I have watched, in kind of amazement, at how this thread has gone back and forth.  My interest is that my offered answer of me being able to only use 2 of my 3 cabinets keeps getting thrown back and forth and it seems that the parties... Dave and Line 6, keep approaching the issues from different sides and never achieve a "meeting of the minds".  I'm certainly no god, but lets see if we can get to the bottom of the issue here....

As I have only read the LD manual (in regards to the LD-400) but own an LD-150 and a HD-400, I think I have a fairly good understanding of how they work.

The first issue is determining the power output of the LD-400, which when presented with a total 4 ohm load, should be 400 watts of output power.

Second if the internal speakers in the amp, rated to a 4 ohm load, there would be no ability to hang an external cabinet off the LD-400 as the total load would be represented by the speakers in the LD-400 unit.

If I have to take a guess, the speakers in the LD-400, if wired in parallel are 16 ohm speakers presenting an 8 ohm load to the LD-400.

Being that, hopefully I am still on a roll here, the LD-400 is only capable oif delivering around 275 watts (give or take) with only the interal speakers.

Now if you connect an 8 ohm, external load (extra cabinet) you will now load-down the amp to its maximum effeciency delivering a maximum of 400 watts to the internal speakers AND the external cabinet.  Meaning an external cabinet (of 8 ohms) MUST be connected for the amp to deliver FULL POWER !!

HOWEVER, if Line 6 is using a "switching" jack for the external (extension) cabinet and a resister pack, of 8 OHM value, then the amp *could* deliver the 400 watts to the internal speakers and when an external cabinet is connected, the resister pack would be taken out of the curcuit, allowing the external cabinet to perform the roll of the resister pack with additional speakers, thereby allowing the FULL 400 WATTS to be delivered with OR without the extension cabinet.  Leaving the only remining question that I cannot verify, because I DO NOT have an LD-400... Line 6... are you doing something along this line, or does my previous description apply... and that is something for Line 6 to answer...

Rich, based on your answer, rather than following the label on the product and the instructions in the manual, you have successfully told me why I wasted money buying new cabinets to accomodate the 4 ohm load instructions when I could have put that money to better use and continued using my three (3) original 8 ohm cabinets with the HD-400 like I had with my prior amp head.

At some point you put together definitive instructions that people either follow or they don't.  You cannot protect everyone from themselves, but you sure can disappoint responsible people who can read and follow instructions.

If this is the "complete" and "correct" answer, much appreciated, for future use purposes, only wish it had been the ONLY answer given !!!!

Regards,

Keith

An LD-150/HD-400 user

As opposed to being an abuser !!