Amplifier Distortion vs Amplitude Technical Measurements In this first installment three low cost schiit headphone amplifiers are compared. Test conditions: Selectable gain set to high Amplifier gain adjusted for 0 dB input to output Load 300 Ω Ultron 7DJ8 tube in Vali 2+ Magni Heresy top Magni 3+ bottom More measurements: Heresy https://www.superbestaudiofriends.org/index.php?threads/magni-heresy-technical-measurements.8613/ Magni 3+ https://www.superbestaudiofriends.org/index.php?threads/magni-3-technical-measurements.8612/ Magni Vali 2+ with Ultron 7DJ8 tube More Vali 2+ measurements: https://www.superbestaudiofriends.org/index.php?threads/vali2-technical-measurements.10250/ Amplifier Negative Feedback Negative FeedBack (NFB) involves subtracting a fraction of the open loop Amplifier gain stage output from its input. That fraction is shown as β in the diagram above. β = NFB dB and the terms will be used interchangeably. NFB dB values reported in the following graphs are approximate as they are a simplification from gain-bandwidth plots. These distortion sweeps were performed over the range of +20 to -20 dBu. FFT trace is distortion spectrum at 0 dBu. Bandwidth for distortion observations is 22 Hz to 22 KHz unless otherwise noted. Trace ID: Yellow: THD+N Green: D2 Tan: D3 Red: 4+HD+N with bandwidth 400 Hz to 22 KHz Blue: FFT distortion spectrum at 0 dBu 4+HD+N is also called Crap Factor™ and the terms are used interchangeably. A tutorial on these graphs available here: https://www.superbestaudiofriends.o...distortion-vs-amplitude-a-visual-guide.12279/ Vali 2+ distortion vs amplitude Many headphones have sensitivity such that 0 dBu will produce approximately 100 to 105 dB SPL. While interesting to observe amplifier behavior above 0 dBu the range of significant interest is below 0 dBu. Note the yellow box in the graph above surrounding Red Crap Factor™ trace -20 to 0 dBu. Also note NFB dB = 8 for the Vali 2+. Magni 3+ distortion vs amplitude While the THD+N is very different from that of the Vali 2+ observe the CF is nearly identical. Yet the Magni 3+ uses 30 dB of NFB. Magni Heresy distortion vs amplitude THD+N and CF are nearly the same as Magni 3+, yet Heresy has 115 dB of NFB. Animation of the previous three measurements Again, observe how CF is nearly the same for all three but considerably different amounts of NFB are utilized for each amplifier design. Several key points to remember: 1. THD+N masks differentiating distortion components 2. Each amp has different D2 / D3 sweep signatures 3. THD+N @ 1 KHz is 0.00216% for Heresy and 0.00252% for Magni – very similar – yet sweeps demonstrate clear differences between them 4. 4+HD+N is nearly identical for all three amps in the range of interest SBAF preference poll of these three headphone amps may be found here: https://www.superbestaudiofriends.o...ce-poll-of-three-schiit-headphone-amps.12312/ Between these measurements and the SBAF poll one might infer a preference exists for amplifiers with lower NFB needed to achieve a particular CF distortion performance. 20220529 Poll Results to date: 20220530 edited to correct THD+N typos in key point values.