ECP Audio DSHA-3F technical measurements If you are unfamiliar with audio measurements please use a search engine with the query: "audio measurements" or "audio measurement handbook" Look for publications by Richard C. Cabot and also by Bob Metzler, both from Audio Precision. There are other useful publications as well. These will provide basic knowledge. Interpretation of the following measurements is beyond the scope of this post. The data presented were collected as follows: 1. PrismSound dScope III, picoscope 5243B, Micsig DP10013 balanced probe, Keysight 34465A DMM 2. 300 and 30 ohm loads used for measurements 3. Balanced cables Canare L-4E6S starquad with Neutrik XLR connectors 4. Vaunix Lab Brick USB hub for measurement equipment 5. Audioquest Forest and Schiit Pyst USB cables used for measurement equipment 6. Amplifier gain adjusted to 0 dB gain @ 0.775 Vrms 0 dBu 7. DSHA-3F gain knob at approximately 2:30 to achieve 0 dB gain (varies a little between 30R and 300R load) 8. 14 and 16 AWG sheilded power cables used Reference data for two headphones to keep in mind: HD 650 impedance 300R, sensitivity 98 dB/mW HE-500 impedance 38R, sensitivity 89 dB/mW SPL levels for above headphones for reference: +9 dBu 300R 16.00 mW - 110 dBSPL @ 98dB/mW 0 dBu 300R 2.00 mW - 101 dBSPL @ 98dB/mW -10 dBu 300R 0.20 mW - 91 dBSPL @ 98dB/mW -20 dBu 300R 0.02 mW - 81 dBSPL @ 98dB/mW +9 dBu 30R 160.00 mW - 110 dBSPL @ 89dB/mW 0 dBu 30R 20.00 mW - 102 dBSPL @ 89dB/mW -10 dBu 30R 2.00 mW - 92 dBSPL @ 89dB/mW -20 dBu 30R 0.20 mW - 82 dBSPL @ 89dB/mW All testing performed at 0 dBu unless otherwise noted. This level is consistent with listening to headphones (referenced above) at 90 dBSPL average with peaks to 100 dBSPL, if the music has 10 dB Peak to Avg ratio. That is LOUD for long listening sessions. Highlights First, well done Doug! This is an incredible headphone amplifier. Nearly perfect gain linearity spanning over 110 dB range!!!!! +/- 1 dB gain linearity over 140 dB range!!!!! SNR greater than 116 dB!!!!! Tube magic midrange yet no tubes. Great square wave response, with a tight ring on rising and falling edges. Bandwidth: DC to greater than 115 KHz Bottom line DSHA-3F has been added to the A list of headphone amplifiers in the acoustic lab inventory. Test Data Organization Post 1 - introduction 1 - Bal input to 4XF output 300R load part 1 of 3 2 - Bal input to 4XF output 300R load part 2 of 3 3 - Bal input to 4XF output 300R load part 3 of 3 4 - Bal input to 4XF output 30R load part 1 of 3 5 - Bal input to 4XF output 30R load part 2 of 3 6 - Bal input to 4XF output 30R load part 3 of 3 7 - dynamic series 30R load My personal preferences include listening typically at an average of 75 dB SPL. Assuming a typical Peak to Average ratio of 10 dB puts peaks at 85 dB SPL. This suggests the measurements at -20 dBu represent my experience with HD6x0 and HD800 headphones. Auditory experiences for someone listening 10 dB SPL average higher may diverge from my own experiences. editorial - I believe there is a tendency to focus excessively on numbers such as THD attempting to reduce a complex topic to a single number representing a sort of goodness rating. Graphs can present far more data conveying a better understanding of the measurement over a range of frequency, levels, etc. Please don't read too much into the numbers presented. Read the tutorial presented here for a good example of why. Picture of Audio Lab setup for DSHA-3F measurements Output impedance measured 4.88R Bal input 4XF output 300 ohm load part 1 of 3 DSHA-3F THD+N THD nth harmonic distortion (A04) FFT 0dBu 300R load DSHA-3F Gain vs Amplitude 300R load Wow! Incredible gain linearity over such a large dynamic range for an amplifier!!! DSHA-3F THD THD+N vs Freq 0dBu 300R load DSHA-3F 1 KHz spectrum Left and Right 0dBu 300R load DSHA-3F 50 Hz + 7000 Hz spectrum Left and Right 0dBu 300R load 50 Hz stimulus resulting in low level harmonic series similar to tube amps! DSHA-3F 600 Hz + 1700 Hz spectrum Left and Right 0dBu 300R load DSHA-3F IMD spectrum Left and Right -16dBu 300R load Very clean IMD. DSHA-3F residual noise spectrum Left and Right A=0dB 300R load Residual noise is quite low.