Electrical – Two line 220V to 12V AC and 5V DC power supply for valve amplifier and MP3 radio

amplifierswitch-mode-power-supplytransformer

I need 12V AC out for a valve preamplifier and a 5V DC out for a MP3 radio.

valve preamp: Fever 6J1 tube preamp amplifier

mp3 radio: DC 5V Micro USB Power Supply TF Radio MP3 Decoder Board 5V Audio Module for Car Remote Music Speaker

My first Idea was to build a very simple supply with a classic transformer as you can see in the picture.

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I make some calculations and to be sure to have enough power I should use a 12V 20W transformer (12V 0.8A valve amp and 5V 1.5A MP3 radio).

A classic metal core transformer is heavy and too big for my project, so I was thinking to use a LED driver 0-50W 11.5V AC output for example ETZ50 0-50 W ZAMEL. (sorry stack don't let me to put the link)

I have some doubts about this solution.

  • will work only few minutes?
  • is good for power applications?
  • the output is a square or sine wave?
  • the design of the circuit can smooth enough the output signal to avoid MP3 damage?
  • if the LED driver is not a good solution how is possible to power the device using a switching transformer? (classic transformers are outdated)

Best Answer

An LED driver is simply the wrong pick. These are typically constant current supplies, and what you need is constant voltage.

There's literally thousands of constant voltage switch mode power supplies out there; go to mouser.com, or farnell.com or digikey.com or any other reputable distributor and pick an AC/DC supply suiting your needs;
do not just buy anything off ebay, amazon or aliexpress; you'll get a bad supply with loads of noise, unless you have someone who stands with their reputation for the noise data they have in their datasheet. On ebay etc, you typically don't even get a datasheet. That's like asking to be scammed.

For max cost-efficiency: get a laptop power supply, and build a simple supply from whatever that delivers (typically, something like 18V–20V) (if you're doing this as a prototype: look at ti.com, find the simple switcher modules, ask for samples).

Your MP3 player probably won't care about switching noise at all, but your Valve amplifier might be a bit sensitive, but to which frequencies is impossible to tell. As a rule of thumb, use a DC/DC converter with a high switching frequency and a use sufficient ferrite beads, filter caps if you hear noise on the output even when there's no sound playing.

What I often see in low-noise applications is that you'd do something like:

  • Pick a relatively beefy 13 VDC switch mode supply
  • Use a linear voltage regulator to bring the voltage down to a nicely noise-compensated 12VDC for the amp
  • For the MP3 player, your 13V->5V linear regulator approach works well enough if the player in question doesn't draw too much current. Else, simply use a switch mode power supply 13V->6V and a linear LDO regulator, too.

This would be very nicely adaptable to the laptop power supply approach. Clear advantage: nowhere in the system do you get in contact with grid voltage, making it much harder to kill yourself, or start a fire that won't be covered by insurance.

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