ALOT of Coupling Transformers?

[Barry Reise]

Can anyone suggest a supplier that stocks ALOT of audio coupling
transformers?

I am looking for something outside of the standard values.

In particular 16R primary, with secondary somewhere in the range of
50R-100R.

I am using the low end of the band, so these resistances would be more
like at DC (via DMM) than the usual 1KHz.

Thanks for any pointers.

Or ... if I need to wind my own, what type of core is suitable for a
manual hand winder, and available through the usual outlets?

Barry Reise

 

[Phil Allison]

"Barry Reise"

Can anyone suggest a supplier that stocks ALOT of audio coupling
transformers?

I am looking for something outside of the standard values.

In particular 16R primary, with secondary somewhere in the range of
50R-100R.

I am using the low end of the band, so these resistances would be more
like at DC (via DMM) than the usual 1KHz.

** You post makes very little sense.

You must specify the frequencies and power level involved and if you need
isolation between the input and output.

Or better still, say what you are trying to do.


.... Phil

 

[Phil Allison]

"Robert Macy"

Can anyone suggest a supplier that stocks ALOT of audio coupling
transformers?

I am using the low end of the band, so these resistances would be more
like at DC (via DMM) than the usual 1KHz.

The 'gotcha' is going ot be that low cutoff frequency. 10Hz not so
bad, but even going down to 1 Hz,


** The OP asked for an "audio" transformer - so the lowest frequency is
20Hz.

Let him say if it is otherwise in his app.



.... Phil

 

[Barry Reise]

the max turns ratio you will need to match worst case 16 ohm to 100
ohm is 2.5:1 which is not too uneven.

The 'gotcha' is going ot be that low cutoff frequency. 10Hz not so
bad, but even going down to 1 Hz, you will need 1.25 to 2.5H on the 16
ohm side. That can be a lot of turns depending. Going down to 0.1 Hz
just makes it 10 times worse.

Thank you for your reply.

The "DC" referred to measurement of the winding resistance via DMM,
not an impedance meter. IOW it was not the lower freq limit.

Some "audio" transformer will do 10Hz, but 20Hz would be OK. Top end
2KHz. 10W power rating. Apart form the 16R pri and 50/100R sec, that's
all that matters.

I am really looking for a supplier who has a wide range these things
off-the-shelf. If not, I would need to source a type of core I can
wind myself without industrial equipment.

The suggestion to use the secondary of a mains transformer is
something I had looked into. But a center-tap is not going to provide
complete isolation. And completely split secondary windings are
usually equal resistance, ie 12-0-12V. This does not provide the
desired ratio.

Barry

 

[Phil Allison]

"Barry Reise"

Some "audio" transformer will do 10Hz, but 20Hz would be OK. Top end
2KHz. 10W power rating. Apart form the 16R pri and 50/100R sec, that's
all that matters.

** The 953-0398 toroidal tranny from Element 14 is all you need.

Twin 115 volt primaries and twin 25 volt secondaries with a 50VA rating at
50 Hz - wire the primaries in parallel and the secondaries in series to
get 115V to 50V.

Scale that down to 20 Hz and the relevant voltages change to 46V to 20V.

For 10 watts at 16 ohms you need 12.6 volts - so 20 gives a nice margin.

A cheaper alternative is the similar E core 178-0860 - this will be less
good at high frequencies and draw far more magnetising current.

You pays your money and takes your choice ....



.... Phil

 

[Phil Allison]

"Robert Macy"


Keyword is 'might work', because many of those AC mains transformers
have their performance peak at 50/60Hz and purposely reduce higher
frequencies.

** Most are good to a few kHz and toroidal types work well out to 50kHz or
more.


Worse, they're usually higher coercivity material [since
with AC mains the 'signal' is always there] which means that if used
for audio the transformer disappears at low signal levels,


** Absurd nonsense.



.... Phil

 

[[email protected]]

What is the EXACT URL for "...953-0398 toroidal tranny from Element
14..." ?

http://au.element14.com/multicomp/mcta050-25/transformer-50va-2-x-25v/dp/9530398?Ntt=953-0398

Or http://goo.gl/8ZPp0 avoids linewrap.

Grant.

 

[Phil Allison]

"Robert Macy"

What is the EXACT URL for "...953-0398 toroidal tranny from Element
14..." ?

** It's Farnell under a new name.

http://au.element14.com/



.... Phil

 

[Barry Reise]

A cheaper alternative is the similar E core 178-0860 - this will be less
good at high frequencies and draw far more magnetising current.

You pays your money and takes your choice ....

OK, they're on my Christmas list.

And why did they ever change their name from Far--nell to
El--e--ment--four--teen? I thought electronics guys were smart.

Barry

 

[Phil Allison]

"Robert Macy"
"Phil Allison"
"Robert Macy"

Keyword is 'might work', because many of those AC mains transformers
have their performance peak at 50/60Hz and purposely reduce higher
frequencies.

** Most are good to a few kHz and toroidal types work well out to 50kHz or
more.

Worse, they're usually higher coercivity material [since
with AC mains the 'signal' is always there] which means that if used
for audio the transformer disappears at low signal levels,

** Absurd nonsense.

Why do you say "** Absurd nonsense." ??


** Because no such effect exists.

Consider that the laminated cores used in the vast majority of AC power
transformers and audio output transformers the same - ie silicon steel,
grain oriented or possibly not.

Toroidal AC power transformers all use grain oriented silicon steel, the
exact same cores are used for audio applications.

You need to test some REAL transformers if you still think everyone is
wrong.


.... Phil

 

[Tim Williams]

Why do you say "** Absurd nonsense." ?? Even new materials in audio
transformers have some coercivity to them and require a certain amount
of 'energizing' to 'wake up' the magnetic material.
(...)
Drive transformer using an audio source at 300Hz. Vary the amplitude
of the source uniformly in time. Watch the signal that gets through
the transformer. As you turn the amplitude down, you will find a
'nonlinear' transfer function as the coercivity of the transformer
comes into play.

Only if you're operating in the low frequency limit where inductance is
critical. Generally, where mu_r is over a thousand under all conditions,
it's high enough not to notice.

To be precise, coercivity isn't the property that produces this effect,
because coercivity is measured with a fully saturating waveform. Small
signal effects occur in their own (very small) hysteresis loops. However,
the physical mechanism ("sticky" magnetic domains) is the same.

As for frequency response, Phil is correct about toroidials -- they are
good enough to have been used in some fairly involved tube amplifiers.
The leakage is small enough that lots of NFB can be used (cathode
feedback, global, etc.) while maintaining the high bandwidth (~50kHz).

Tim

 

[Phil Allison]

"Tim Williams"

As for frequency response, Phil is correct about toroidials -- they are
good enough to have been used in some fairly involved tube amplifiers. The
leakage is small enough that lots of NFB can be used (cathode feedback,
global, etc.) while maintaining the high bandwidth (~50kHz).

** The OP will of course complain that those are specially made
ransformers - just like E-Core types used in tube amplifiers are specially
designed with many layers of winding sandwiched together to reduce leakage
inductance.

OTOH - my comment was about regular, off the shelf AC power transformers.
I have tested any number of them and at least in the step down role,
bandwidth is around 100kHz.

Another plus is the extremely low magnetising current - right up until
saturation begins. Means distortion products will be completely negligible
long as the saturation limit is not reached.

The only drawback is sensitivity it DC current in the windings, so tube
balance in push-pull output stages is critical.



.... Phil

 

[John Doe]

"Barry Reise"


** You post makes very little sense.

Do your really think so, Philly?
--