Reviewed on: SoundStage! Solo, March 2020
I measured the IL-DSP using a Clio 10 FW audio analyzer, a Neutrik NL-1 Minilyzer, and TrueRTA software with an M-Audio MobilePre USB interface. Because my Clio 10 FW analyzer isn’t compatible with USB-only devices, I could only run very basic measurements; I had to plot most of them by hand, or use noise signals with a spectrum analyzer. Note that my focus with these tests is on measurements that confirm these devices’ basic functionality.
This chart shows the matching of the IL-DSP channels at 1mW into a 32-ohm load at a 44.1kHz sampling rate. This measurement does show some roll-off before it hits 20kHz, but when I tried the same measurement using white noise and a spectrum analyzer, I didn’t see this roll-off. Mainly what to take away from this is that that response is basically flat and the channels are well-matched; the left channel is -0.048dB below the right channel at 1kHz, an inaudible difference.
This chart shows the output of the IL-DSP vs. total harmonic distortion (THD) into 32- and 250-ohm loads at 1kHz. Rated power is 30mW into 32 ohms at 0.0007% THD. Output into 32 ohms is 37mW at 0.5% THD and 39mW at 1% THD. Output into 250 ohms is 4.7mW at 0.5% THD and 5.1mW at 1% THD. That means that with something like the Sennheiser HD 600 headphones (rated 300 ohms, 97dB sensitivity), you’ll get about 103dB max usable volume, which is not enough for full dynamics.
Output impedance at 1kHz is rated at 1.08 ohms (according to the support community forum on miniDSP’s website); I measured 0.31 ohm. Either way, the amp’s output impedance will not interact significantly with the reactance of headphones or earphones, and thus won’t alter their frequency response -- although of course the reason you would buy this product is to change the headphones’ frequency response.
. . . Brent Butterworth