O.T transformer question...

[Johan]

hello all...

just a little stupid question....I am puting together a fender champ clone and waiting for the output transformer...but I just cant wait...so reading the tubeampbook, it says the impedance ratio is the square of the voltage ratio..does that mean that a 220v to 22 volt transformer could make a 4k-to-4ohm transformer?...I realize it would probably be poor quality, but just while I'm waiting...
...yeah I know..airgap in single ended amps, core-saturation and such...
....and if so, if the same transformer has the primary devided into 0-110-220volt, could it pass for a sheap 8k A-A /8ohm...

Johan

[R.G.]

Your head is in the right place, but the math is a bit off.

220:22Vac is a 10:1 ratio, so the impedance ratio is 100:1. An 8 ohm load on the low voltage side is transformed to an 800 ohm load on the high voltage side. To do a 1000:1 transformation, you need a 31.6 voltage ratio, or 220:7Vac transformer. A 220:6.3V transformer might work OK. Something like a flat pack 120/120:6.3/6.3 transformer could be OK except for the gotchas that you already list.

Those gotchas include low primary inductance, which translates to poor low frequency response; high flux density, which will translate to high distortion from the transformer (primarily 3rd harmonic), intolerance of DC offset, etc. that you have already thought of.

The leakage inductance is not all that bad for the semi-toroidal flat pack transformers, but the results are not going to be all that good in the classical audio sense. You might like the quirks, though.

[Nasse]

There was a tube headphone amp project in Elektor magazine months or about year ago that used small pcb transformer as output amp. If I remeber right it was dual 18 V/230 V

perhaps something there (the author of the construction article)

http://www.b-kainka.de/

quess you can find something at elektor website, but it was less powerful amp than Champ

[Johan]

thanks guys...
might as well wait untill the proper one gets here in a few days then..

Johan