What Class D amps will drive a 2 ohm load

@georgehifi  super efficient easy to drive horns

Hi George, been following these class D threads, what's wrong with efficient easy to drive horns? I'm a neophyte in these matters and trying to learn.

Thank you 

Bel Canto 600M monoblocks. Powerful, 2 ohm stable, incredible detail, etc, etc.

what’s wrong with efficient easy to drive horns?

If you need to ask that, you should delve into the measurements of both a bit  

To have that efficiency and easy load ability. Measurement tests show they are always compromised when compared to a highly tuned speaker eg Wilsons ect ect, that will be far more inefficient and much harder load, that yes need far more serious drive characteristics from the amp/s
Bit like comparing a high octane highly tuned multi cam/valve Ferrari V8 motor, to a low octane V8 Ford iron slug from the 60’s.

Cheers George

This statement is false. The ability to double power as load impedance is halved has nothing to do with how well the amp will play bass

Of course it does when it demands current into low impedance to do it, get over it.!

George, the quote above suggests that you do not understand how a voltage source works.


In case you don't understand what a voltage source is, solid state amps that can double power as impedance is halved are behaving as a voltage source. Having a low enough output impedance is for the most part what makes for a voltage source. A voltage source is defined as a circuit that can make the same voltage (not power) output into whatever load it drives. Now no circuit can really do this perfectly; perfection does not exist. So constant voltage is considered load invariant under the Voltage Paradigm rules. Historically ElectroVolice and MacIntosh led the way to this concept back in the late 1950s.


To be a voltage source, the circuit does not have to double power as impedance is halved. But it very much has to be able to cut power in half as impedance is doubled! This is why tube amplifiers can operate as voltage sources and its also why a solid state amp that can't double power into even 4 ohms can nevertheless still play bass correctly into a 2 ohm load. Whatever power it makes into 2 ohms, to act correctly without distortion it will be half of that into 4 and half again into 8 ohms.


So for those amps that do not have the power supply capacity, or the current capacity to survive higher powers in the output section, or for tube amplifiers which are well-known to not double power as impedance is halved, the designer simply has to make sure that the amplifier has enough negative feedback so as to reduce the output impedance such that the circuit behaves as a voltage source into the expected loads.


If the amplifier innately has a low enough output impedance it may not need the feedback to achieve constant voltage operation. An example of this are the Ayre amplifiers. But any class D amp (GaNFET or not, even sans feedback) has a low enough output impedance as well. So as long as they are operated in their linear region 2 ohms is no problem.


Again, this is defined by output impedance. In the case of a class D amp, the output impedance formula is dominated by the 'on' resistance of the output devices. Even in an older MOSFET based class D amp, the output impedance is usually well below 0.1 ohm, meaning that they will have at least 20:1 damping factor into a 2 ohm load. If the amp runs feedback (and most of them do) the output impedance will be even lower than that.


The real issue of a class D amplifier driving 2 ohms is actually the filter at the output. What I regard as a bit odd here is that while you have acknowledged numerous times in other discussion the issues of a filter at the output of the amp, in this particular discussion you've not brought out this salient fact even once! This leads me to think that you have no idea what you're talking about. (Please note that what I think you know and what you actually know are likely two different things.) BTW, the way to deal with the filter issue is to design the filter to operate at as high a frequency as possible- hence the advantage of GaNFETs as they allow a much higher filter frequency since the switching frequency is so much higher. This allows the filter to still be effective for hifi purposes when presented with a 2 ohm load.


You like to routinely discount my comments out of hand and insult me at every turn, despite the fact that I went to school for this sort of thing and actually design amps (including GaNFET class D amps) for a living. You're a fan on Nelson Pass- why not ask him?

My two cents:

1) George is an extremely rude individual. Would you honestly speak to people in person the way you do here? Why go out of your way to insult an engineer who designs and builds excellent products and is wiling to impart information? Are you willing to share your audio CV so we have an understanding of your expertise, as your comments do not suggest you do not have much of an understanding of even basic electrical concepts (i.e. ohm’s law)?

2) Atmasphere is extremely patient. Thank you you for continued information. Your posts are always informative for those looking for more technical information without getting deep into the math.