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THD+N Results I jumped around a lot in this video and did not always compare apples to apples. The notes below may help bring some clarification... I also later discovered that my dummy load had slightly inductive resistors causing skewed results in certain frequency ranges. I will eventually post a retest of these parameters with a different dummy load and analyzer. Base Line: 150W 2KHz [L Channel .077% ] / [R Channel .072%] 150W 3KHz & Up Over .1 % / Over .1% (THD+N Increased steadily above .1% as frequency increased) Frequency Response -3dB / -3dB @ 20KHz 1W (Siglent Oscillator) After Cleaning Controls & Chassis Ground Connection: (R Channel Rebuilt Driver Card) 2KHz 1W .049% / .038% 20KHz 1W .063% / .054% 2KHz 150W .071% / .072% 20KHz 150W .091% / .081% Frequency Response -1.2dB / -1.2dB @ 20KHz 1W (Siglent Oscillator) Frequency Response -.4dB / -.2dB @ 20KHz 1W (Tektronix Oscillator) After Both Driver Cards Updated: 2KHz 1W .034% / .039% 20KHz 1W .053% / .048% 2KHz 150W R & L Same (Not Captured on Video) 20KHz 150W R & L Same (Not Captured on Video) After input stage signal transistors and all output transistors replaced with modern substitutes: 2KHz 1W .026% / .024% 20KHz 1W .068% / .067% 150W Level not tested due to issues discovered with SG505 Oscillator Note: The residual THD+N of my test rig is .0025% I apologize for lack of consistency in test variables. The next time I do a test like this I will keep a spreadsheet with all results and keep all oscillator settings equal. In Part 4 of the Accuphase P-300 series, I track down a control issue causing improper frequency response and THD measurements, update the driver cards to service bulletin spec, and repair the right channel once again after I blow it up during testing. 00:00 - Introduction 01:23 - Base Line Tests 06:25 - Filter Control Chassis Ground 08:06 - Post Cleaning Retest 12:04 - Driver Card Modifications 15:22 - Post Modification Testing 16:26 - Blown Up Channel Repair 21:22 - Tektronix Oscillator Oscillation 24:04 - Final Build Tests