Originally Posted by DarKen23
I see. Man I really wish I knew the output input impedance of the A18 to determine weather or not a lightspeed attenuation control can be added.
Seeing that it has a 50k pot, that solves the question. The input impedance is 50k ohms, which barely qualifies for a passive pre. In order for a passive pre to outshine an active pre in most systems, the input impedance must be 47k or higher. You my friend do indeed have that option. You can go two routes with the ALPS pot. 1) Turn it all the way up which will effectively disable the pot, but the signal will still pass through it. 2) Remove it completely,tap the RCA jacks and add 50k+ resistors (i did 68k with my BH Crack) to L/R signal lines and jumper PCB path with wire where the pot was.
Side note, the lower the input impedance, the lower the potential for noise. However this makes it much harder for your source to drive it (bad for passive system). The higher the input impedance, the higher the potential for noise, but it makes it much easier for your source to drive (good for passive system). You will typically see input impedances anywhere from 47k to 100k. There are of course several amps with much lower input impedances, but those are not the norm.
Edited by brunk - 10/25/13 at 1:40pm