# A transformer is a transformer...

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#### Externet

How to translate an audio transformer specified as 1300Ω to 8Ω with no turns or voltage ratios to be used in a higher frequency custom power supply; and the reverse; how to translate a typical 60 Hz transformer specified as 120V primary to 12V secondary to be used in higher audio-range frequency custom circuitry ?

And there is also the transformers specified by their inductance windings... with no more data to discern nor published by vendors.
I wish they would be unified in their published specifications.

#### barry

What do you mean "translate" a transformer? Do you want the turns ratio when you know the impedance ratio? That's

n=sqrt(Zpri/Zsec)

- - - Updated - - -

What do you mean "translate" a transformer? Do you want the turns ratio when you know the impedance ratio? That's

n=sqrt(Zpri/Zsec)

#### FvM

##### Super Moderator
Staff member
Winding ratio, main and leakage inductance, windings resistance and current capability, saturation flux are the relevant parameters. Depending on the transformer application, only part of the parameters is specified, the remaining parameters have to be derived from known application properties or need to be measured.

#### Externet

Thank you, gentlemen.
Translating a transformer specifications given as -say 1300Ω primary to 8Ω secondary- into how many volts primary to how many volts secondary ratio. And the reverse.
What are the equations involved ?

#### schmitt trigger

Remember the basic transformer equations:
the voltage ratio is directly proportional to turns ratio
the impedance ratio is proportional to the square of the turns ratio

Your impedance example above would have a 12.7:1 turns ratio.

#### c_mitra

Translating a transformer specifications given as -say 1300Ω primary to 8Ω secondary- into how many volts primary to how many volts secondary ratio. ...
Insufficient information.

it does not appear to be a power transformer. It is more like a voltage transformer with a fixed step down ratio that is given some where else. You can guess the power handling capacity by looking at the size and the frequency range by looking at the core.

Please excuse me because that is rather crude. If you do not have the datasheet, you will need to do some experiments- real measurements.

#### FvM

##### Super Moderator
Staff member
Barry did the translation of impedance to winding ratio in post #1. More can't be done for the time being.

What do you particularly mean with "higher audio-range frequency custom circuitry"?

For a power audio transformer, the turns per volt have to be calculated according to the minimal frequency, e.g. a 20 Hz to 20 kHz transformer needs threefold turns per volt than a 60 Hz transformer. In addition it needs interleaved multi-section windings to achieve low leakage for sufficient high upper frequency corner.

#### Externet

Thank you, gentlemen.
The formula posted by Barry cleared the question. The square root of the impedances ratio is the turns ratio.

...What do you particularly mean with "higher audio-range frequency custom circuitry"?
As in designing a power supply that works with 2KHz AC into the transformer.

#### dick_freebird

Used to be a lot of little audio transformers in this
range, before good power amplifier ICs capable of
direct driving 8-ohm speakers were common. 8 ohm
to 1Kohm center tapped seemed especially common.

I suspect the usual laminated E-core is not great
for higher frequencies, but 2kHz is probably in the
sweet spot for such an audio transformer (not
especially high).

c_mitra

### c_mitra

points: 2

#### c_mitra

Used to be a lot of little audio transformers in this range, before good power amplifier ICs capable of direct driving 8-ohm speakers were common. 8 ohm to 1Kohm center tapped seemed especially common....
They really used to be small (in size) and had considerable DC resistance and the primary use or objective was (i) DC blocking or isolation and (ii) impedance matching (for speakers). You are right about the frequency range but I guess it may be working upto 5kHz (I am just guessing). They were very common in small transistor radios.

The impedance ratio to turns ratio relation will break down if the resistance component is significant part of the impedance. I guess the impedance ratio at 50Hz and 2kHz will be grossly different.

#### FvM

##### Super Moderator
Staff member
I suspect the usual laminated E-core is not great for higher frequencies, but 2kHz is probably in the sweet spot for such an audio transformer (not especially high).
It's possible though. If I understand right, you are asking about a 2 kHz-only, not a wideband audio transformer. Flux will be downsized to compensate for higher losses, e.g. half of the 50 Hz transformer. Gives still 1/20 turns per volt.

Cut-tape core with thin (e.g. 0.1 mm) lamination would be preferred.

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