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RE: Q About Edcor Transformer Performance

Thanks Matt, that's very helpful. My current phones are Grado, so I'm working with 32 ohms. However, I want the option of using other phones, so the ability to drive up to 600 ohms or so would be nice. My general idea for this is to output the signal at an impedance about midway between, then use resistive padding to match the amplifier. Headphones don't need much power (at least the Grados don't), so I'm thinking that one watt output or so should be plenty, even if some of the power is thrown away.

I don't want to reveal the tube I'm planning to use until I've built and tested this. It's one of those odd-looking things from the '40s, and the output stage will be somewhat unconventional. Output matching will be straightforward though, with the tube wanting a load of about 5K to produce a little less than 1W.

The Edcor GXSE 15K:600 looks promising for this. I was hoping its upper end might be somewhat extended if it was used at 5K:200, and the low end might see improvement at power levels below its rated 5W. Also, Edcor has said in e-mail that the primary winding will handle 80mA, well in excess of the 25 mA of my tube. Nevertheless, the frequency response rating of the transformer doesn't appear to be very meaningful, being measured at "< 1dBu."

The other approach I've considered is to use a CCS, a high quality coupling cap at the 5K primary, and Edcor's XSM 10K:150 or 10K:600 (operating Z would be 5K:75 or 5K:300). This approach would require much more testing though, due to the need for a solid-state CCS. I greatly dislike attaching semiconductors to the signal path. Even if the XSM meets its rating of 20Hz-20kHz in this application, it will require hours of subjective listening tests over a long period of time to convince me (and the other subjects I'll have to bring in) that we're not hearing the sand.

The alternative is to bite the bullet and spend $300-400 on OPTs made specifically for this use. I'm not sure I can justify that cost just for this purpose, so I want to understand all the less-expensive options first.

Thanks again for the helpful information!


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