[LAU] OT: isolating transformers, redux

[Folderol]

On Tue, 28 Dec 2010 02:35:47 -0800
Ken Restivo <ken at restivo.org> wrote:

> On Wed, Dec 22, 2010 at 07:49:26AM +0000, Folderol wrote:
> > On Tue, 21 Dec 2010 22:10:07 -0800
> > Niels Mayer <nielsmayer at gmail.com> wrote:
> > 
> > > Jensen has some really good application papers talking about audio
> > > transformers. By induction, one might get an idea of why they cost so
> > > much -- same reason why other "pro" stuff with a reputable name also
> > > costs a lot.
> > 
> > <snip>
> > 
> > I think some people are totally missing the point. The O/P has already said he
> > doesn't want to spend a lot of money as the kit he's connecting to is only of
> > moderate quality.
> > 
> > I don't know if the links I suggested to Ken are any good (whether he's able to
> > buy from those people) but I asked 'someone who knows'(tm) about these things
> > and was told that the 'Oxford' transformers are more than adequate for the job.
> > 
> 
> Thanks!
> 
> Yes, I obtained a pair of cheap telephone isolating transformers from Radio Shack. And it works! Yay! US$8 total.
> 
> It is indeed specced for 300-5000Hz, but it seems pretty flat when run with a short (1 foot or so) wire. But, I'm noticing a lot of high-end rolloff with a 20-foot wire. Are there any components I could add to combat this?
> 
> Since I have the magic of JAPA handy, perhaps I'll actually measure its frequency response. Nice to have great (free) tools available for this stuff.
> 
> -ken

Put the transformers on the end of the wire furthest from the laptop output.
You'll then get the full benefit of the laptop's low output impedance. Also, if
it is an actual headphone socket on the laptop that you are using, put 47ohm
resistors across the primaries of the transformers. This will dampen line
inductance and capacitance effects. Sometimes you can also improve the response
by putting resistors across the secondaries of the transformers - I know that
sounds counter-intuitive. You would have to play about with the values as it
depends very much on the transformer characteristics.

-- 
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.