> Is this measured with high impedance probes? If I remember correctly, > small > caps limit low-frequency response of K3 especially with low impedance > phones/speakers. > Ignacy
Correct, measured with a 2K-ohm load resistance at the sound card input. The purpose of the test was to measure only the response plots as a result of changes in DSP versions. To get a ruler-flat response down to 20 Hz with headphones may require a change in C9/C13 on the Main DSP Board, depending on the Z of your headphones at that frequency. I changed C9/C13 with 330uF units and this work well with any commercial headphones. If you refer to the K3's schematic, note that 8-ohm series build-out resistors are used and appear "off-page." The addition of the build-out resistors has the effect of improving low-end response as the headphone Z decreases. As a practical matter, and assuming one is using newer headphones with a Z of at least 30 ohms at roughly 50 Hz, then Elecraft's revised Main DSP Board with 100uF caps at C9/C13 are completely sufficient. More info here: http://www.n1eu.com/K3/k3audiomod.htm W9AC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
