I've always heard that it is alright to use a "Y" adaptor from a preamp out, or split the signal from an actual preamp for biamping, adding a sub, or whatever. I have not done this a lot but my experience is this can have an adverse effect. Here's what happens.

I have an Adcom gtp-450 and gfa-5500. This is my Rock-n-Roll system in my work out room. I have an old Infinity sub I wanted to add to enhance the bottom octave. I put a "Y" adaptor on the preamp's output with one leg of each channel to the sub and the other to the amp. When I do this the lower octaves are about the same maybe a bit more but the mains lose punch and midbass. No, there isn't any crossover involved here. The only one is the adjustable low pass on the sub. Here's my theory maybe some one who is tech minded can say if it's valid.

#1. the "Y" adaptor addition cut the voltage to my power amp and it isn't getting what it needs. It's bad, the system sounds much better without the sub.

#2 Which I plan to prove or disprove soon. I wouldn't think any phase issues would come into play from the cables but I plan to switch channels to see what happens. I don't think placement phase is an issue since I suspected this problem with my 5400 but it's really obvious with the 5500. The sub didn't sound that bad with the 5400.

#3 Maybe the sub has a lower input impedance and it gets most of the juice?

OK, looks like #2 is the main problem with preliminary switch of the cables. At the sub I traded inputs with the cables, this made an immediate and noticeable improvement. I wonder if this is what that phase switch on the back of some subs do. I'll do more listening late which should show if problem is cured.

Anyone ever have this happen or care to take a stab at what is going on?