I do not want to explore why or why not power supply toroids
will work as audio output transformers.
I would like to know how to translate power supply toroid
specifications into audio transformer specifications.
For instance how would one convert these specs:
http://www.toroid.com/standard_transformers/rectifier_transformers/DataSheets/701.062_M4.pdf
Into this context:
VTP15671-1100 - Firefly Push Pull Output Transformer 22.5k to 8 ohms 1.5 watts
And vice-versa
will work as audio output transformers.
I would like to know how to translate power supply toroid
specifications into audio transformer specifications.
For instance how would one convert these specs:
http://www.toroid.com/standard_transformers/rectifier_transformers/DataSheets/701.062_M4.pdf
Into this context:
VTP15671-1100 - Firefly Push Pull Output Transformer 22.5k to 8 ohms 1.5 watts
And vice-versa
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determine the turns ratio of the power transformer.
then look up the formula that relates turns ratio to impedance ratio.
that will get you in the ball park.
it will NOT tell you if you have sufficient primary inductance or if you have enough turns in the primary to handle the current, nor will it tell you if you will have any voltage breakdown issues... and tells you nothing about DC imbalance nor leakage inductance and capacitance issues...
then look up the formula that relates turns ratio to impedance ratio.
that will get you in the ball park.
it will NOT tell you if you have sufficient primary inductance or if you have enough turns in the primary to handle the current, nor will it tell you if you will have any voltage breakdown issues... and tells you nothing about DC imbalance nor leakage inductance and capacitance issues...
pri magnetizing current should be on most pwr xmfr datasheets - can calc Lm
valid only for specified line V, freq VT product - pwr xfmr core often working into saturation - 2x increase in VT can give 10x increase in Im
conversely if you can operate at lower V (VT really) the reduction in Im is similarly disproportionate
pwr xfmr cores are not gapped, don't tolerate DC bias current - use push-pull only
valid only for specified line V, freq VT product - pwr xfmr core often working into saturation - 2x increase in VT can give 10x increase in Im
conversely if you can operate at lower V (VT really) the reduction in Im is similarly disproportionate
pwr xfmr cores are not gapped, don't tolerate DC bias current - use push-pull only
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No. It's related to the "< 2mA" on the power transformer datasheet. You don't need to know this to calculate the parameters you have asked for. If you don't want to know whether the transformer is suitable for purpose, that's up to you.
There is insufficient information in the power transformer datasheet. The turns ratio is, near enough, the unloaded voltage ratio, but you only have the loaded ratio. To calculate one from the other you need the regulation, which isn't given. It could be approximated from winding resistance, but that's not given either. Some power transformers have more infomative datasheets. If you knew the turns ratio, it's really not hard to find out how to calculate the impedance ratio.
The rated primary current, at a known voltage, provides for a rough estimate of maximum power before meltdown. I trust you know how to calculate power, given a current and a voltage.
Forget this nasty little toroid a substitue for the VVT Firefly transformer.
What you want to know is the impedance ratio is the square of the turns ratio.
There is the text 'Uo=8.1V RMS' in the spec, this may well be the unloaded secondary voltage. This makes the regulation about 25%. The temp rise of 63 degrees C seems high as well.
Assuming you connect the secondaries in parallel and 234V in gives 8V out then the turns ratio is 29.25 and impedance ratio is 855.5 An 8 Ohms speaker load will give Ra-a = 6.84K which is way too low.
What you want to know is the impedance ratio is the square of the turns ratio.
There is the text 'Uo=8.1V RMS' in the spec, this may well be the unloaded secondary voltage. This makes the regulation about 25%. The temp rise of 63 degrees C seems high as well.
Assuming you connect the secondaries in parallel and 234V in gives 8V out then the turns ratio is 29.25 and impedance ratio is 855.5 An 8 Ohms speaker load will give Ra-a = 6.84K which is way too low.
So ............
((234/unloaded out)^2)*8 ~ primary Z ?
I'm not trying to replace the 1 example with the other,
just to find a method of calculation ........... Thanks
> determine the turns ratio of the power transformer.
> then look up the formula that relates turns ratio to
> impedance ratio.
Then when an output xfmr is speced @ 8 Ohm output Z
and 5 kOhm primary Z, those numbers are based on having
a 8 Ohm load rather than something intrinsic to the xfmr ?
> then look up the formula that relates turns ratio to
> impedance ratio.
Then when an output xfmr is speced @ 8 Ohm output Z
and 5 kOhm primary Z, those numbers are based on having
a 8 Ohm load rather than something intrinsic to the xfmr ?
So ............
((234/unloaded out)^2)*8 ~ primary Z ?
I'm not trying to replace the 1 example with the other,
just to find a method of calculation ........... Thanks
Yep, you got it!
Yes and no. That's why some are hesitant about just giving answers without an explanation of why.
Intrinsic to an output transformer is a filter with a pass band barely adequate to fit the audio band in. An audio transformer has not only the right impedance ratio, but also puts its barely adequate pass band in the right place for its specified loading. A good one will optimise Q and properly balance the two halves for PP.
So, those numbers are based not just on having particular load, but also on the frequency of operation. Theoretically for a mains transformer, worst case scenario, the numbers are only true for the specified mains frequency. In practice for a toroid they will be true over a broad band but probably not broad enough, and it will have a full-amplitude low frequency of just a few Hz below specified. Q could be anywhere, and if the halves are matched they will not be so across the bandwidth.
For an audio transformer, if you change the loading, you shift the pass band sideways.
All these things and more make the answer to your questions yes or no, depending. 8:1 impedance ratio is very different from 8k:1k. Only the turns ratio is the same.
The reason you get hassled with stuff you don't want to know is perhaps because "impedance ratio" is a misnomer, in that it's not just a ratio. It's a relationship between one specified impedance and another, for a particular pass band.
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