K&K Audio / Lundahl Transformers

Step up transformer required

58.174.202.66

Dear Sir/Maam,

I am writing from Australia. I have a set of new Japanese headphones from Taket, they are the model # H2 which are an unusual load to drive.

The headphones come with a step up transformer, model #TR2 but measurements have shown that it is too small and causes bass roll off. This transformer has a ratio of around 1:20, so for 10V in, you get 200V out. The transformer has an input impedance of 16 ohms. There is a 4.7 ohm resistor at the inputs to the transformer(s).

It was recommended to me to try one of your transformers, model #LL1620.

These are the headphones I have:

http://www.taket.jp/about2/about2.html

The translation is poor but I have done some tests and with help from some professionals I have these specifications.

Here is some advice I had from Vinnie Rossi at Red Wine Audio, whos single ended, 30watt x 2 solid state amplifier ( http://www.redwineaudio.com/Signature_30.2.html ) I am hoping to use your transformer with to drive the H2:

That amplifier puts out approx. 15.5 Vrms, is it possible for me to buy a transformer from you with a ratio of 1:40, so the 15V in will give 600V out? Or 1:30, so the 15V in will give 450V out?

"My guess based on your data is that a 1:40 ratio should be good (this is a "step-up" transformer). So if you give 10Vrms in, you get 400Vrms out.

Also, you don't want the input impedance of the transformer (the primary side) to go any lower than 4-ohm. If it does, a resistor in series will do the trick to raise it up and this is what Takei's design has. If it goes lower than 4-ohm, this is going to be too much of a load for the amp. I think 6 or 8 ohm input impedance would be even better.

As far as the output impedance, it needs to be fairly low. It sounds like the headphones have an approx 3k load, 60nF (at 10kHz).

I'm pretty sure that you will want the output impedance to be less than 300 ohms if possible (the lower, the better), and able to handle the 60nF and the 3k load of the headphones without any bass roll off or any high freq. roll-off. So you want 20Hz to 20kHz freq. response without rolloff if possible."

The H2 headphones can accept an absolute maximum peak of 1000 volts. The highest RMS voltage I have measured at the headphones during very loud music is 350 volts, the lowest volume I would listen to measured 0.1 volts on average.

The H2 headphones are a 60000 picofarad load.
at 10khz they are less than a 3k ohm load.

Is that enough information to figure out which transformer would give an excellent result from 20 - 20k Hz?

What specifications would an amplifier need in order to comfortably drive the H2 headphones through your transformer?

If you can provide a suitable transformer, please give me the details on the cost and how I can pay.

If you need more information, please ask me and I will find out.

Thanks and regards,

Steve

Follow Ups:

RE: Step up transformer required - KevinC 08:57:02 10/10/07 (0)

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