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RE: New schematics

Posted by KurtP (A) on March 4, 2015 at 06:32:17

In Reply to: New schematics posted by KevinC on September 11, 2014 at 07:28:51:

Hello Kevin:

Curious about the 2-stage PP amplifier schematic and the headphone amp. I have a 3-stage PP amplifier with interstages that I am going to be modding. I have a desire to eliminate the input phase splitter xfmr, as it doesn't have ideal performance. Going fully differential with a CCS to a negative supply is likely my choice for the first stage, similar to your headphone amp.

Removing the first-second stage IT is another possible goal if I can gain a performance increase. This leaves only one IT for the driver to the 3rd stage 300B's. Your headphone amp is a good option to do this. How stable are the DC operating points over the course of a month? Is this a set-it-and-forget-it design, or do you find that periodic tweaking is necessary? I really like the idea of DC coupling the stages to avoid having a capacitor.

On the other side of the thought process, simply forcing the first stage to be fully differential (as opposed to the Lynn Olson design) could allow the input transformer to remain, with its benefits of shielding and galvanic isolation. As long as I don't require phase balance performance from the input xfmr, it performs well. In other words, it does well transforming differential signals with low distortion, but it fails to provide accurate gain and phase relationship between the two secondaries.

Your thoughts ? Currently using LL1692A/PP (2:1.75) for IT, and LL1620AM/PP for OPT. Input transformers are selectable between a Tribute and Cinemag. Thanks!!

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