.

[Paul Birkeland]

Hello Xavier,

With the 600 ohm output impedance of the Repro, that sets the lower limit for the input side of the input transformer.  On the other side of the transformer will be the attenuators, which have an impedance that ranges down to around 50k on the input side.  While you could use a 50k:600, the transformer would give you some serious step up and potentially come across as being noisy.

What ends up being most agreeable is a 10k:10k or 15k:15k transformer, with a resistor across the primary to match the attenuator load better to the transformer setup.  

In the Bee Pre, we currently have a pair of 10mm holes in the jack field that will allow for a variety of different input transformers from different vendors.  Some examples are:

Sowter 3575 (specify mounting style E)
Cinemag CMLI-15/15B (specify 3/8" stud)
Jensen JT-11P-1 (specify 3/8" stud)

There are some other low budget input transformers that are open (unshielded), but one would expect some serious roadblocks in implementing these.

Note that we have not tested any of these options (yet), and that we may offer our own iron for this spot if the price to performance of the above offerings leave us wanting more.

-PB

[xcortes]

I just had an experience with the 437A amp (you have mail) where a pair of old Triad trafos blasted a pair of Jensens. That's what started me thinking about this.

I have a pair of MQ Ni B7s. I'd need to figure out how to physically place them them but I guess they would be killers if 10k:10k is the spec.

[Paul Birkeland]

Yeah, I would recommend sticking some double sided tape to them, then trying them in various positions and orientations.  You may be able to drill a couple of extra holes up front on the chassis and stack them up there, well away from the power transformer. 

The list of transformers I wrote is sort of in order of "gut feeling" on how they'll perform.  I was actually pleasantly surprised to see that the Sowters aren't obscenely expensive,

[xcortes]

Of course the B7s would be single ended, not balanced, but who's counting?

[Bas Horneman]

Of course the B7s would be single ended, not balanced, but who's counting?

So are the Cinemags doc recommended. That is how you actually make something balanced. See attachement for a balanced connection.

[Paul Birkeland]

If top performance is desired, the Sowter is the best candidate.  You can shoot them an e-mail, and let them know that you are interested in a pair of 10k balanced input transformers for a preamp, but that they must mount on a 3/8" or 10mm threaded stud.

I had a model picked out when we released the BeePre, and I believe it was the 3575.

A Magnequest B7 could be tried, but they are large and unshielded, and consequently a bit of an inconvenient gamble.

-PB

[Bas Horneman]

A Magnequest B7 could be tried, but they are large and unshielded, and consequently a bit of an inconvenient gamble.

Actually the high nickel version of the B7 is impervious to humm.

Translated from Dutch to English:
http://translate.google.nl/translate?sl=nl&tl=en&js=n&prev=_t&hl=nl&ie=UTF-8&u=http%3A%2F%2Fwww.audio-creative.nl%2Fhifi%2Fdddac-1794-nos-diy-dac-deel-5%2F2%2F

[Paul Birkeland]

Having had hands on experience with small signal nickel Magnequest iron (and open frame nickel transformers from other winders), I would disagree.

-PB

[Bas Horneman]

 

Having had hands on experience with small signal nickel Magnequest iron (and open frame nickel transformers from other winders), I would disagree.

Did you also use the Hi-Nickel versions? I'm asking because in my previous post that I linked to the B7 high nickel was more impervious to hum than the Lundahl LL1690 which is also shrouded in a mu-metal enclosure. As usual in audio (as far as I am concerned) the devil is in the details.

Bill Whitlock of Jensen wrote:
" It should also be noted that higher permeability core materials are more immune to external fields. Therefore, an unshielded

[Paul Birkeland]

usual in audio (as far as I am concerned) the devil is in the details.

Bill Whitlock of Jensen wrote:
" It should also be noted that higher permeability core materials are more immune to external fields. Therefore, an unshielded