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In Reply to: Not so hidden advertising posted by Thomas on January 25, 2001 at 10:14:47:
Thomas wrote:Oh I would not be so sure about that last sentence....
Well if you've any evidence that the circuit in the application note used two transformers instead of one to sell more transformers, I'm all ears.
And what's with the "Not so hidden advertising" topic? What not so hidden advertising are you referring to?
se
Follow Ups:
The more transformers he sells, the more money he makes. Thus, lots of iron in his designs. And why not?
Well, actually, I really don't have any evidence that points to that. But I am curious why Jensen didn't wind the transformer for balanced secondary operation as an option. A center tap would have been welcomed by lots of DIY'ers with a bent for balancing the whole shebang from input to output.
-Erik.
e.lektronick wrote:Well, actually, I really don't have any evidence that points to that. But I am curious why Jensen didn't wind the transformer for balanced secondary operation as an option. A center tap would have been welcomed by lots of DIY'ers with a bent for balancing the whole shebang from input to output.
Ok, I looked at the application note a bit more closely and realized why the circuit was done with two transformers instead of one. It wasn't for "effective" center tapped output, it was for the VOLTAGE GAIN.
The 115K-E is a 1:10 step up transformer. The circuit in the application note results in a 1:20 step up. So you get a voltage gain of 20 while retaining the performance of the 115K-E. All else being equal, when you increase the voltage gain of the transformer, you limit its low frequency performance with respect to maximum input level.
For example, compare the 115K-E to the 13K7-A, which is a 1:5 step up. The maximum 20 Hz input level for the 115K-E (the point at which THD reaches 1%) is -2.5dBu. The maximum 20 Hz input level for the 13K7-A is +7dBu. So the point of the circuit in the application note is to end up with a 1:20 step up transformer with the performance of their 1:10 step up.
se
OK, I get it. So, If I'm not worried about the voltage gain so much, I can make it up in the gain stage and use a single transformer. Cool.
Thanks. I'm starting to grasp it all, now.
Know any good sources of info that deal exclusively with input transformers? Besides the Jensen site, of course.
-Erik.
e.lektronick wrote:OK, I get it. So, If I'm not worried about the voltage gain so much, I can make it up in the gain stage and use a single transformer. Cool.
Yes. Though I'd still talk to Jensen about using the output of that particular transformer to drive both halves of a differential input.
Thanks. I'm starting to grasp it all, now.
Know any good sources of info that deal exclusively with input transformers? Besides the Jensen site, of course.Can't think of any general source offhand. But you might want to check out the web sites for both Lundahl and Sowter .
Good luck!
se
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