Originally Posted by lukeamdman
The 14k is only 14k if it's 2ohm stable, which the clone is not.
And, the 7500 can't be bridged.
It depends on the application.
I assume that all discussions in this thread refer to power for a subwoofer. There are 2 things to consider; 1) frequency response down low and 2) bridged vs 2 channel operation.
A while back, I posted about the discrepancy in roll off of some of the clone-type amps I measured. I'm not aware of anyone posting the roll off of the Peavey or other amps, but in my case (sealed L/T systems), the roll off is as important as anything else. I bought 2 amps from a different supplier and hooked them up to test them under fire from the usual ULF heavy hitters. I noticed a difference in the presentation (and saw it on the SpecLab waterfall graphs) and decided to measure the FR of some older amps vs the newer ones.
The new amps begin to roll off at 20 Hz and are -3dB @ 7 Hz, while the older amps were -3dB @ 3.5 Hz. There's approx 5dB difference @ 3 Hz between the old and new amps I tested. My theory is that the factory that builds them just uses the blocking caps they use for the 4 channel version and/or the blocking caps values aren't of any concern to them because "as you know, amplifiers don't work well below 20 Hz anyway".
The other issue I discovered while messing with amplifiers is a phenomenon called Bus Pumping. This happens particularly a low frequencies, so it was something I wanted to look into. For anyone interested, searching the term will lead to descriptions, but the short of it is that a simple cure for the problem is to bridge the amplifiers. I suspect this is why Speakerpower and the rest of the recent lightweight switching supply amps are not bridgeable, because they are a full bridge configuration out of the gate. IOW, each channel is already bridged, therefore the 2 channels cannot be bridged.
Basically, bus pumping occurs when voltage fluctuations result in reverse power coming back to the supply from the amp. The lower the frequency and the lower the load, the worse it is. And, we use extremely low impedance loads at extremely low frequencies at maximum power levels and current. The simple cure is to bridge the 2 channels so that the excess power is consumed by the out of phase channel. It eliminates bus pumping.
I suspect that this is why the clones failed under sine wave duress in 2 channel mode at 2 ohms at the lowest frequency used for the tests. It's my opinion that most of the failures cited in this thread are the result of driving subs in 2 channel mode. I could be mistaken but it might be something to look into as far as a failure and what mode of operation correlation. I also suspect that this is why I never have had a problem because I only ever use the amps in bridged mode. I also feed the amps into a 4 ohm nominal load with a signal chain that has virtually zero roll off to 2 Hz and, again, have never had a problem.
So, IMO, so-called tests of the LG or any similar versions that use sine waves at low frequencies into a low impedance load PER CHANNEL, are all bogus for my application, YMMV. I would not recommend using any switching power supply amplifier for subwoofer duty unless it's a full bridge configuration amp or unless it's bridgeable and you use it only in bridged mode. 2 channel mode above 100 Hz is not a problem at any load, IMO.
Rated power output is the most suspect number for comparisons and roll off and configuration are much more important is HT subs (ULF) are the end game. If the Peavey or whatever amp is down -15dB @ 3 Hz, then what is its actual output capability vs an amp that's down -4db @ 3 Hz when playing WOTW? Etc.