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In Reply to: Values of resistor on the secondaries of output transformer posted by akltam on December 30, 2012 at 05:59:03:
Since I didn't design the preamplifier, I can only guess at the purpose of the resistor. I suspect that it's a loading resistor for the tube. If the value of the resistor is fairly low, then it's probably used to flatten the output frequency response at high frequencies. You can't readily calculate the value of this resistor, but have to size it by looking at the frequency response and reducing the value until you suppress the high frequency circuit resonances without affecting the 20KHz response significantly. Personally I find that if this technique is applied too aggressively, the sound quality suffers a lot. If you need to, a better way to suppress the frequency "bump" caused by the primary tube/transformer capacitance circuit resonance is to use a "Zobel network" across the output transformer secondary. But first, remove the resistor and see how ithe preamp sounds.
Kevin Carter
K&K Audio
www.kandkaudio.com
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Follow Ups
- RE: Values of resistor on the secondaries of output transformer - KevinC 07:10:41 12/30/12 (0)