TheRadioBoard

[journeyman]

Just to show you my latest project, partly inspired (or rather accelerated) by Dave's latest trafo project.
In a second hand shop I bought a large 230V to 3-12V switchable power supply for about 1 buck. Tore out the rectifiers, and put in a 1/4" headphone switch, a 250K potmeter+0.1uF cap, on both sides some speaker connectors from an older radio set, and voilá, a nice looking switchable headphone transformer. The 3-12V switch now functions as 25K to 350K ohm input switch for serial connected 2x32ohm headphones.
Some images:

I'll have to open it up once more, and set up the polarity switch as a 'serial/parallel' switch to allow for 64/16 ohm switching for phones to have even more leeway in impedance matching.

[wireguy]

journeyman, what a clever idea. I am always amazed at the ingenuity of you folks across the pond.
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What would our world be like, if Tesla was alive in our time?

[Dave-N2DS]

That is excellent! I like that.

Some of the surplus parts sellers do offer wall wart transformers with a
220 volt primary. I think that would be much better than the 110 volt
that we have.

This can be very beneficial for those that have a budget to adhere to.

Dave
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Please visit my website at: http://www.makearadio.com

[macrohenry]

And you have a polarity inverter for the audiophiles!

Macrohenry

[Ham-er]

Good Work.

[exray]

Very clever idea!

[gusnaz]

Great idea. I don't believe we have any walwarts with 220 volts in the states. Any one seen any?

Gus
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Old age is 'when you still have
something on the ball, but you are just too tired to bounce it.'

[XtalHWJ]

I find them occasionally at HSC Electronics. Very cheap... only a dollar or two. Sometimes under 50 cents. Not too useful as USA power supplies so they sell cheap.

Rich
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Homebrew Radio ex-Silicon Valley

[Georg]

BTW,
why and when did "someone" in USA decide to
stay with 110/120 Volt?
Has there been a serious dicussion about that?
Regards
Georg

[corne]

Journeyman,

Good idea and it looks great.

When I started with crystal sets I've tried several 230V wall-wart transformers, not as nice looking as yours, but with limited success. All wall-wart transformers I tried worked but they had relatively low primary inductance, only a few Henry's which resulted in attenuation of low frequencies, and significant losses.

Corné

[foolsgolden]

i cant resist trying that myself its the best idea for a boa-gen i ever seen, i got access to one of those. i am gonna try that today my x-tal set just so happens not to have a out put x former


Daniel
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A proud 28 yr. old member who shares and gets ideas...

[XtalHWJ]

[journeyman]

[corne]

journeyman,

I tried troid transformers as well. They generally have more inductance than the wall-wart transformers and less losses and work quite well. I didn't stop there and searched for even better transformers.
Current I'm using microphone transformers that where used in tube amplifiers to match the low microphone impedance (600ohm) to the high tube impedance (100kohm). These are ideal to match low impedance DLR5 headphones, which are about 200ohm with two elements in parallel, to the high impedance detector. Often the primary inductance of these transformers is higher than 100H. As with other types of transformers the losses vary from manufacture to manufacture. Some microphone transformers are tiny and still work quit well. Here's a picture of my mini crystal set using one of the tiny microphone transformers, look for the gray round thing to the right of the tuning capacitor.
Corné

[XtalHWJ]

Corne'

Is that gray object an "in-line" microphone transformer?

I have been using the Bogen T-725, as learned from Dave Schmarder.

Rich
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Homebrew Radio ex-Silicon Valley