I played around with my Velleman Digital Oscilloscope to measure the noise and maximum output voltage of the headphone output of Fiio E12DIY as well as other sources I have on my desk. The Fiio E12DIY Op-Amp and Buffer combination during the test were AD8620 and LME49600.
Maximum output voltage of the headphone output in VAC RMS:
Fiio E12DIY Low Gain: 2.23
Fiio E12DIY High Gain: 7.11
Yulong DA8: 6.75
Violectric HPA V200: 11.74 (measured with Amprobe AM-160 multimeter, as this level is higher than the maximum limit of the digital oscilloscope)
Mytek 192-DSD: 10.00 (measured with Amprobe AM-160 multimeter, as this level is higher than the maximum limit of the digital oscilloscope)
As for noise, what shown on the oscilloscope sometime not really correspond with what I heard through IEM. In this test I use JVC HA-FXD80 for IEM
(which died during the test due to an accident. I forgot that the Mytek was playing 100 Hz tone at full volume when I plugged my favorite IEM on the headphone output... stupid me... very sad now I have to use my second pair of JVC HA-FXD80)
All at maximum volume level, from what I heard using IEM, sorted from the lowest noise to the highest noise when playing silent track:
Fiio E12DIY @ Low Gain
Violectric HPA V200
Mytek 192-DSD using Digital volume control
Fiio E12DIY @ High Gain
Mytek 192-DSD using Analog volume control
The first four in the list, noise level are pretty close. Fiio E12DIY at lowest gain produce the lowest noise I could hear. Yulong DA8 headphone output, and Violectric HPA V200 connected to Yulong DA8 through balance connection, produce soft noise at maximum volume level. Considering Violectric HPA V200 output has the highest output voltage, this is amazing how Violectric HPA V200 can achieve such low noise level at that high amplification (0 dB gain adjustment).
Mytek 192-DSD headphone output with the analog volume control is the noisiest, like about 12 dB louder compared when using digital volume control. Using digital volume control, the noise is about the same as the Violectric HPA V200.
Somehow I don't know how to see the level of noise using the what shown on the oscilloscope. For example comparing the Mytek output noise, between analog volume control and digital volume control. They have about the same 1.5 mVAC rms (analog volume slightly higher), and while the digital volume control has higher DC offset, what I hear from the IEM, the analog volume was much noisier than the digital volume control.
Maybe someone knows how to interpret the oscilloscope measurement in relation to the noise level heard from the IEM?
Below are screen captures of the oscilloscope, while playing a silent track, and at maximum volume level.
The DC offset of Mytek 192-DSD headphone output is pretty high, but still safe for most IEMs and Headphones.
Fiio E12DIY @ Low Gain:
Fiio E12DIY @ High Gain:
Yulong DA8 Headphone Output:
Violectric HPA V200 headphone output, 0 dB gain adjustment, connected to Yulong DA8 through balance connection:
Mytek 192-DSD headphone output with analog volume control:
Mytek 192-DSD headphone output with digital volume control:
Edited by earfonia - 12/26/13 at 8:17am