Running Benchmark AHB2 in bridged mode and 4 Ohm Speaker

ramtubes319 posts12-07-2018 4:24am
"The 29 amps will only be supplied by the amplifier if the load resistance is low and the voltage is high enough to produce that current. Perhaps its the order of things. Voltage first, then resistance then figure the current. I think we have all come to agree that bridging does not allow the amplifier to provide more than 29 amps. Bridging just allows twice the voltage which increases the OPPORTUNITY for more current to flow, but its still limited to 29 amps."

Agreed, good post.

Ramtubes, AHB2 has load/line regulated SMPS, but as you mentioned, there are losses everywhere.  Exact doubling of power for half of the load means perfect regulation - an ideal voltage source, that is only possible with very deep negative feedback.  Such feedback might create instabilities or TIM distortions, but  feedback in AHB2 is quite different - it is non recursive, meaning that signal is not fed back to the input of the same amplifier but to another "error amplifier" that corrects output later.  Such arrangement eliminates instabilities (allowing for wide bandwidth of the amp) and TIM distortions.  I also noticed a lot of low bass added , in comparison to my previous class D amp (that had 5Hz low bandwidth limit).  My guess is that all DC servos have instability problems for very low frequencies, but AHB2, having no recursive feedback at all can go down to 0.4Hz.  Should 0.4Hz vs 5Hz difference be audible with 30Hz speakers? - I don't know, but it is in my setup (big surprise).  The same goes for the upper limit - more extension and airy treble.  Could this be phase delay at high frequencies with my class D amp?  Speaker itself has inductive character at higher frequencies accelerating phase.  In addition there are many amps, including one  of Lamm, that have lower (50kHz) bandwidth and are praised for wonderful airy highs.

I had mentioned in my review that the AHB2 is not able to drive the Kingsound King III electrostatic to an unlimited level of listening. However, there is no degradation of sound as the amp is pushed to its limit, and there is no degradation associated with mono use.

I had mentioned in my review that the AHB2 is not able to drive the Kingsound King III electrostatic to an unlimited level of listening. However, there is no degradation of sound as the amp is pushed to its limit, and there is no degradation associated with mono use.

How did one stereo amp sound to a level it was comfortable at, and then the bridged at the same level? To gauge which sounded better. Not which could go louder!

Cheers George

@kijanki 

Ramtubes, AHB2 has load/line regulated SMPS, but as you mentioned, there are losses everywhere. Exact doubling of power for half of the load means perfect regulation - an ideal voltage source, that is only possible with very deep negative feedback

Lets just take this first part. Feedback is not involved in doubling of power, deep or not. The losses I am speaking of are mostly in emitter resistors and turn on resistances of the output devices. Once an amp clips feedback cannot make up for these losses.