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Power Output of Class "D" amps



I have noticed a lot of discussion about class D amps in the past weeks. One thing bothers me. The most of the amps are rated high outputs into 8 ohms. Upon looking at the power into 4 ohms, the power is less that the normal doubling of output we see in most class A/B, and class A amps. I have been told ( maybe incorrectly ), that class D amps do drop in power output as the impedance falls. I am not sure since I am not an engineer. What does seem to be a common thread is that, especially the Spectron’s, seem to sound better when run in the mono block config. I wonder if the power supply sections of the class D amp are not as stout as traditional amps, again one popular company offers several thousand dollars of factory mods ?? to a finished product, to improve the sound. In what section of the amp do most of these mods take place, the power supply. I for one hate to buy a product that needs to be made better the day I buy it. Could the quality of the power supply sections of class D amps not be meeting the demands of the designs ?? or are they just cutting cost ??

Class D amps are a confusing lot. Some call them digital, others do not. Yet, they do switch on and off, at fantastic rates. Some companies even tout the fact that they switch so fast that they are super, super fast, so they sound better. That is also a funny fact, since may people here have stated that increased sample rates in CD players, ( switching ), decreases sound quality.

Last time I checked, sound when created I real life, is a group of waves that are unbroken, until the sound ends, or is made to stop on purpose. I believe we call that analog sound. If the sound that is fed to our speakers is a product of the input being switched on and off, not matter how fast, then it is not analog, but what ??, even if the designers are claiming that it recombined, isn’t it always wanting to play catch up ??

Could the decrease in power output into decreasing ohm values, be a lack of true analog tracking ??, and could this be the reason why class D amps sound better when run as mono blocks. Maybe it’s because it’s only then that they have the capability handle complex loads, and meet the expectations of the owners. Is 600 watts of Class D actually only equal to 300 watts of class A/B or Class A

I’d really appreciate if some qualified technical people would reply, along with all the regulars.

Fire away.
brimmer5000

Showing 1 response by nick778

nick778
147 posts
 
I have a Spectron MK2 with V-Cap and have hear them in my system mono-block and using one in stereo.

First off, there is plenty of power for 95% of the speakers made with just one amp. My B&W 803D mains are nominally rated at 8 ohm but can dip to between 2-3 ohms. The one amp has no problems driving the speakers into low or high volumes. To the contrary, this is one reason I like the amp. You don't loose anything at low volumes with the massive power reserves. My speakers recommend up to 500 watts of power an do indeed like power. Many 802D owners like the mono-block set-up as the power demands are higher with those speakers in reality.

The situation is just about the same with tradtion A/B amps like the Classe CAM 400 mono-blocks. They are going to sound better than the CA-2200 due to the higher power reserves and that they are balanced; the Spectron is balanced also in the mono mode.

The amp is also stable down to 0.1 ohms which may explain why the wattage doesn't quite double from 8 ohms to 4 ohm to 2 ohms. Not too many amps, class D or not, will produce specs for their amps at 2 ohms (1200 watts for the Spectron) since they are not continously stable there and/or the distortion increases too much to do so, imo.

High end electrostatic speakers like Apogees can dip below 1 ohm regularly and the Spectron does excel here and a mono-block set-up may be better depending on the manuafacturer's recommended power specs.

Spectron designs their own IECs rather than buying B&O's IEC so it can build it to any spec it wants rather than tweak the B&O IEC modules.

I also like the Bel Cantos especially the new REF1000 II that is an updated and modified version of the original REF1000.
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