Re: audio transformer, about 30W size, easily available?


"Pooh Bear" <rabbitsfriendsandrelations@xxxxxxxxxxx> wrote in message
news:42EE1FD6.6E39722D@xxxxxxxxxxxxxx
>
>
> BFoelsch wrote:
>
> > "Pooh Bear" <rabbitsfriendsandrelations@xxxxxxxxxxx> wrote in message
> > news:42ED88D1.242CA476@xxxxxxxxxxxxxx
> > >
> > > BFoelsch wrote:
> > >
> > >> "Pooh Bear" <rabbitsfriendsandrelations@xxxxxxxxxxx> wrote in message
> > >> news:42ED6249.D87912CE@xxxxxxxxxxxxxx
> > >> > mw wrote:
> > >> >
> > >> >> Hi,
> > >> >>
> > >> >> Know of any easily available (inexpensive and stocked) 30W audio
> > >> >> transformer to couple to an 8 ohm speaker?
> > >> >>
> > >> >> I am experimenting with a custom audio amplifier design that uses
> > >> >> tranformer coupling rather than the usual capacitors. I took a
gamble
> > >> >> and tried to use a power transformer, but that's not working well
> > >> >> because they are designed to work well at 60 Hz and the ones I've
> > >> >> tried
> > >> >> roll off very fast at higher frequencies. This isn't an
audiophile
> > >> >> project, but I want something a little better.
> > >> >>
> > >> >> I want something I can get at a place like DigiKey or Newark or
> > >> >> Mouser,
> > >> >> not from a custom house or scrounging at hamfests or one of those
> > >> >> "classic tube audio transformers" that go for $100. I can't use
the
> > >> >> little audio transformers sold in Digikey because their power
handling
> > >> >> is too small.
> > >> >>
> > >> >> Would one of those 70V PA distribution transformers work for this?
Is
> > >> >> there a PA transformer vendor with real spec sheets, not just a
> > >> >> catalog
> > >> >> ad?
> > >> >
> > >> > You don't say what the primary side drive is - i.e. tube or
transistor.
> > >> >
> > >> > If it's transistor and you want and you want something like a 1:1
> > >> > transformer
> > >> > you can pretty much forget it unless you want to pay for a custom
wound
> > >> > job.
> > >> > There's simply no market for such things.
> > >> >
> > >> > 70V transformers are designed to be loaded with quite a high
> > >> > impedance -
> > >> > no
> > >> > good for 8 ohms.
> > >>
> > >> Could you clarify this for me? Exactly what impedance should they be
> > >> loaded
> > >> with?
> > >
> > > It's calculated from first principles.
> > >
> > > If it's 30W you want and the voltage is 70V then I = W/V = 30/70 = ~
0.43
> > >
> > > Zl = V / I = 70 / 0.43 = ~ 163 ohms
> > >
> >
> > Yes, but you are calculating the impedance that the transformer places
> > across the 70 volt line. You specifically state that
> >
> > >> > 70V transformers are designed to be loaded with quite a high
> > >> > impedance -
> > >> > no
> > >> > good for 8 ohms.
> >
> > What do your calculations do to support your point? You haven't
mentioned a
> > single word about the transformer load (secondary winding) other than to
say
> > that it must be other than 8 ohms.
>
> No I'm talking about the secondary ! The primary is unknown until the OP
gives
> some data.
>
> > What does the reflected primary impedance
> > have to do with the optimum secondary load, and why are 70 volt
transformers
> > no good for 8 ohm loads?
> >
> > I'm still confused. Why can't a transformer with a 167 ohm primary be
> > designed to match an 8 ohm speaker?
>
> No you twit ! That's the *SECONDARY* load impedance / voltage ! 160 odd
ohms
> isn't 8 ohms. Do you know nothing ?
>
> Are you the original OP btw ?
>
> Graham

Oh, you are talking about the transformer that DRIVES the 70 volt line.
Everybody else is talking about the transformers that connect the 70 volt
line to the speaker.


.

Loading