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Does anyone know if I can use a Quam TBL 25 volt 4 watt audio transformer to step down 120 volts to 12 volts, later to be rectified to a 12 volt dc power supply? I know 12 volt power supplys are normally cheap and easy to come by, but in my current situation I have very few components to work with hence the unconventional application. Any tips or cautions would be greatly appreciated.

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  • \$\begingroup\$ 12 volts AC on the secondary usually produces a voltage (after rectification) of about 15 volts DC. Please provide a data sheet link for the transformer too. \$\endgroup\$
    – Andy aka
    Apr 9, 2020 at 10:48
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    \$\begingroup\$ If you mean it has a 25V primary to be fed with 120 VAC then almost certainly not. If it Links would helpusually has about 25VAC across it then 120 VAC would destroy it promptly. \$\endgroup\$
    – Russell McMahon
    Apr 9, 2020 at 10:48
  • \$\begingroup\$ Description for various versions here. The TBL25 expects 25 VAC at audio frequencies. No go at 110 VAC. IF the power requirements were low then a suitable capacitor in series with the primary may allow some sort of a 12 VAC output. Or not. \$\endgroup\$
    – Russell McMahon
    Apr 9, 2020 at 10:52

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It would not be advisable to do that. With the audio transformer not having been designed for the purpose, its possible that its winding would get burnt with 120V~ applied across it.

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Does anyone know if I can use a Quam TBL 25 volt 4 watt audio transformer to step down 120 volts to 12 volts

The data sheet says that the maximum primary voltage is 25 volts: -

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In addition to this it specifies that the frequency response is 100 Hz to 15 kHz.

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  • \$\begingroup\$ Thanks everyone for the help. If anyone happens to know the wire gages and winding turns on a primary and secondary needed to render 12vac from 120vac, and if the core material would matter, please let me know. \$\endgroup\$ Apr 9, 2020 at 14:13
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    \$\begingroup\$ @ChrisFouroseven it totally depends on how much current is going to flow and that, in turn depends how much power your load requires. The core material and size matter plenty and the size affects the number of turns. A bigger core needs fewer turns than a smaller core. The core of the audio transformer is, almost certainly not big enough to get the required turns to operate on 120 volts with some tricks. \$\endgroup\$
    – Andy aka
    Apr 9, 2020 at 14:26
  • \$\begingroup\$ also, honestly, transformers that have the same power rating as yours but are 120V-safe are single-digit dollar or euro costs; almost certain you don't want to do this yourself, because it will end up being more expensive and less good. It's really hard to imagine a situation where you can self-wind a useful transformer, but can't buy a finished 12V one. Maybe you want to describe that situation in the question itself. \$\endgroup\$ Apr 9, 2020 at 15:47

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