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Old 1st February 2013, 05:11 AM   #1
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Default Transformer secondary resistance

Can I get an approximate output value of a transformer based on secondary resistance? I have a Korg line mixer. The primary windinding weathered away and I can't access it. resistance on the secondaries is 3.7 to center tap for each lead. I found one in a CD player that seems to work but I don't know the voltage of the original. I am near certain that the transformer I tried is a little on the weak side.
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Old 1st February 2013, 05:35 AM   #2
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The secondary resistance should not vary with time and assuming a standard 600 ohm input would have little effect on any signal levels. Try using a constant line source with and without the transformer and see if the output levels change.
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Old 1st February 2013, 06:49 AM   #3
Mooly is offline Mooly  United Kingdom
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The secondary resistance has no real relationship to the voltage. 3.7 ohms could be many turns of thin wire or less turns of a thicker wire. Both would be 3.7 ohms, one giving (say) 20 volts AC and the other 6 volts AC.
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Old 1st February 2013, 06:56 AM   #4
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Thanks. I guess in a case like this, I look at the regulators and OP amps if I don't have schematic?
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Old 1st February 2013, 06:59 AM   #5
Mooly is offline Mooly  United Kingdom
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Like this,
Transformer specs for Dynaudio monitor
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Old 1st February 2013, 07:16 AM   #6
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That was very intuitive. That link answered quite a few questions. On my other desk I currently have some Older dynaudio drivers and bits and pieces of amplifier, crossover and power supply. Seeing that Dynaudio has followed every other Brand and their trends, I am glad that I opted against buying a pair. 10 years ago, Dynaudio Studio monitors were great but they are beginning to look like overpriced MP3 monitors like the Blue Skys I just sold.
Thank God for this forum! It makes true Hi fidelty attainable. I am also learning how to fix the broken stuff to keep the LoFi neighbors happy.
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Old 1st February 2013, 07:18 AM   #7
Mooly is offline Mooly  United Kingdom
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Pleased it helped
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Old 1st February 2013, 09:11 AM   #8
JMFahey is offline JMFahey  Argentina
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Quote:
I look at the regulators and OP amps if I don't have schematic?
Way to go.
That and power consumption.

Measured resistance can be used at most to distinguish "which is which" , and even so, it can still mislead you.
Say, you have a transformer for a small tube amp (say, a Champ), the HV winding will have, say, over 60 or 120 ohms DCR while the filament one less than 1 ohm.
Piece of cake

Now you have a transformer for a big SS amp: 40+40VAC for the main power amp, and 15+15V for the preamp.
The 80V winding will usually have *less* resistance than the 30V one , simply because the first one will be required to furnish, say, 5 to 10A while the second one may be happy with 100 mA.

And as a side note, low resistances are difficult to measure with precision ... unless you have a bridge or a dedicated meter.
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