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      04-02-2012, 08:59 PM   #60
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Originally Posted by Technic View Post
The jury is still out on the HD amps... two years ago I installed a HD900/5 in a HiFi M3 and it was great. Very straight forward install, sounded great without any processor.

Fast forward two years and a coded EPS-HiFi M3 with two HD600/4 (the one in the picture) and no processing showed some changes in sound quality and compatibility that I'm still trying to understand. For example, although the power output should be the same all the way down to 1.5ohms, a 2 ohms load sounds considerably louder than a 4ohms load. Setting their input level to high sounds slightly better than setting it at low, as it should be (it is HiFi as it was with the HD900/5). Installing a MS-8 in between the CIC and the HD amps have shown similar results, so it is not a matter of balanced inputs.

No XD amp have shown issues like that with HiFi outputs.

Something must have changed in these amps that when the customer contacted JL Audio to ask about these issues their "fix" was to install a Cleansweep.
Originally Posted by Technic View Post
According to the customer, yes. I did not install the MS-8, I only calibrated it once after the install and still it sounded to me that the rears were getting a slightly higher power than the fronts.
Originally Posted by Technic View Post
I tried both and still I could hear higher volume in the back. To be clear, this is not higher as in "damn this is louder!" than the fronts, just enough to notice. And because I already noticed this without the MS-8 then it became obvious that something is not quite right in here.
Originally Posted by goodoleme View Post

The one HD-600/4 I came over with was NIB from JL. I did switch the amps (HD-600/4s) and I got the same uneven power output with the 2ohms vs 4ohms!
I did some thinking on this after Ken had pointed me to a post on DVC sub wiring: Even though the RIPS is maintaining constant wattage to the 2ohm channels, you still have 2x the voice coil which means you still have +3dB, assuming constant wattage.

Above 4ohms, the 600/4 will halve the available power...i.e. 75wpc. But since you still have 2x voice coil you get that 3dB back, so you are back to (rears+sides)=fronts. Thus I think you should wire in series (according to the manual this is a supported load).

Edit: I can't account for the different behavior of the PDX under this theory.