The sp200's amplifier section has only 2 channels, but it is designed in a "balanced" way. According to the THX guidelines, all XLR socket traces are returned to the amplifier. And because it is an unbalanced amplifying part, the RCA does not need to pass an XLR->RCA amplifier like the XLR input. Therefore, the performance of the RCA input is the best. We test the input using 5Vrms (because this is the best point of our ap's signal generator), the A-WTD is not used, the attachment is the result of the RCA and XLR inputs we tested, all with a 33OHM load, where the XLR input is 0.00009%, because this is the result of the 1st prototype test. For 2nd generation prototype, we modified the resistance of XLR-> RCA, THD+N down to 0.000085%, and the results of the five prototypes were consistent. BTW, we are using APX555B, I also attached THD+N of the APX555B 5Vrms.
A retrouver ici https://www.audiosciencereview.com/foru ... 42/page-10 (avec des copies d'écran auxquelles je ne comprend rien
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