Test setup
Distortion Test at 1kHz into 8 ohms
N.B. 6 V ac is this test setup maximum limit. Tests: 43 Hz to 96 kHz FFT
1 kHz sine (see TPA graph for comparison of harmonic structures). THD+N at 2 watts into 8 ohms = 0.0058%
19 kHz + 20 kHz Intermodulation.
Residual noise for above tests (signal = mute). TPA6120 Line Driver Comparison Tests
1 kHz sine (see amplifier graph for comparison of harmonic structures). TPA6120 THD+N = 0.005%
19 kHz + 20 kHz Intermodulation.
TPA6120 Residual noise for above tests (signal = mute). Notes:These tests were performed "open" on the bench. It is interesting to compare the harmonic structure of the TPA6120 Line Driver loop-back only tests with that of the amplifier. In these and the other tests on this page and elsewhere is is apparent that the signal source has an appreciable effect on the test results, for example with the relative levels of the second and third harmonics. A valve based source should therefore maintain the valve quality of the sound, and a solid state source should also retain it's own signature. The FFTs results are all produced on scales which are +10 to -180 dB. The signal floor is discernable below 140 dB and whilst "noisy" still shows effects and structure. For example in the three amplifier test graphs the wavy undulation is a function of the FFT sampling aliasing with 50 Hz pickup in the transformers.
80 Hz to 96 kHz FFT
First FFT results.
1 kHz sine wave, 800 Hz to 96 kHz, 4.11 Vac, 2 Watts into 8 ohms.
A series of tests to confirm basic operation of the test setup and put the above results into context.
E-mu 1212M residual input noise with XLR cable - open circuit.
Amplifier ON, Input Open Circuit, 8 ohm load.I guess the stuff up above 30 kHz is the switching power supplies in the computer and monitor. Apart for the interference pickup the residual noise is about the same as the soundcard.
Amplifier OFF, Input Open Circuit, 8 ohm load.As previous test but with the amplifier power off for comparison. That pickup above 30 kHz still there.
TPA6120 Line driver output.This is the output from the TPA6120 headphone amp chip (with OP275 and SSM2015), source HP 8903B 1 kHz sine wave (peak is at -6 dB on the graph = 4.11 Vac), direct to the 1212M input.
Amplifier ON, input from TPA6120 nominally zero signal, 8 ohm load..This is the output from the TPA6120 headphone amp chip, source HP 8903B 1 kHz sine wave, with attenuator set to minimum. Theoretically no signal to the amplifier. FFT Analysis by WINaudioMLS softwarePRO EX Version + 64-bit ultra high precision FFT; 192kHz/24 Bit ASIO support. This page last modified on: 23rd October 2005 All information, drawings and images Copyright © 1995 - 2006 Susan Parker unless otherwise credited. |