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Extend freq audio xfmr

C

Conrad Ferrer

Jan 1, 1970
0
Is there any way, through the use of external components, to extend
the range at which an audio output transformer rolls off high
frequencies?

For example, when using an 8 ohm to 100V PA transformer for voltage
step-up, amplitude falls off at around 25KHz.

Conrad Ferrer
 
W

whit3rd

Jan 1, 1970
0
Is there any way, through the use of external components, to extend
the range at which an audio output transformer rolls off high
frequencies?

For example, when using an 8 ohm to 100V PA transformer for voltage
step-up, amplitude falls off at around 25KHz.

The low frequency performance of an audio transformer is maintained
by using a mass of high-permeability iron. To get higher frequency
performance, one uses thinner iron plates with insulating spacers
(just oxide layer on the plates, really) to prevent internal eddy
currents, or for very high frequency one can use powdered-iron
or ceramic (ferrite) cores.

But a ferrite that performs well into the RF range is more expensive
(and larger) than laminated-iron for a given power level. And this
is an OUTPUT transformer, power level is high. If you can
use biamplification (split off the woofer or subwoofer to a
separate output circuit) the low frequencies can be handled
with iron core, and high frequencies with whatever is appropriate.
If it all has to go through a single core, you might need to get
a custom-designed unit, or use something meant for switchmode
power supplies (and the specs won't include '8 ohm').
 
P

Phil Allison

Jan 1, 1970
0
"whit3rd"
Conrad Ferrer
The low frequency performance of an audio transformer is maintained
by using a mass of high-permeability iron. To get higher frequency
performance, one uses thinner iron plates with insulating spacers..


** That is totally wrong.

High frequency roll off in a wide band audio transformer is controlled by
the winding method - NOT the damn core material !!

A toroidal type or an E or C core shape where the primary and secondary
windings are multi-layered and interleaved will have wider bandwidth due to
reduced LEAKAGE INDUCTANCE .



......... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Conrad Ferrer"
Is there any way, through the use of external components, to extend
the range at which an audio output transformer rolls off high
frequencies?

For example, when using an 8 ohm to 100V PA transformer for voltage
step-up, amplitude falls off at around 25KHz.


** A judiciously chosen capacitor across the load may help extend the
response a bit.

You'll need a scope, square wave generator and drive amp to do the job.


........ Phil
 
P

Paul Mathews

Jan 1, 1970
0
Is there any way, through the use of external components, to extend
the range at which an audio output transformer rolls off high
frequencies?

For example, when using an 8 ohm to 100V PA transformer for voltage
step-up, amplitude falls off at around 25KHz.

Conrad Ferrer

You might find this useful:
http://www.rane.com/note159.html
Paul Mathews
 
P

Phil Allison

Jan 1, 1970
0
"Paul Mathews"


** I see it is your own article.

On a number of occasions, I have been was called on to diagnose amplifier
failures where the PA system installer simply had no understanding of "core
saturation " whatever. Nor at the time did a company called QSC.

The handbook for their USA850 and similar models directed owners and
installers to do what was almost certain to destroy the amplifier. Three
such victims were delivered to me with a " WTF happened ? " complaint.

The output device protection circuit fitted to most QSC amplifiers is not
capable of saving the amps if ever driven into a saturating transformer
load. The life expectancy reduces to a few seconds in this event.

The eventual fix was to install a 12dB /oct HPF with -3dB POINT @ 100Hz
internally in each channel and simultaneously make sure that no sub sonic
thumps were generated by the amps under ANY operating condition.

When contacted about the failures, QSC tech support were the OPPOSITE of
helpful.



........ Phil
 
W

Winfield

Jan 1, 1970
0
Phil said:
,
Conrad Ferrer asked,



** That is totally wrong.

High frequency roll off in a wide band audio transformer is controlled
by the winding method - NOT the damn core material !!

A toroidal type or an E or C core shape where the primary and secondary
windings are multi-layered and interleaved will have wider bandwidth
due to reduced LEAKAGE INDUCTANCE.

Correct, it's the use of special interleaved winding methods
to create low leakage inductance that wins the day, not core
materials, at high frequencies. But note, if we were talking
resonating inductors and high-frequency energy storage, why
then it'd be another matter entirely. Core losses would rule.

To answer Conrad, because it _is_ a leakage-inductance issue,
it's hard to externally correct the problem.
 
M

MooseFET

Jan 1, 1970
0
Is there any way, through the use of external components, to extend
the range at which an audio output transformer rolls off high
frequencies?

For example, when using an 8 ohm to 100V PA transformer for voltage
step-up, amplitude falls off at around 25KHz.

You can push it up a bit by boosting the level of the high frequency
signals going into the transformer. For normal sound there is very
little power above a few KHz so adding a boost starting at 25KHz won't
be a problem.

Are you driving the transformer from a low impedance such as a normal
audio power amplifier or a higher impedance? If the drive impedance
is low, the cut off will be where the leakage inductance as the same
impedance as the load. If your drive signal has a higher impedance,
you are likely to see a different cut off.
 
P

Paul Mathews

Jan 1, 1970
0
"Paul Mathews"


** I see it is your own article.

On a number of occasions, I have been was called on to diagnose amplifier
failures where the PA system installer simply had no understanding of "core
saturation " whatever. Nor at the time did a company called QSC.

The handbook for their USA850 and similar models directed owners and
installers to do what was almost certain to destroy the amplifier. Three
such victims were delivered to me with a " WTF happened ? " complaint.

The output device protection circuit fitted to most QSC amplifiers is not
capable of saving the amps if ever driven into a saturating transformer
load. The life expectancy reduces to a few seconds in this event.

The eventual fix was to install a 12dB /oct HPF with -3dB POINT @ 100Hz
internally in each channel and simultaneously make sure that no sub sonic
thumps were generated by the amps under ANY operating condition.

When contacted about the failures, QSC tech support were the OPPOSITE of
helpful.

....... Phil

Forgive the plug that follows, for what is quite possibly the lowest
leakage inductance PA transformer available commercially. It can be
seen here, accurately specified and conservatively rated:
http://www.rane.com/mt4.html
Unlike many PA transformers, this one was NOT designed according to
power transformer design rules. The balance of copper and core losses
and the winding design were entirely driven by audio fidelity and
power delivery considerations, including tolerance for amplifier
output DC offset. (Power transformer design rules place the emphasis
on minimizing cost within a temperature rise budget, which results in
poor audio performance.) End of plug. (I have no financial interest in
the manufacturer, a former client.)
Paul Mathews
 
P

Phil Allison

Jan 1, 1970
0
"Paul Mathews"
Forgive the plug that follows, for what is quite possibly the lowest
leakage inductance PA transformer available commercially.


** At the specified 20mH, it must be the worst on the planet !!
It can be
seen here, accurately specified and conservatively rated:
http://www.rane.com/mt4.html


** 20mH should be 20 uH - no ?

Unlike many PA transformers, this one was NOT designed according to
power transformer design rules. The balance of copper and core losses
and the winding design were entirely driven by audio fidelity and
power delivery considerations, including tolerance for amplifier
output DC offset.


** OK - 500 mohms is about double the usual value, plus the extra turns
pushes the saturation frequency lower. However, using a wound toroidal core
means that the limit is quite dramatic when it arrives. Still very bad news
for many power amplifiers - particularly QSC - that cannot take being
effectively dead shorted ,twice each cycle, at some low frequency while
delivering high power.

Pffffffftttt.......



........ Phil
 
C

colin

Jan 1, 1970
0
Conrad Ferrer said:
Is there any way, through the use of external components, to extend
the range at which an audio output transformer rolls off high
frequencies?

For example, when using an 8 ohm to 100V PA transformer for voltage
step-up, amplitude falls off at around 25KHz.

Conrad Ferrer

maybe you could have two transformers,
for different bands,
with the primaries and secondaries in series,
say a ferrite for high frequency wich becomes very low impededance at low
frequency
and so has no effect at low frequency where the iron tranformer does it all,
and maybe a capacitor accross the low frequency transformer prim and sec.

Colin =^.^=
 
J

Jasen

Jan 1, 1970
0
Is there any way, through the use of external components, to extend
the range at which an audio output transformer rolls off high
frequencies?

Negative feedback?
For example, when using an 8 ohm to 100V PA transformer for voltage
step-up, amplitude falls off at around 25KHz.

And that's a problem?

Bye.
Jasen
 
P

Paul Mathews

Jan 1, 1970
0
"Paul Mathews"


** At the specified 20mH, it must be the worst on the planet !!


** 20mH should be 20 uH - no ?


** OK - 500 mohms is about double the usual value, plus the extra turns
pushes the saturation frequency lower. However, using a wound toroidal core
means that the limit is quite dramatic when it arrives. Still very bad news
for many power amplifiers - particularly QSC - that cannot take being
effectively dead shorted ,twice each cycle, at some low frequency while
delivering high power.

Pffffffftttt.......

....... Phil

Hence the low-cut filter option available for most commercial power
amps. The Rane power amps monitor and limit their own volt-seconds
output.
Paul Mathews
 
P

Phil Allison

Jan 1, 1970
0
"Paul Mathews"
"Phil Allison"
Hence the low-cut filter option available for most commercial power
amps. The Rane power amps monitor and limit their own volt-seconds
output.


** You really are totally clueless - aren't you ?

You think in dumb clichés and post opinionated drivel.


" > It can be seen here, accurately specified and conservatively rated:

** 20mH should be 20 uH - no ? "


** Cat got your tongue on this point ???




....... Phil
 
W

whit3rd

Jan 1, 1970
0
"whit3rd"

High frequency roll off in a wide band audio transformer is controlled by
the winding method - NOT the damn core material !!

A toroidal type ... will have wider bandwidth due to
reduced LEAKAGE INDUCTANCE .

In fact, it's six of one, half dozen of the other.
When the core material is slightly conductive, eddy currents
exclude the flux (by Lenz's law) and that means the flux, since
it is not in the core, is not constrained to link the primary and
secondary windings. The presence of unlinked flux is the
definition of leakage inductance.
 
P

Paul Mathews

Jan 1, 1970
0
"Paul Mathews"
"Phil Allison"









** You really are totally clueless - aren't you ?

You think in dumb clichés and post opinionated drivel.

" > It can be seen here, accurately specified and conservatively rated:

** 20mH should be 20 uH - no ? "

** Cat got your tongue on this point ???

...... Phil- Hide quoted text -

- Show quoted text -

Thanks for noticing that typo. Yes, 20 microHenry. Font error: should
have gone to a symbol. Thanks for the insults, too, I'm honored. Can't
go long without a good insult from crazy Phil.
Paul Mathews
 
J

John Popelish

Jan 1, 1970
0
Paul said:
Thanks for noticing that typo. Yes, 20 microHenry. Font error: should
have gone to a symbol. Thanks for the insults, too, I'm honored. Can't
go long without a good insult from crazy Phil.
Paul Mathews

I suspect a measurable fraction of that 20 uHy might be just
in the loop area of the lead wires to the connector,
especially if the wires happen to be spread out a bit more
than in the pictures. I think that pair should be twisted.
 
P

Phil Allison

Jan 1, 1970
0
"Paul Mathews"

** You really are totally clueless - aren't you ?

You think in dumb clichés and post opinionated drivel.

The world has far too may deadshits like you already.

Go drop dead.



........ Phil
 
P

Phil Allison

Jan 1, 1970
0
"John Popelish"

I suspect a measurable fraction of that 20 uHy might be just in the loop
area of the lead wires to the connector, especially if the wires happen to
be spread out a bit more than in the pictures. I think that pair should
be twisted.


** Can you spell the word " F A N A T I C " for me - John ?



....... Phil
 
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