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Amp Designs That Are Able To Drive 4/2 Ohms Load

I have noticed that some amps like the Krell Evo 302 will output the exact wattage when halving the impedances ie. 300W/600W/1200W into 8/4/2 ohms respectively. On the other hand, some amps like the Bryston 7B-SST does not output the exact wattage when halving the impedances ie. 600W/8 ohms to 900W/4 ohms or the Plinius SA-100 (100W/8 ohms to 180W/4 ohms)

Can someone enlighten as to where the 'missing' watts have gone for amps that do not output the exact 2X the wattage when going from an 8 ohm to 4 ohm load? What are the criterias in amp design that determine which route to adopt, and what are the pros and cons of each design?

Thanks in advance.
ryder
electroid
283 posts
 
When an amp can't double its power as the impedance halves, the power supply is to blame. I have a CJ MF-2500A and it doubles down to two ohms.

ET
starcon
98 posts
 
the critical factor is the power supply. There is a reason a big amp has a huge power supply. also number of output transistors and size of capacitors can be big factors. Great amps also tend to weigh more than lesser amps. (of course there are class d amp-IMO are a complete waste of space)
muralman1
1,527 posts
 
Starcon, and what class A or class AB are you touting to be superior to class D amps in general, and the large power supply loaded H2O in particular? With the help of it's stable mate, the Fire, this duo can power my 1 ohm speakers with ease, delivering huge dynamic swings along with loads of musical detail.
Post removed 
eldartford
4,262 posts
 
As Bob noted, inability to drive a 2 ohm load does not reflect "Crappy" design. It reflects inteligent design (sorry about that) for an amp that will be used with 8 or 4 ohm speakers.

If you want to drive low impedance loads look to pro sound amps that are designed to do this.
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