I'm looking for a not-too-expensive amp to drive a pair of KEF c55 speakers (4 ohms, 150W). My parents recently gave these to me, and they're in excellent condition.
I was thinking of the HK 3485. Is this 4 ohms stable? I was a bit confused because, although the specs list output at 4 ohms (150W per channel, 20 Hz - 20 kHz @ <0.2% THD), the speaker outputs on the back of the amp all read 8 ohms. The manual doesn't explicitly mention speaker impedence.
I was also considering the Denon DRA-297. I know this is 4 ohms stable, but it looks like it puts out a bit less power than the HK 3485.
Don't be concerned with on paper power specs or claims of stability into low impedance loads. Many manufacturers will not claim their amplifiers are stable at 4 Ohms since that measurement of a loudspeaker's load is not sufficient to fully suggest whether the amplifier will have a difficult time with the load. You need to know the lowest impedance point of the speaker, not the nominal or average or claimed impedance, along with the most severe electrical phase angle measurement. Just stating a nomimal impedance for a speaker tells you very little but does suggest the speaker is likely to fall beneath that specified number, so a nominal 4 Ohm speaker will probably fall beneath 4 Ohms at some point in its range. What happens to the phase angle at that point is what is most important. You can only find phase angle measurements in test reports or by calling the manufacturer.
Of course, speaker manufacturers are like amplifier manufacturers and some are more truthful than others about what their products can and will do. HK and KEF are respectable companies and they are likely to make a decent pairing. The HK amp is fairly sturdy and the KEF's are probably reasonably stable at somewhere around a 4 Ohm load with, in all likelyhood, a low phase angle. That's a guess on my part based on experience with the lines and not the two products you mention. You should contact the two companies for their specific advice on this pairing. There aren't absolutes to be given since music is dynamic in nature and variable in terms of power requirements. In other words, the proof is in the listening and you can try the HK if you aren't going to blast the volume and you provide sufficient air space around the amplifier. If the amp runs excessively warm at high volumes, you will have to consider other alternatives. Beyond that, unless someone here has specific experience with this combination, you should contact the companies for their recommendations.
Thanks for your advice. I just heard back from HK, and according to them the HK 3485 can support two 4 ohm speakers. I have taken your advice and contacted KEF to see if they have any suggestions on this pairing, but it looks like I should be ok. I'm in an apartment and keep my music fairly quiet in any case.